Adaptor protein ClpS is an essential regulator of prokaryotic ATP-dependent protease ClpAP, which delivers certain protein substrates with specific amino acid sequences to ClpAP for degradation. However, ClpS also functions as the inhibitor of the ClpAP-mediated protein degradation for other proteins. Here, we constructed the clpS-overexpression Mycobacterium smegmatis strain, and showed for the first time that overexpression of ClpS increased the resistance of M. smegmatis to rifampicin that is one of most widely used antibiotic drugs in treatment of tuberculosis. Using quantitative proteomic technology, we systematically analyzed effects of ClpS overexpression on changes in M. smegmatis proteome, and proposed that the increased rifampicin resistance was caused by ClpS-regulated drug sedimentation and drug metabolism. Our results indicate that the changes in degradation related proteins enhanced drug resistance and quantitative proteomic analysis is an important tool for understanding molecular mechanisms responsible for bacteria drug resistance.
In our prior publications we characterized a conserved acetylation motif (K(R)xxKK) of evolutionarily related nuclear receptors. Recent reports showed that peroxisome proliferator activated receptor gamma (PPAR?) deacetylation by SIRT1 is involved in delaying cellular senescence and maintaining the brown remodeling of white adipose tissue. However, it still remains unknown whether lysyl residues 154 and 155 (K154/155) of the conserved acetylation motif (RIHKK) in Ppar?1 are acetylated. Herein, we demonstrate that Ppar?1 is acetylated and regulated by both endogenous TSA-sensitive and NAD-dependent deacetylases. Acetylation of lysine 154 was identified by mass spectrometry (MS) while deacetylation of lysine 155 by SIRT1 was confirmed by in vitro deacetylation assay. An in vivo labeling assay revealed K154/K155 as bona fide acetylation sites. The conserved acetylation sites of Ppar?1 and the catalytic domain of SIRT1 are both required for the interaction between Ppar?1 and SIRT1. Sirt1 and Ppar?1 converge to govern lipid metabolism in vivo. Acetylation-defective mutants of Ppar?1 were associated with reduced lipid synthesis in ErbB2 overexpressing breast cancer cells. Together, these results suggest that the conserved lysyl residues K154/K155 of Ppar?1 are acetylated and play an important role in lipid synthesis in ErbB2-positive breast cancer cells.
The assembly and maintenance of cilia depends on intraflagellar transport (IFT). Activated IFT motor kinesin-II enters the cilium with loaded IFT particles comprising IFT-A and IFT-B complexes. At the ciliary tip, kinesin-II becomes inactivated, and IFT particles are released. Moreover, the rate of IFT entry is dynamically regulated during cilium assembly. However, the regulatory mechanism of IFT entry and loading/unloading of IFT particles remains elusive. We show that the kinesin-II motor subunit FLA8, a homolog of KIF3B, is phosphorylated on the conserved S663 by a calcium-dependent kinase in Chlamydomonas. This phosphorylation disrupts the interaction between kinesin-II and IFT-B, inactivates kinesin-II and inhibits IFT entry, and is also required for IFT-B unloading at the ciliary tip. Furthermore, our data suggest that the IFT entry rate is controlled by regulation of the cellular level of phosphorylated FLA8. Therefore, FLA8 phosphorylation acts as a molecular switch to control IFT entry and turnaround.
Drug resistance poses a major challenge to ovarian cancer treatment. Understanding mechanisms of drug resistance is important for finding new therapeutic targets. In the present work, a cisplatin-resistant ovarian cancer cell line A2780-DR was established with a resistance index of 6.64. The cellular accumulation of cisplatin was significantly reduced in A2780-DR cells as compared with A2780 cells consistent with the general character of drug resistance. Quantitative proteomic analysis identified 340 differentially expressed proteins between A2780 and A2780-DR cells, which involve in diverse cellular processes, including metabolic process, cellular component biogenesis, cellular processes, and stress responses. Expression levels of Ras-related proteins Rab 5C and Rab 11B in A2780-DR cells were lower than those in A2780 cells as confirmed by real-time quantitative PCR and Western blotting. The short hairpin (sh)RNA-mediated knockdown of Rab 5C in A2780 cells resulted in markedly increased resistance to cisplatin whereas overexpression of Rab 5C in A2780-DR cells increases sensitivity to cisplatin, demonstrating that Rab 5C-dependent endocytosis plays an important role in cisplatin resistance. Our results also showed that expressions of glycolytic enzymes pyruvate kinase, glucose-6-phosphate isomerase, fructose-bisphosphate aldolase, lactate dehydrogenase, and phosphoglycerate kinase 1 were down-regulated in drug resistant cells, indicating drug resistance in ovarian cancer is directly associated with a decrease in glycolysis. Furthermore, it was found that glutathione reductase were up-regulated in A2780-DR, whereas vimentin, HSP90, and Annexin A1 and A2 were down-regulated. Taken together, our results suggest that drug resistance in ovarian cancer cell line A2780 is caused by multifactorial traits, including the down-regulation of Rab 5C-dependent endocytosis of cisplatin, glycolytic enzymes, and vimentin, and up-regulation of antioxidant proteins, suggesting Rab 5C is a potential target for treatment of drug-resistant ovarian cancer. This constitutes a further step toward a comprehensive understanding of drug resistance in ovarian cancer.
Glutathione (GSH) is the most abundant tripeptide in human cells and plays an important role in protecting cells' integrity against oxidative stress. GSH has an unusual amide linkage formed between the ?-carboxylic group of the glutamic acid in its side-chain and the amine group of cysteine residue. In the present study, we have compared reactivities of GSH to its isomer GluCysGly (ECG), which has a regular amide bond formed between the ?-carboxylic group of glutamic acid and the amine group of cysteine residue. The fragmentation pattern of GSH ions in the gas phase is different from that of ECG ions, showing that the loss of H2O is the major dissociation pathway in ECG fragmentation. This is consistent with the dissociation pathway predicted by density functional calculation. Formation of GSSG from oxidation of GSH is faster than that of ECG disulfide, and the gas phase fragmentation pattern of GSSG is different from that of ECG disulfide. GSH and ECG display similar rates in nucleophilic aromatic substitution when reacting with 1-chloro-2,4-dinitrobenzene (CDNB). However, in the presence of glutathione S-transferases (GST), substitution of CDNB by GSH is 10 times faster than that by ECG. GSH and ECG also show differences in clustering patterns in the gas phase. Taken together, our results shed light on understanding effects of unique boding structure in GSH on its stability and reactivities.
The aim of this study was to find serum biomarkers of rheumatoid arthritis (RA) by high-resolution proteomic analysis. Low-abundance proteins from pooling serum sample of early RA patients and healthy controls were enriched using ProteoMiner™ enrichment kits. The enriched proteins were separated on SDS-PAGE, digested by trypsin, labeled with tandem mass tag (TMT) reagents, and desalted by C18 stage tip column. Then, the labeled peptides were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) with nano-LC combined with Orbitrap Q Exactive mass spectrometer, and experiments were carried out three times using different specimens, and differentially expressed proteins were screened by intensity ratios of identified peptides. Enzyme-linked immunosorbent assays (ELISAs) were performed to confirm differentially expressed proteins. Twenty-six proteins were found differentially expressed in RA serum by high-resolution proteomic analysis. Among them, levels of thrombospondin-1, ficolin-2, isoform 10 of fibronectin, and apolipoprotein E were higher in RA patients than in healthy controls (RA/healthy control (HC) ? 1.5, p<0.05), while levels of angiotensinogen, paraoxonase/arylesterase 1, isoform E of proteoglycan 4, and plasminogen were significantly lower (RA/HC ? 0.67, p<0.05). Further study by ELISA showed a higher level of ficolin-2 in the serum of RA patients compared to healthy controls; the level of ficolin-2 was found to be positively correlated with swollen joint counts (SJCs), disease activity score (DAS28), rheumatoid factor, and IgM in RA patients and with DAS28 and IgM in early RA patients through statistical analysis. The results of this study suggest that ficolin-2, as a newly screened biomarker by high-resolution quantitative proteomic analysis, offers the potentiality to become a diagnostic or disease evaluation tool in RA.
Neddylation, the covalent attachment of ubiquitin-like protein Nedd8, of the Cullin-RING E3 ligase family regulates their ubiquitylation activity. However, regulation of HECT ligases by neddylation has not been reported to date. Here we show that the C2-WW-HECT ligase Smurf1 is activated by neddylation. Smurf1 physically interacts with Nedd8 and Ubc12, forms a Nedd8-thioester intermediate, and then catalyses its own neddylation on multiple lysine residues. Intriguingly, this autoneddylation needs an active site at C426 in the HECT N-lobe. Neddylation of Smurf1 potently enhances ubiquitin E2 recruitment and augments the ubiquitin ligase activity of Smurf1. The regulatory role of neddylation is conserved in human Smurf1 and yeast Rsp5. Furthermore, in human colorectal cancers, the elevated expression of Smurf1, Nedd8, NAE1 and Ubc12 correlates with cancer progression and poor prognosis. These findings provide evidence that neddylation is important in HECT ubiquitin ligase activation and shed new light on the tumour-promoting role of Smurf1.
Rab GTPases, by targeting to specific membrane compartments, play essential roles in membrane trafficking. Lipid droplets (LDs) are dynamic subcellular organelles whose growth is closely linked to obesity and hepatic steatosis. Fsp27 is shown to be required for LD fusion and growth by enriching at LD-LD contact sites. Here, we identify Rab8a as a direct interactor and regulator of Fsp27 in mediating LD fusion in adipocytes. Knockdown of Rab8a in the livers of ob/ob mice results in the accumulation of smaller LDs and lower hepatic lipid levels. Surprisingly, it is the GDP-bound form of Rab8a that exhibits fusion-promoting activity. We further discover AS160 as the GTPase activating protein (GAP) for Rab8a, which forms a ternary complex with Fsp27 and Rab8a to positively regulate LD fusion. MSS4 antagonizes Fsp27-mediated LD fusion activity through Rab8a. Our results have thus revealed a mechanistic signaling circuit controlling LD fusion and fatty liver formation.
The in vivo assembly of ribosomal subunits is a highly complex process, with a tight coordination between protein assembly and rRNA maturation events, such as folding and processing of rRNA precursors, as well as modifications of selected bases. In the cell, a large number of factors are required to ensure the efficiency and fidelity of subunit production. Here we characterize the immature 30S subunits accumulated in a factor-null Escherichia coli strain (?rsgA?rbfA). The immature 30S subunits isolated with varying salt concentrations in the buffer system show interesting differences on both protein composition and structure. Specifically, intermediates derived under the two contrasting salt conditions (high and low) likely reflect two distinctive assembly stages, the relatively early and late stages of the 3' domain assembly, respectively. Detailed structural analysis demonstrates a mechanistic coupling between the maturation of the 5' end of the 17S rRNA and the assembly of the 30S head domain, and attributes a unique role of S5 in coordinating these two events. Furthermore, our structural results likely reveal the location of the unprocessed terminal sequences of the 17S rRNA, and suggest that the maturation events of the 17S rRNA could be employed as quality control mechanisms on subunit production and protein translation.
The identification of specific substrates of glutathione S-transferases (GSTs) is important for understanding drug metabolism. A method termed bioorthogonal identification of GST substrates (BIGS) was developed, in which a reduced glutathione (GSH) analogue was developed for recognition by a rationally engineered GST to label the substrates of the corresponding native GST. A K44G-W40A-R41A mutant (GST-KWR) of the mu-class glutathione S-transferases GSTM1 was shown to be active with a clickable GSH analogue (GSH-R1) as the cosubstrate. The GSH-R1 conjugation products can react with an azido-based biotin probe for ready enrichment and MS identification. Proof-of-principle studies were carried to detect the products of GSH-R1 conjugation to 1-chloro-2,4-dinitrobenzene (CDNB) and dopamine quinone. The BIGS technology was then used to identify GSTM1 substrates in the Chinese herbal medicine Ganmaocongji.
Preeclampsia (PE) is considered to be a potentially fatal complication during pregnancy. However, no effective laboratory assessment has been developed to enable early diagnosis and monitoring of PE. The present study aimed to identify differentially expressed transthyretin (TTR) during severe PE and evaluate TTR as a possible biomarker of this disease. TTR levels were determined in the different gestational weeks of normal pregnancy (before 20 weeks, n=41; after 20 weeks, n=39) using enzyme-linked immunosorbent assay (ELISA). TTR concentrations in pregnant females with severe PE (n=43) were compared with those in healthy matched control subjects (n=37) using western blot analysis and ELISA. The median TTR concentration during severe PE in each month of gestation was significantly lower than the concentrations recorded during normal pregnancy. TTR levels in females with severe PE were significantly downregulated compared with the control subjects (P<0.001; area under the curve, 0.834-0.967). Thus, TTR may be used as a potential biomarker of PE.
Nicotinamide adenine dinucleotide (NAD) is a coenzyme found in all living cells and mediates multiple cellular signaling pathways. In the present study, a 35% decrease of cellular NAD level is achieved by stable expression of the N-terminal truncated CD38, a NAD hydrolase. CD38-expressing (CD38(+)) cells have the lower growth rate and are more susceptive to oxidative stress than the wild type cells and empty vector-transfected (CD38(-)) cells. Quantitative proteomic analysis shows that 178 proteins are down-regulated in CD38(+) cells, which involve in diverse cellular processes including glycolysis, RNA processing and protein synthesis, antioxidant, and DNA repair. Down regulation of six selected proteins is confirmed by Western blotting. However, down-regulation of mRNA expressions of genes associated with glycolysis, antioxidant, and DNA repair is less significant than the corresponding change in protein expression, suggesting the low NAD level impairs the protein translational machinery in CD38(+) cells. Down-regulation of antioxidant protein and DNA-repair protein expression contributes to the susceptibility of CD38(+) cells to oxidative stress. Taken together, these results demonstrate that CD38(+) cells are a useful model to study effects of the cellular NAD levels on cellular processes and establish a new linker between cellular NAD levels and oxidative stress.
Protein arginine N-methyltransferase 3 (PRMT3) belongs to the family of type I PRMTs and harbors the activity to use S-adenosyl-l-methionine (SAM) as a methyl-donor cofactor for protein arginine labeling. However, PRMT3s functions remain elusive with the lacked knowledge of its target scope in cellular settings. Inspired by the emerging Bioorthogonal Profiling of Protein Methylation (BPPM) using engineered methyltransferases and SAM analogues for target identification, the current work documents the endeavor to systematically explore the SAM-binding pocket of PRMT3 and identify suitable PRMT3 variants for BPPM. The M233G single point mutation transforms PRMT3 into a promiscuous alkyltransferase using sp(2)-?-sulfonium-containing SAM analogues as cofactor surrogates. Here the conserved methionine was defined as a hot spot that can be engineered alone or in combination with nearby residues to render cofactor promiscuity of multiple type I PRMTs. With this promiscuous variant and the matched 4-propargyloxy-but-2-enyl (Pob)-SAM analogue as the BPPM reagents, more than 80 novel proteins were readily uncovered as potential targets of PRMT3 in the cellular context. Subsequent target validation and functional analysis correlated the PRMT3 methylation to several biological processes such as cytoskeleton dynamics, whose roles might be compensated by other PRMTs. These BPPM-revealed substrates are primarily localized but not restricted in cytoplasm, the preferred site of PRMT3. The broad localization pattern may implicate the diverse roles of PRMT3 in the cellular setting. The revelation of PRMT3 targets and the transformative character of BPPM for other PRMTs present unprecedented pathways toward elucidating physiological and pathological roles of diverse PRMTs.
Protein methyltransferase (PMT)-mediated posttranslational modification of histone and nonhistone substrates modulates stability, localization, and interacting partners of target proteins in diverse cellular contexts. These events play critical roles in normal biological processes and are frequently deregulated in human diseases. In the course of identifying substrates of individual PMTs, bioorthogonal profiling of protein methylation (BPPM) has demonstrated its merits. In this approach, specific PMTs are engineered to process S-adenosyl-L-methionine (SAM) analogs as cofactor surrogates and label their substrates with distinct chemical modifications for target elucidation. Despite the proof-of-concept advancement of BPPM, few efforts have been made to explore its generality. With two cancer-relevant PMTs, EuHMT1 (GLP1/KMT1D) and EuHMT2 (G9a/KMT1C), as models, we defined the key structural features of engineered PMTs and matched SAM analogs that can render the orthogonal enzyme-cofactor pairs for efficient catalysis. Here we have demonstrated that the presence of sulfonium-?-sp(2) carbon and flexible, medium-sized sulfonium-?-substituents are crucial for SAM analogs as BPPM reagents. The bulky cofactors can be accommodated by tailoring the conserved Y1211/Y1154 residues and nearby hydrophobic cavities of EuHMT1/2. Profiling proteome-wide substrates with BPPM allowed identification of >500 targets of EuHMT1/2 with representative targets validated using native EuHMT1/2 and SAM. This finding indicates that EuHMT1/2 may regulate many cellular events previously unrecognized to be modulated by methylation. The present work, therefore, paves the way to a broader application of the BPPM technology to profile methylomes of diverse PMTs and elucidate their downstream functions.
The DNA damage checkpoint is tightly controlled. After its activation, the checkpoint machinery is inactivated once lesions are repaired or undergoes adaptation if the DNA damage is unable to be repaired. Protein acetylation has been shown to play an important role in DNA damage checkpoint activation. However, the role of acetylation in checkpoint inactivation is unclear. Here we show that histone deacetylase Rpd3-mediated deacetylation of Rad53 plays an important role in checkpoint adaptation. Deletion of Rpd3 or inhibition of its activity impairs adaptation. RPD3 deletion also leads to a higher acetylation level and enhanced kinase activity of Rad53. Replacement of two major acetylation sites of Rad53 with arginine reduces its activity and further suppresses the adaptation defect of rpd3? cells, indicating that Rpd3 facilitates adaptation by preventing Rad53 overactivation. Similar to its role in adaptation, deletion of RPD3 or inhibition of its activity also suppressed checkpoint recovery. Altogether, our findings reveal an important role of Rpd3 in promoting checkpoint adaptation via deacetylation and inhibition of Rad53.
Breast cancer is a leading form of cancer in the world. The Drosophila Dac gene was cloned as an inhibitor of the hyperactive epidermal growth factor (EGFR), ellipse. Herein, endogenous DACH1 co-localized with p53 in a nuclear, extranucleolar compartment and bound to p53 in human breast cancer cell lines, p53 and DACH1 bound common genes in Chip-Seq. Full inhibition of breast cancer contact-independent growth by DACH1 required p53. The p53 breast cancer mutants R248Q and R273H, evaded DACH1 binding. DACH1 phosphorylation at serine residue (S439) inhibited p53 binding and phosphorylation at p53 amino-terminal sites (S15, S20) enhanced DACH1 binding. DACH1 binding to p53 was inhibited by NAD-dependent deacetylation via DACH1 K628. DACH1 repressed p21CIP1 and induced RAD51, an association found in basal breast cancer. DACH1 inhibits breast cancer cellular growth in an NAD and p53-dependent manner through direct protein-protein association.
Nucleotide-binding and oligomerization domain-like receptor (NLR) proteins oligomerize into multiprotein complexes termed inflammasomes when activated. Their autoinhibition mechanism remains poorly defined. Here, we report the crystal structure of mouse NLRC4 in a closed form. The adenosine diphosphate-mediated interaction between the central nucleotide-binding domain (NBD) and the winged-helix domain (WHD) was critical for stabilizing the closed conformation of NLRC4. The helical domain HD2 repressively contacted a conserved and functionally important ?-helix of the NBD. The C-terminal leucine-rich repeat (LRR) domain is positioned to sterically occlude one side of the NBD domain and consequently sequester NLRC4 in a monomeric state. Disruption of ADP-mediated NBD-WHD or NBD-HD2/NBD-LRR interactions resulted in constitutive activation of NLRC4. Together, our data reveal the NBD-organized cooperative autoinhibition mechanism of NLRC4 and provide insight into its activation.
Azacytidine is an inhibitor of DNA methyltransferase and is known to be an anti-leukemic agent to induce cancer cell apoptosis. In the present study, multiple myeloma cells were treated with azacytidine at clinically relevant concentrations to induce necrosis through oxidative stress. Necrotic myeloma cells exhibit unique characteristics, including enrichment of the cell-bound albumin and overexpression of endoplasmic reticulum (ER)- and mitochondrial-specific chaperones, which were not observed in other necrotic cells, including HUH-7, A2780, A549, and Hoc1a. Proteomic analysis shows that HSP60 is the most abundant up-regulated mitochondrial specific chaperone, and azacytidine-induced overexpression of HSP60 is confirmed by western blot analysis. In contrast, expression levels of cytosolic chaperones such as HSP90 and HSP71 were down-regulated in azacytidine-treated myeloma cells, concomitant with an increase of these chaperones in the cell culture medium, suggesting that mitochondrial chaperones and cytosolic chaperones behave differently in necrotic myeloma cells; ER- and mitochondrial-chaperones being retained, and cytosolic chaperones being released into the cell culture medium through the ruptured cell membrane. Our data suggest that HSP60 is potentially a new target for multiple myeloma chemotherapy.
Ribosome assembly is a process fundamental for all cellular activities. The efficiency and accuracy of the subunit assembly are tightly regulated and closely monitored. In the present work, we characterized, both compositionally and structurally, a set of in vivo 50S subunit precursors (45S), isolated from a mutant bacterial strain. Our qualitative mass spectrometry data indicate that L28, L16, L33, L36 and L35 are dramatically underrepresented in the 45S particles. This protein spectrum shows interesting similarity to many qualitatively analyzed 50S precursors from different genetic background, indicating the presence of global rate-limiting steps in the late-stage assembly of 50S subunit. Our structural data reveal two major intermediate states for the 45S particles. Consistently, both states severally lack those proteins, but they also differ in the stability of the functional centers of the 50S subunit, demonstrating that they are translationally inactive. Detailed analysis indicates that the orientation of H38 accounts for the global conformational differences in these intermediate structures, and suggests that the reorientation of H38 to its native position is rate-limiting during the late-stage assembly. Especially, H38 plays an essential role in stabilizing the central protuberance, through the interaction with the 5S rRNA, and the correctly orientated H38 is likely a prerequisite for further maturation of the 50S subunit.
Glutaredoxins (Grxs) have been identified across taxa as important mediators in various physiological functions. A chloroplastic monothiol glutaredoxin, AtGRXS16 from Arabidopsis thaliana, comprises two distinct functional domains, an N-terminal domain (NTD) with GlyIleTyr-TyrIleGly (GIY-YIG) endonuclease motif and a C-terminal Grx module, to coordinate redox regulation and DNA cleavage in chloroplasts. Structural determination of AtGRXS16-NTD showed that it possesses a GIY-YIG endonuclease fold, but the critical residues for the nuclease activity are different from typical GIY-YIG endonucleases. AtGRXS16-NTD was able to cleave ?DNA and chloroplast genomic DNA, and the nuclease activity was significantly reduced in AtGRXS16. Functional analysis indicated that AtGRXS16-NTD could inhibit the ability of AtGRXS16 to suppress the sensitivity of yeast grx5 cells to oxidative stress; however, the C-terminal Grx domain itself and AtGRXS16 with a Cys123Ser mutation were active in these cells and able to functionally complement a Grx5 deficiency in yeast. Furthermore, the two functional domains were shown to be negatively regulated through the formation of an intramolecular disulfide bond. These findings unravel a manner of regulation for Grxs and provide insights into the mechanistic link between redox regulation and DNA metabolism in chloroplasts.
In the present work, metabolomic and redox proteomic analyses were carried out on an untreated- and gossypol-treated ovarian cancer cell line, SKOV3. Gossypol treatment resulted in cell death through oxidative stress. Metabolite analysis showed that gossypol induces a decrease of the cellular levels of GSH, aspartic acid, and FAD. Using a combination of double labeling and LC-MS-MS, we identified changes in thiol-redox states of 545 cysteine-containing peptides from 356 proteins. The frequently occurring amino acid residue immediately before or after the cysteine in these peptides is the non-polar and neutral leucine, valine, or alanine. These redox sensitive proteins participate in a variety of cellular processes. We have characterized the redox-sensitive cysteine residues in PKM2, HSP60, malate dehydrogenase and other proteins that play important roles in metabolism homeostasis and stress responses. The three cysteine residues of HSP60 exhibit different responses to gossypol treatment: an increase of thiol/disulfide ratio for the Cys447 residue due to a decrease of the cellular GSH level, and a decrease of thiol/disulfide ratios for Cys442 and Cys237 residues due to oxidation and sulfation. This study suggests that thiol/disulfide ratios are dependent on the level of cellular GSH. Our data provide a valuable resource for deciphering the redox regulation of proteins and for understanding gossypol-induced apoptosis in ovarian cancer cells.
Standard methods for body fluid identification typically rely on detection of the functional proteins specific to or enriched in them, such as hemoglobin in blood, alkaline phosphatase and PSA in semen, or ?-amylase in saliva. While these markers can be relatively specific, the multiple methods used to identify them frequently rely on nonspecific chemical, enzymatic, or antibody reactions that usually require the structural integrity of the markers and are not confirmatory because other proteins or substances can also give positive test results. Recent advances in proteomics and mass spectrometry offer the ability to simultaneously detect multiple body fluid protein markers in a single, confirmatory test. Here, multiple markers for blood, saliva, and semen are identified by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). Data demonstrate the ability to detect these body fluids at nanoliter to subnanoliter levels and to distinguish mixtures. Protein stability of mock samples assayed after 16 months showed no diminution of signal. Because multiple peptides from multiple protein markers are detected and effectively sequenced by MALDI MS/MS, the assay is confirmatory. As mass spectrometry detects whatever peptides are present in a sample, no a priori knowledge of an unknown stain is necessary to perform the test.
In the present study, monocytes were treated with 5-azacytidine (azacytidine), gossypol or hydrogen peroxide to induce cell death through oxidative stress. A shift from apoptotic to necrotic cell death occurred when monocytes were treated with 100 µM azacytidine for more than 12 hours. Necrotic monocytes exhibited characteristics, including enrichment of cell-bound albumin and up-regulation of endoplasmic reticulum (ER)- and mitochondrial-specific chaperones to protect mitochondrial integrity, which were not observed in other necrotic cells, including HUH-7, A2780, A549 and HOC1a. Our results show that the cell-bound albumin originates in the culture medium rather than from monocyte-derived hepatocytes, and that HSP60 is a potential binding partner of the cell-bound albumin. Proteomic analysis shows that HSP60 and protein disulfide isomerase are the most abundant up-regulated mitochondrial and ER-chaperones, and that both HSP60 and calreticulin are ubiquitinated in necrotic monocytes. In contrast, expression levels of the cytosolic chaperones HSP90 and HSP71 were down-regulated in the azacytidine-treated monocytes, concomitant with an increase in the levels of these chaperones in the cell culture medium. Collectively, our results demonstrates that chaperones from different organelles behave differently in necrotic monocytes, ER- and mitochondrial chaperones being retained and cytosolic and nuclear chaperones being released into the cell culture medium through the ruptured cell membrane. HSP60 may serve as a new target for development of myeloid leukemia treatment.
In ciliated cells, two types of microtubules can be categorized: cytoplasmic and axonemal. It has been shown that axonemal tubulins come from a cytoplasmic pool during cilia regeneration. However, the identity and regulation of this pool is not understood. Previously, we have shown that Chlamydomonas kinesin-13 (CrKin13) is phosphorylated during flagellar regeneration, and required for proper flagellar assembly. In the present study, we show that CrKin13 regulates depolymerization of cytoplasmic microtubules to control flagellar regeneration. After flagellar loss and before flagellar regeneration, cytoplasmic microtubules were quickly depolymerized, which was evidenced by the appearance of sparse and shorter microtubule arrays and increased free tubulins in the cell body. Knockdown of CrKin13 expression by RNA interference inhibited depolymerization of cytoplasmic microtubules and impaired flagellar regeneration. In vitro assay showed that CrKin13 possessed microtubule depolymerization activity. CrKin13 underwent phosphorylation during microtubule depolymerization, and phosphorylation induced targeting of CrKin13 to microtubules. The phosphorylation of CrKin13 occurred at residues S100, T469 and S522 as determined by mass spectrometry. Abrogation of CrKin13 phosphorylation at S100 but not at other residues by inducing point mutation prevented CrKin13 targeting to microtubules. We propose that CrKin13 depolymerizes cytoplasmic microtubules to provide tubulin precursors for flagellar regeneration.
The Fc-III tag is a newly developed fusion tag that can be applied to protein purification and detection. In the present work, we use the Fc-III-tagged green fluorescent protein (GFP) and human muscle creatine kinase (CK) as model systems to investigate effects of the Fc-III tag on activities and stabilities of the expressed multicysteine-containing proteins. Our results show the Fc-III tag has no adverse effects on the fluorescence of GFP and reduces the occurrence of GFP misfolding due to incorrect Cys oxidation compared with the His-tagged protein. The activity and stability of the Fc-III-tagged CK is slightly lower than that of the tag-free CK, but is higher than that of the His-tagged CK as determined by the ratio of the oxidized versus reduced CK. A major portion of His-tagged CK is in its oxidized form, while that of the Fc-III-tagged CK is in its reduced form. A folding model of CK with different tags was proposed, which may provide insights into the effect of the Fc-III tag on the conformations of disulfide-bridged proteins.
Jasmonate regulates critical aspects of plant development and defense. The F-box protein CORONATINE INSENSITIVE1 (COI1) functions as a jasmonate receptor and forms Skp1/Cullin1/F-box protein COI1 (SCF(COI1)) complexes with Arabidopsis thaliana Cullin1 and Arabidopsis Skp1-like1 (ASK1) to recruit its substrate jasmonate ZIM-domain proteins for ubiquitination and degradation. Here, we reveal a mechanism regulating COI1 protein levels in Arabidopsis. Genetic and biochemical analysis and in vitro degradation assays demonstrated that the COI1 protein was initially stabilized by interacting with ASK1 and further secured by assembly into SCF(COI1) complexes, suggesting a function for SCF(COI1) in the stabilization of COI1 in Arabidopsis. Furthermore, we show that dissociated COI1 is degraded through the 26S proteasome pathway, and we identified the 297th Lys residue as an active ubiquitination site in COI1. Our data suggest that the COI1 protein is strictly regulated by a dynamic balance of SCF(COI1)-mediated stabilization and 26S proteasome-mediated degradation and thus maintained at a protein level essential for proper biological functions in Arabidopsis development and defense responses.
Bacteria, exemplified by enteropathogenic Escherichia coli (E. coli), rely on elaborate acid resistance systems to survive acidic environment (such as the stomach). Comprehensive understanding of bacterial acid resistance is important for prevention and clinical treatment. In this study, we report a previously uncharacterized type of acid resistance system in E. coli that relies on L-glutamine (Gln), one of the most abundant food-borne free amino acids. Upon uptake into E. coli, Gln is converted to L-glutamate (Glu) by the acid-activated glutaminase YbaS, with concomitant release of gaseous ammonia. The free ammonia neutralizes proton, resulting in elevated intracellular pH under acidic environment. We show that YbaS and the amino acid antiporter GadC, which exchanges extracellular Gln with intracellular Glu, together constitute an acid resistance system that is sufficient for E. coli survival under extremely acidic environment.
Protein methyltransferases (PMTs) have emerged as important epigenetic regulators in myriad biological processes in both normal physiology and disease conditions. However, elucidating PMT-regulated epigenetic processes has been hampered by ambiguous knowledge about in vivo activities of individual PMTs particularly because of their overlapping but nonredundant functions. To address limitations of conventional approaches in mapping chromatin modification of specific PMTs, we have engineered the chromatin-modifying apparatus and formulated a novel technology, termed clickable chromatin enrichment with parallel DNA sequencing (CliEn-seq), to probe genome-wide chromatin modification within living cells. The three-step approach of CliEn-seq involves in vivo synthesis of S-adenosyl-L-methionine (SAM) analogues from cell-permeable methionine analogues by engineered SAM synthetase (methionine adenosyltransferase or MAT), in situ chromatin modification by engineered PMTs, subsequent enrichment and sequencing of the uniquely modified chromatins. Given critical roles of the chromatin-modifying enzymes in epigenetics and structural similarity among many PMTs, we envision that the CliEn-seq technology is generally applicable in deciphering chromatin methylation events of individual PMTs in diverse biological settings.
In the present study, we have established a new methodology to analyze saliva proteins from HIV-1-seropositive patients before highly active antiretroviral therapy (HAART) and seronegative controls. A total of 593 and 601 proteins were identified in the pooled saliva samples from 5 HIV-1 subjects and 5 controls, respectively. Forty-one proteins were found to be differentially expressed. Bioinformatic analysis of differentially expressed salivary proteins showed an increase of antimicrobial proteins and decrease of protease inhibitors upon HIV-1 infection. To validate some of these differentially expressed proteins, a high-throughput quantitation method was established to determine concentrations of 10 salivary proteins in 40 individual saliva samples from 20 seropositive patients before HAART and 20 seronegative subjects. This method was based on limited protein separation within the zone of the stacking gel of the 1D SDS PAGE and using isotope-coded synthetic peptides as internal standards. The results demonstrated that a combination of protein profiling and targeted quantitation is an efficient method to identify and validate differentially expressed salivary proteins. Expression levels of members of the calcium-binding S100 protein family and deleted in malignant brain tumors 1 protein (DMBT1) were up-regulated while that of Mucin 5B was down-regulated in HIV-1 seropositive saliva samples, which may provide new perspectives for monitoring HIV-infection and understanding the mechanism of HIV-1 infectivity.
Ribosome biogenesis is a tightly regulated, multi-stepped process. The assembly of ribosomal subunits is a central step of the complex biogenesis process, involving nearly 30 protein factors in vivo in bacteria. Although the assembly process has been extensively studied in vitro for over 40 years, very limited information is known for the in vivo process and specific roles of assembly factors. Such an example is ribosome maturation factor M (RimM), a factor involved in the late-stage assembly of the 30S subunit. Here, we combined quantitative mass spectrometry and cryo-electron microscopy to characterize the in vivo 30S assembly intermediates isolated from mutant Escherichia coli strains with genes for assembly factors deleted. Our compositional and structural data show that the assembly of the 3-domain of the 30S subunit is severely delayed in these intermediates, featured with highly underrepresented 3-domain proteins and large conformational difference compared with the mature 30S subunit. Further analysis indicates that RimM functions not only to promote the assembly of a few 3-domain proteins but also to stabilize the rRNA tertiary structure. More importantly, this study reveals intriguing similarities and dissimilarities between the in vitro and the in vivo assembly pathways, suggesting that they are in general similar but with subtle differences.
MELK (maternal embryonic leucine zipper kinase), which is a member of the AMPK (AMP-activated protein kinase)-related kinase family, plays important roles in diverse cellular processes and has become a promising drug target for certain cancers. However, the regulatory mechanism of MELK remains elusive. Here, we report the crystal structure of a fragment of human MELK that contains the kinase domain and ubiquitin-associated (UBA) domain. The UBA domain tightly binds to the back of the kinase domain, which may contribute to the proper conformation and activity of the kinase domain. Interestingly, the activation segment in the kinase domain displays a unique conformation that contains an intramolecular disulfide bond. The structural and biochemical analyses unravel the molecular mechanisms for the autophosphorylation/activation of MELK and the dependence of its catalytic activity on reducing agents. Thus, our results may provide the basis for designing specific MELK inhibitors for cancer treatment.
Transforming growth factor ? (TGF-?) is a potent antiproliferative factor in multiple types of cells. Deregulation of TGF-? signaling is associated with the development of many cancers, including leukemia, though the molecular mechanisms are largely unclear. Here, we show that Casitas B-lineage lymphoma (c-Cbl), a known proto-oncogene encoding an ubiquitin E3 ligase, promotes TGF-? signaling by neddylating and stabilizing the type II receptor (T?RII). Knockout of c-Cbl decreases the T?RII protein level and desensitizes hematopoietic stem or progenitor cells to TGF-? stimulation, while c-Cbl overexpression stabilizes T?RII and sensitizes leukemia cells to TGF-?. c-Cbl conjugates neural precursor cell-expressed, developmentally downregulated 8 (NEDD8), a ubiquitin-like protein, to T?RII at Lys556 and Lys567. Neddylation of T?RII promotes its endocytosis to EEA1-positive early endosomes while preventing its endocytosis to caveolin-positive compartments, therefore inhibiting T?RII ubiquitination and degradation. We have also identified a neddylation-activity-defective c-Cbl mutation from leukemia patients, implying a link between aberrant T?RII neddylation and leukemia development.
Subclass III SnRK2s (SnRK2.6/2.3/2.2) are the key positive regulators of abscisic acid (ABA) signal transduction in Arabidopsis thaliana. The kinases, activated by ABA or osmotic stress, phosphorylate stress-related transcription factors and ion channels, which ultimately leads to the protection of plants from dehydration or high salinity. In the absence of stressors, SnRK2s are subject to negative regulation by group A protein phosphatase type 2Cs (PP2C), whereas the underlying molecular mechanism remains to be elucidated. Here we report the crystal structure of the kinase domain of SnRK2.6 at 2.6-? resolution. Structure-guided biochemical analyses identified two distinct interfaces between SnRK2.6 and ABI1, a member of group A PP2Cs. Structural modeling suggested that the two interfaces lock SnRK2.6 and ABI1 in an orientation such that the activation loop of SnRK2.6 is posited to the catalytic site of ABI1 for dephosphorylation. These studies revealed the molecular basis for PP2Cs-mediated inhibition of SnRK2s and provided important insights into the downstream signal transduction of ABA.
Major histocompatibility complex class II (MHC II) molecules are expressed on the surface of antigen-presenting cells and display short bound peptide fragments derived from self- and nonself antigens. These peptide-MHC complexes function to maintain immunological tolerance in the case of self-antigens and initiate the CD4(+) T cell response in the case of foreign proteins. Here we report the application of LC-MS/MS analysis to identify MHC II peptides derived from endogenous proteins expressed in freshly isolated murine splenic DCs. The cell number was enriched in vivo upon treatment with Flt3L-B16 melanoma cells. In a typical experiment, starting with about 5 × 10(8) splenic DCs, we were able to reliably identify a repertoire of over 100 MHC II peptides originating from about 55 proteins localized in membrane (23%), intracellular (26%), endolysosomal (12%), nuclear (14%), and extracellular (25%) compartments. Using synthetic isotopically labeled peptides corresponding to the sequences of representative bound MHC II peptides, we quantified by LC-MS relative peptide abundance. In a single experiment, peptides were detected in a wide concentration range spanning from 2.5 fmol/?L to 12 pmol/?L or from approximately 13 to 2 × 10(5) copies per DC. These peptides were found in similar amounts on B cells where we detected about 80 peptides originating from 55 proteins distributed homogenously within the same cellular compartments as in DCs. About 90 different binding motifs predicted by the epitope prediction algorithm were found within the sequences of the identified MHC II peptides. These results set a foundation for future studies to quantitatively investigate the MHC II repertoire on DCs generated under different immunization conditions.
Elucidating physiological and pathogenic functions of protein methyltransferases (PMTs) relies on knowing their substrate profiles. S-adenosyl-L-methionine (SAM) is the sole methyl-donor cofactor of PMTs. Recently, SAM analogues have emerged as novel small-molecule tools to efficiently label PMT substrates. Here we reported the development of a clickable SAM analogue cofactor, 4-propargyloxy-but-2-enyl SAM, and its implementation to label substrates of human protein arginine methyltransferase 1 (PRMT1). In the system, the SAM analogue cofactor, coupled with matched PRMT1 mutants rather than native PRMT1, was shown to label PRMT1 substrates. The transferable 4-propargyloxy-but-2-enyl moiety of the SAM analogue further allowed corresponding modified substrates to be characterized through a subsequent click chemical ligation with an azido-based probe. The SAM analogue, in combination with a rational protein-engineering approach, thus shows potential to label and identify PMT targets in the context of a complex cellular mixture.
Protein lysine methyltransferases (PKMTs) play crucial roles in normal physiology and disease processes. Profiling PKMT targets is an important but challenging task. With cancer-relevant G9a as a target, we have demonstrated success in developing S-adenosyl-L-methionine (SAM) analogues, particularly (E)-hex-2-en-5-ynyl SAM (Hey-SAM), as cofactors for engineered G9a. Hey-SAM analogue in combination with G9a Y1154A mutant modifies the same set of substrates as their native counterparts with remarkable efficiency. (E)-Hex-2-en-5-ynylated substrates undergo smooth click reaction with an azide-based probe. This approach is thus suitable for substrate characterization of G9a and expected to further serve as a starting point to evolve other PKMTs to utilize a similar set of cofactors.
Extracellular heat shock proteins (eHsps) in blood circulation have been associated with various diseases, including cancer. However, the lack of methods to enrich eHsps from serum samples has hampered the characterization of eHsps. This Letter presents our serendipitous finding that the monomeric avidin resin can serve as an affinity resin to enrich eHsps from blood serum. Biochemical mechanism of this eHsp enrichment as well as implications in biomarker discovery is discussed.
Reduced brain metabolism is an invariant feature of Alzheimer Disease (AD) that is highly correlated to the decline in brain functions. Decreased activities of key tricarboxylic acid cycle (TCA) cycle enzymes may underlie this abnormality and are highly correlated to the clinical state of the patient. The activity of the ?-ketoglutarate dehydrogenase complex (KGDHC), an arguably rate-limiting enzyme of the TCA cycle, declines with AD, but the mechanism of inactivation and whether it can be reversed remains unknown. KGDHC consists of multiple copies of three subunits. KGDHC is sensitive to oxidative stress, which is pervasive in AD brain. The present studies tested the mechanism for the peroxynitrite-induced inactivation and subsequent reactivation of purified and cellular KGDHC. Peroxynitrite inhibited purified KGDHC activity in a dose-dependent manner and reduced subunit immunoreactivity and increased nitrotyrosine immunoreactivity. Nano-LC-MS/MS showed that the inactivation was related to nitration of specific tyrosine residues in the three subunits. GSH diminished the nitrotyrosine immunoreactivity of peroxynitrite-treated KGDHC, restored the activity and the immunoreactivity for KGDHC. Nano-LC-MS/MS showed this was related to de-nitration of specific tyrosine residues, suggesting KGDHC may have a denitrase activity. Treatment of N2a cells with peroxynitrite for 5 min followed by recovery of cells for 24 h reduced KGDHC activity and increased nitrotyrosine immunoreactivity. Increasing cellular GSH in peroxynitrite-treated cells rescued KGDHC activity to the control level. The results suggest that restoring KGDHC activity is possible and may be a useful therapeutic approach in neurodegenerative diseases.
Activation-induced cytidine deaminase (AID) initiates immunoglobulin (Ig) heavy-chain (IgH) class switch recombination (CSR) and Ig variable region somatic hypermutation (SHM) in B lymphocytes by deaminating cytidines on template and nontemplate strands of transcribed DNA substrates. However, the mechanism of AID access to the template DNA strand, particularly when hybridized to a nascent RNA transcript, has been an enigma. We now implicate the RNA exosome, a cellular RNA-processing/degradation complex, in targeting AID to both DNA strands. In B lineage cells activated for CSR, the RNA exosome associates with AID, accumulates on IgH switch regions in an AID-dependent fashion, and is required for optimal CSR. Moreover, both the cellular RNA exosome complex and a recombinant RNA exosome core complex impart robust AID- and transcription-dependent DNA deamination of both strands of transcribed SHM substrates in vitro. Our findings reveal a role for noncoding RNA surveillance machinery in generating antibody diversity.
Proper bipolar attachment of sister kinetochores to the mitotic spindle is critical for accurate chromosome segregation in mitosis. Here we show an essential role of the formin mDia3 in achieving metaphase chromosome alignment. This function is independent of mDia3 actin nucleation activity, but is attributable to EB1-binding by mDia3. Furthermore, the microtubule binding FH2 domain of mDia3 is phosphorylated by Aurora B kinase in vitro, and cells expressing the nonphosphorylatable mDia3 mutant cannot position chromosomes at the metaphase plate. Purified recombinant mDia3 phosphorylated by Aurora B exhibits reduced ability to bind microtubules and stabilize microtubules against cold-induced disassembly in vitro. Cells expressing the phosphomimetic mDia3 mutant do not form stable kinetochore microtubule fibers; despite they are able to congress chromosomes to the metaphase plate. These findings reveal a key role for mDia3 and its regulation by Aurora B phosphorylation in achieving proper stable kinetochore microtubule attachment.
Protease inhibitor cocktails are routinely added to clinical samples used for proteomic studies to inactivate proteases. As these same samples are often used for microbial studies, we determined whether the addition of protease inhibitors could affect the quantitative or qualitative assessment of microbial profiles. Twenty-two saliva samples were collected and processed immediately with or without the addition of a protease inhibitor cocktail. Conventional cultivation methods were used to evaluate total bacterial growth. Total genomic DNA was isolated and a specific 16S rRNA gene-targeted region was PCR-amplified and separated by denaturing gradient gel electrophoresis. A combination of 1D sodium dodecyl sulfate polyacrylamide gel electrophoresis and LC-MS/MS methods was used to determine the effect of the protease inhibitors on the integrity of salivary proteins and peptides. Interestingly, no significant differences were observed in either the bacterial growth and composition or the integrity of salivary proteins between the two groups. Correlation coefficients between the paired samples for total cultivable microbiota (r(2) =0.847), total mutans streptococci (r(2) =0.898), total oral lactobacilli (r(2) =0.933), and total Streptococcus mutans (r(2) =0.870) also exceeded expected values. The results suggest that the addition of a protease inhibitor cocktail in saliva samples does not impact the growth of oral microbiota or compromise the ability to characterize its composition.
Rv3671c, a putative serine protease, is crucial for persistence of Mycobacterium tuberculosis in the hostile environment of the phagosome. We show that Rv3671c is required for M. tuberculosis resistance to oxidative stress in addition to its role in protection from acidification. Structural and biochemical analyses demonstrate that the periplasmic domain of Rv3671c is a functional serine protease of the chymotrypsin family and, remarkably, that its activity increases on oxidation. High-resolution crystal structures of this protease in an active strained state and in an inactive relaxed state reveal that a solvent-exposed disulfide bond controls the protease activity by constraining two distant regions of Rv3671c and stabilizing it in the catalytically active conformation. In vitro biochemical studies confirm that activation of the protease in an oxidative environment is dependent on this reversible disulfide bond. These results suggest that the disulfide bond modulates activity of Rv3671c depending on the oxidative environment in vivo.
An important function of the RNAase-III enzyme Dicer is to process microRNA precursors into ~22-nucleotide non-coding small RNAs. But little is known about the role of Dicer in mammalian brain formation and neural stem cell (NSC) development. Here we show that Dicer plays a crucial role in controlling mouse cortical NSC development. We found that Dicer function is essential for expanding cortical neural progenitors and NSCs. We have identified a population of Dicer-deficient NSCs that can self-renew, and that display normal karyotype and heterochromatin protein expression levels but show enlarged nuclei. Dicer-deficient NSCs display abnormal differentiation and undergo cell death when mitogens are withdrawn. Dicer deletion affects the levels of many proteins, as revealed by a mass spectrometry proteomic approach. We have found that an increase of anti-survival and/or pro-apoptosis proteins and a decrease of pro-survival and/or anti-apoptosis proteins contribute to the cell death of Dicer-deficient NSCs, implying a general role for Dicer in protecting cells from apoptosis. Our results demonstrate important functions for Dicer in regulating NSC development by maintaining proper signaling pathways related to cell survival and differentiation.
Many anti-infectives inhibit the synthesis of bacterial proteins, but none selectively inhibits their degradation. Most anti-infectives kill replicating pathogens, but few preferentially kill pathogens that have been forced into a non-replicating state by conditions in the host. To explore these alternative approaches we sought selective inhibitors of the proteasome of Mycobacterium tuberculosis. Given that the proteasome structure is extensively conserved, it is not surprising that inhibitors of all chemical classes tested have blocked both eukaryotic and prokaryotic proteasomes, and no inhibitor has proved substantially more potent on proteasomes of pathogens than of their hosts. Here we show that certain oxathiazol-2-one compounds kill non-replicating M. tuberculosis and act as selective suicide-substrate inhibitors of the M. tuberculosis proteasome by cyclocarbonylating its active site threonine. Major conformational changes protect the inhibitor-enzyme intermediate from hydrolysis, allowing formation of an oxazolidin-2-one and preventing regeneration of active protease. Residues outside the active site whose hydrogen bonds stabilize the critical loop before and after it moves are extensively non-conserved. This may account for the ability of oxathiazol-2-one compounds to inhibit the mycobacterial proteasome potently and irreversibly while largely sparing the human homologue.
Salvinorin A is the main active component of the widely available hallucinogenic plant, Salvia divinorum. Salvinorin A is a selective high-efficacy kappa-agonist in vitro, with some unique pharmacodynamic properties. Descriptive reports show that salvinorin A-containing products produce robust behavioral effects in humans. However, these effects have not been systematically characterized in human or nonhuman primates to date. Therefore, the present studies focused on the characterization of overt effects of salvinorin A, such as sedation (operationally defined as unresponsiveness to environmental stimuli) and postural relaxation, previously observed with centrally penetrating kappa-agonists in nonhuman primates. Salvinorin A was active in these endpoints (dose range, 0.01-0.1 mg/kg i.v.) in nonhuman primates (n = 3-5), similar to the synthetic kappa-agonist U69,593 [(+)-(5alpha,7alpha,8beta)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro[4.5]-dec-8-yl]-benzeneacetamide], used for comparison herein. Salvinorin A effects could be prevented by a clinically available opioid antagonist, nalmefene (0.1 mg/kg), at doses known to block kappa-receptor-mediated effects in nonhuman primates. When injected intravenously, salvinorin A (0.032 mg/kg) could enter the central nervous system (as reflected in cisternal cerebrospinal fluid) within 1 min and reach concentrations that are in the reported range of the affinity (K(i)) of this ligand for brain kappa-receptors. Consistent with this finding, specific translationally viable behavioral effects (e.g., facial relaxation and ptosis) could also be detected within 1 to 2 min of injection of salvinorin A. These are the first studies documenting rapid unconditioned effects of salvinorin A in a primate species, consistent with descriptive reports of rapid and robust effects of this powerful hallucinogen in humans.
Existing drugs are slow to eradicate Mycobacterium tuberculosis (Mtb) in patients and have failed to control tuberculosis globally. One reason may be that host conditions impair Mtbs replication, reducing its sensitivity to most antiinfectives. We devised a high-throughput screen for compounds that kill Mtb when its replication has been halted by reactive nitrogen intermediates (RNIs), acid, hypoxia, and a fatty acid carbon source. At concentrations routinely achieved in human blood, oxyphenbutazone (OPB), an inexpensive anti-inflammatory drug, was selectively mycobactericidal to nonreplicating (NR) Mtb. Its cidal activity depended on mild acid and was augmented by RNIs and fatty acid. Acid and RNIs fostered OPBs 4-hydroxylation. The resultant 4-butyl-4-hydroxy-1-(4-hydroxyphenyl)-2-phenylpyrazolidine-3,5-dione (4-OH-OPB) killed both replicating and NR Mtb, including Mtb resistant to standard drugs. 4-OH-OPB depleted flavins and formed covalent adducts with N-acetyl-cysteine and mycothiol. 4-OH-OPB killed Mtb synergistically with oxidants and several antituberculosis drugs. Thus, conditions that block Mtbs replication modify OPB and enhance its cidal action. Modified OPB kills both replicating and NR Mtb and sensitizes both to host-derived and medicinal antimycobacterial agents.
In the present work, we developed the Fc-III tagged protein expression system for protein purification and detection. The Fc-III sequence encodes for a 13 residue peptide and this peptide is cyclized by disulfide bond formation when the fusion protein is expressed. The Fc-III-fusion proteins selectively bind to immunoglobulin Fc domains (IgG-Fc) expressed from E. coli. We showed the efficient purification of Fc-III tagged proteins by immobilized non-native IgG-Fc and the detection of the cellular locations of fusion proteins by fluorescent-conjugated IgG-Fc. Our results prove that Fc-III tagged protein expression system is a simple and efficient tool for protein purification and detection and is a useful addition to the biochemistry and proteomics toolbox.
Posttranslational methylation by S-adenosyl-L-methionine(SAM)-dependent methyltransferases plays essential roles in modulating protein function in both normal and disease states. As such, there is a growing need to develop chemical reporters to examine the physiological and pathological roles of protein methyltransferases. Several sterically bulky SAM analogues have previously been used to label substrates of specific protein methyltransferases. However, broad application of these compounds has been limited by their general incompatibility with native enzymes. Here we report a SAM surrogate, ProSeAM (propargylic Se-adenosyl-l-selenomethionine), as a reporter of methyltransferases. ProSeAM can be processed by multiple protein methyltransferases for substrate labeling. In contrast, sulfur-based propargylic SAM undergoes rapid decomposition at physiological pH, likely via an allene intermediate. In conjunction with fluorescent/affinity-based azide probes, copper-catalyzed azide-alkyne cycloaddition chemistry, in-gel fluorescence visualization and proteomic analysis, we further demonstrated ProSeAMs utility to profile substrates of endogenous methyltransferases in diverse cellular contexts. These results thus feature ProSeAM as a convenient probe to study the activities of endogenous protein methyltransferases.
RCAN1, also known as DSCR1, is an endogenous regulator of calcineurin, a serine/threonine protein phosphatase that plays a critical role in many physiological processes. In this report, we demonstrate that p38? MAP kinase can phosphorylate RCAN1 at multiple sites in vitro and show that phospho-RCAN1 is a good protein substrate for calcineurin. In addition, we found that unphosphorylated RCAN1 noncompetitively inhibits calcineurin protein phosphatase activity and that the phosphorylation of RCAN1 by p38? MAP kinase decreases the binding affinity of RCAN1 for calcineurin. These findings reveal the molecular mechanism by which p38? MAP kinase regulates the function of RCAN1/calcineurin through phosphorylation.
Mass Spectrometry (MS) is becoming a preferred method to identify class I and class II peptides presented on major histocompability complexes (MHC) on antigen presenting cells (APC). We describe a combined computational and MS approach to identify exogenous MHC II peptides presented on mouse spleen dendritic cells (DCs). This approach enables rapid, effective screening of a large number of possible peptides by a computer-assisted strategy that utilizes the extraordinary human ability for pattern recognition. To test the efficacy of the approach, a mixture of epitope peptide mimics (mimetopes) from HIV gag p24 sequence were added exogenously to Fms-like tyrosine kinase 3 ligand (Flt3L)-mobilized splenic DCs. We identified the exogenously added peptide, VDRFYKTLRAEQASQ, and a second peptide, DRFYKLTRAEQASQ, derived from the original exogenously added 15-mer peptide. Furthermore, we demonstrated that our strategy works efficiently with HIV gag p24 protein when delivered, as vaccine protein, to Flt3L expanded mouse splenic DCs in vitro through the DEC-205 receptor. We found that the same MHC II-bound HIV gag p24 peptides, VDRFYKTLRAEQASQ and DRFYKLTRAEQASQ, were naturally processed from anti-DEC-205 HIV gag p24 protein and presented on DCs. The two identified VDRFYKTLRAEQASQ and DRFYKLTRAEQASQ MHC II-bound HIV gag p24 peptides elicited CD4(+) T-cell mediated responses in vitro. Their presentation by DCs to antigen-specific T cells was inhibited by chloroquine (CQ), indicating that optimal presentation of these exogenously added peptides required uptake and vesicular trafficking in mature DCs. These results support the application of our strategy to identify and characterize peptide epitopes derived from vaccine proteins processed by DCs and thus has the potential to greatly accelerate DC-based vaccine development.
Protein acetylation emerged as a key regulatory mechanism for many cellular processes. We used genetic analysis of Saccharomyces cerevisiae to identify Esa1 as a histone acetyltransferase required for autophagy. We further identified the autophagy signaling component Atg3 as a substrate for Esa1. Specifically, acetylation of K19 and K48 of Atg3 regulated autophagy by controlling Atg3 and Atg8 interaction and lipidation of Atg8. Starvation induced transient K19-K48 acetylation through spatial and temporal regulation of the localization of acetylase Esa1 and the deacetylase Rpd3 on pre-autophagosomal structures (PASs) and their interaction with Atg3. Attenuation of K19-K48 acetylation was associated with attenuation of autophagy. Increased K19-K48 acetylation after deletion of the deacetylase Rpd3 caused increased autophagy. Thus, protein acetylation contributes to control of autophagy.
Protein methyltransferases (PMTs) play critical roles in multiple biological processes. Because PMTs often function in vivo through forming multimeric protein complexes, dissecting their activities in the native contexts is challenging but relevant. To address such a need, we envisioned a Bioorthogonal Profiling of Protein Methylation (BPPM) technology, in which a SAM analogue cofactor can be utilized by multiple rationally engineered PMTs to label substrates of the corresponding native PMTs. Here, 4-azidobut-2-enyl derivative of S-adenosyl-L-methionine (Ab-SAM) was reported as a suitable BPPM cofactor. The resultant cofactor-enzyme pairs were implemented to label specifically the substrates of closely related PMTs (e.g., EuHMT1 and EuHMT2) in a complex cellular mixture. The BPPM approach, coupled with mass spectrometric analysis, enables the identification of the nonhistone targets of EuHMT1/2. Comparison of EuHMT1/2s methylomes indicates that the two human PMTs, although similar in terms of their primary sequences, can act on the distinct sets of nonhistone targets. Given the conserved active sites of PMTs, Ab-SAM and its use in BPPM are expected to be transferable to other PMTs for target identification.
The Arabidopsis thaliana protein UVR8 is a photoreceptor for ultraviolet-B. Upon ultraviolet-B irradiation, UVR8 undergoes an immediate switch from homodimer to monomer, which triggers a signalling pathway for ultraviolet protection. The mechanism by which UVR8 senses ultraviolet-B remains largely unknown. Here we report the crystal structure of UVR8 at 1.8?Å resolution, revealing a symmetric homodimer of seven-bladed ?-propeller that is devoid of any external cofactor as the chromophore. Arginine residues that stabilize the homodimeric interface, principally Arg?286 and Arg?338, make elaborate intramolecular cation-? interactions with surrounding tryptophan amino acids. Two of these tryptophans, Trp?285 and Trp?233, collectively serve as the ultraviolet-B chromophore. Our structural and biochemical analyses identify the molecular mechanism for UVR8-mediated ultraviolet-B perception, in which ultraviolet-B radiation results in destabilization of the intramolecular cation-? interactions, causing disruption of the critical intermolecular hydrogen bonds mediated by Arg?286 and Arg?338 and subsequent dissociation of the UVR8 homodimer.
The Beclin 1 gene is a haplo-insufficient tumor suppressor and plays an essential role in autophagy. However, the molecular mechanism by which Beclin 1 functions remains largely unknown. Here we report the crystal structure of the evolutionarily conserved domain (ECD) of Beclin 1 at 1.6 Å resolution. Beclin 1 ECD exhibits a previously unreported fold, with three structural repeats arranged symmetrically around a central axis. Beclin 1 ECD defines a novel class of membrane-binding domain, with a strong preference for lipid membrane enriched with cardiolipin. The tip of a surface loop in Beclin 1 ECD, comprising three aromatic amino acids, acts as a hydrophobic finger to associate with lipid membrane, consequently resulting in the deformation of membrane and liposomes. Mutation of these aromatic residues rendered Beclin 1 unable to stably associate with lipid membrane in vitro and unable to fully rescue autophagy in Beclin 1-knockdown cells in vivo. These observations form an important framework for deciphering the biological functions of Beclin 1.
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