production-crystallization-structure-determination-c-difficile-ppep-1

Production, Crystallization and Structure Determination of <em>C. difficile</em> PPEP-1 via Microseeding and Zinc-SAD

New therapies are needed to treat Clostridium difficile infections that are a major threat to human health. The C. difficile metalloprotease PPEP-1 is a ...

University of Cologne

Archaemetzincins are metalloproteases occurring in archaea and some mammalia. They are distinct from all the other metzincins by their extended active site consensus sequence HEXXHXXGXXHCX(4)CXMX(17)CXXC featuring four conserved cysteine residues. Very little is known about their biological importance and structure-function relationships.

Crystal structures of archaemetzincin reveal a moldable substrate-binding site.

Murein recycling is a process in which microorganisms recover peptidoglycan-degradation products in order to utilize them in cell wall biosynthesis or basic metabolic pathways. Methanogens such as Methanopyrus kandleri contain pseudomurein, which differs from bacterial murein in its composition and branching. Here, four crystal structures of the putative sugar kinase MK0840 from M. kandleri in apo and nucleotide-bound states are reported. MK0840 shows high similarity to bacterial anhydro-N-acetylmuramic acid kinase, which is involved in murein recycling. The structure shares a common fold with panthothenate kinase and the 2-hydroxyglutaryl-CoA dehydratase component A, both of which are members of the ASKHA (acetate and sugar kinases/Hsc70/actin) superfamily of phosphotransferases. Local conformational changes in the nucleotide-binding site between the apo and holo forms are observed upon nucleotide binding. Further insight is given into domain movements and putative active-site residues are identified.

Structural characterization of the ribonuclease H-like type ASKHA superfamily kinase MK0840 from Methanopyrus kandleri.

The crystal structure of a truncated, soluble quadruple mutant of FtsH from Aquifex aeolicus comprising the AAA and protease domains has been determined at 2.96 Å resolution in space group I222. The protein crystallizes as a hexamer, with the protease domain forming layers in the ab plane. Contacts between these layers are mediated by the AAA domains. These are highly disordered in one crystal form, but are clearly visible in a related form with a shorter c axis. Here, adenosine diphosphate (ADP) is bound to each subunit and the AAA ring exhibits twofold symmetry. The arrangement is different from the ADP-bound state of an analogously truncated, soluble FtsH construct from Thermotoga maritima. The pore is completely closed and the phenylalanine residues in the pore line a contiguous path. The protease hexamer is very similar to those described for other FtsH structures. To resolve certain open issues regarding a conserved glycine in the linker between the AAA and protease domains, as well as the active-site switch β-strand, mutations have been introduced in the full-length membrane-bound protein. Activity analysis of these point mutants reveals the crucial importance of these residues for proteolytic activity and is in accord with previous interpretation of the active-site switch and the importance of the linker glycine residue.

The structure of Aquifex aeolicus FtsH in the ADP-bound state reveals a C2-symmetric hexamer.

Clostridium difficile is a pathogenic bacterium causing gastrointestinal diseases from mild diarrhea to toxic megacolon. In common with other pathogenic bacteria, C. difficile secretes proteins involved in adhesion, colonization, and dissemination. The recently identified Zmp1 is an extracellular metalloprotease showing a unique specificity for Pro-Pro peptide bonds. The endogenous substrates of Zmp1 are two surface proteins implicated in adhesion of C. difficile to surface proteins of human cells. Thus, Zmp1 is believed to be involved in the regulation of the adhesion-motility balance of C. difficile. Here, we report crystal structures of Zmp1 from C. difficile in its unbound and peptide-bound forms. The structure analysis revealed a fold similar to Bacillus anthracis lethal factor. Crystal structures in the open and closed conformation of the S-loop shed light on the mode of binding of the substrate, and reveal important residues for substrate recognition and the strict specificity of Zmp1 for Pro-Pro peptide bonds.

Structural Basis of Proline-Proline Peptide Bond Specificity of the Metalloprotease Zmp1 Implicated in Motility of Clostridium difficile.

The U32 family is a collection of over 2500 annotated peptidases in the MEROPS database with unknown catalytic mechanism. They mainly occur in bacteria and archaea, but a few representatives have also been identified in eukarya. Many of the U32 members have been linked to pathogenicity, such as proteins from Helicobacter and Salmonella. The first crystal structure analysis of a U32 catalytic domain from Methanopyrus kandleri (gene mk0906) reveals a modified (βα)8 TIM-barrel fold with some unique features. The connecting segment between strands β7 and β8 is extended and helix α7 is located on top of the C-terminal end of the barrel body. The protein exhibits a dimeric quaternary structure in which a zinc ion is symmetrically bound by histidine and cysteine side chains from both monomers. These residues reside in conserved sequence motifs. No typical proteolytic motifs are discernible in the three-dimensional structure, and biochemical assays failed to demonstrate proteolytic activity. A tunnel in which an acetate ion is bound is located in the C-terminal part of the β-barrel. Two hydrophobic grooves lead to a tunnel at the C-terminal end of the barrel in which an acetate ion is bound. One of the grooves binds to a Strep-Tag II of another dimer in the crystal lattice. Thus, these grooves may be binding sites for hydrophobic peptides or other ligands.

The first crystal structure of the peptidase domain of the U32 peptidase family.

Rho proteins are small GTP/GDP-binding proteins primarily involved in cytoskeleton regulation. Their GTP/GDP cycle is often tightly connected to a membrane/cytosol cycle regulated by the Rho guanine nucleotide dissociation inhibitor α (RhoGDIα). RhoGDIα has been regarded as a housekeeping regulator essential to control homeostasis of Rho proteins. Recent proteomic screens showed that RhoGDIα is extensively lysine-acetylated. Here, we present the first comprehensive structural and mechanistic study to show how RhoGDIα function is regulated by lysine acetylation. We discover that lysine acetylation impairs Rho protein binding and increases guanine nucleotide exchange factor-catalyzed nucleotide exchange on RhoA, these two functions being prerequisites to constitute a bona fide GDI displacement factor. RhoGDIα acetylation interferes with Rho signaling, resulting in alteration of cellular filamentous actin. Finally, we discover that RhoGDIα is endogenously acetylated in mammalian cells, and we identify CBP, p300, and pCAF as RhoGDIα-acetyltransferases and Sirt2 and HDAC6 as specific deacetylases, showing the biological significance of this post-translational modification.

Structural and Mechanistic Insights into the Regulation of the Fundamental Rho Regulator RhoGDIα by Lysine Acetylation.

Pathogenic bacteria secrete proteases to evade host defense and to acquire nutrients. In this issue of Structure, Arolas et al. (2016) describe the structural basis of activation and latency of InhA, a major secreted protease of Bacillus anthracis.

Feeding Anthrax: The Crystal Structure of Bacillus anthracis InhA Protease.

Sirtuins are NAD(+)-dependent lysine deacylases, regulating a variety of cellular processes. The nuclear Sirt1, the cytosolic Sirt2, and the mitochondrial Sirt3 are robust deacetylases, whereas the other sirtuins have preferences for longer acyl chains. Most previous studies investigated sirtuin-catalyzed deacylation on peptide substrates only. We used the genetic code expansion concept to produce natively folded, site-specific, and lysine-acetylated Sirt1-3 substrate proteins, namely Ras-related nuclear, p53, PEPCK1, superoxide dismutase, cyclophilin D, and Hsp10, and analyzed the deacetylation reaction. Some acetylated proteins such as Ras-related nuclear, p53, and Hsp10 were robustly deacetylated by Sirt1-3. However, other reported sirtuin substrate proteins such as cyclophilin D, superoxide dismutase, and PEPCK1 were not deacetylated. Using a structural and functional approach, we describe the ability of Sirt1-3 to deacetylate two adjacent acetylated lysine residues. The dynamics of this process have implications for the lifetime of acetyl modifications on di-lysine acetylation sites and thus constitute a new mechanism for the regulation of proteins by acetylation. Our studies support that, besides the primary sequence context, the protein structure is a major determinant of sirtuin substrate specificity.

Article	Year
Crystal structures of archaemetzincin reveal a moldable substrate-binding site. PloS one\| PubMed ID: 22937112	2012
Structural characterization of the ribonuclease H-like type ASKHA superfamily kinase MK0840 from Methanopyrus kandleri. Acta crystallographica. Section D, Biological crystallography\| PubMed ID: 24311585	2013
The structure of Aquifex aeolicus FtsH in the ADP-bound state reveals a C2-symmetric hexamer. Acta crystallographica. Section D, Biological crystallography\| PubMed ID: 26057670	2015
Structural Basis of Proline-Proline Peptide Bond Specificity of the Metalloprotease Zmp1 Implicated in Motility of Clostridium difficile. Structure (London, England : 1993)\| PubMed ID: 26211609	2015
The first crystal structure of the peptidase domain of the U32 peptidase family. Acta crystallographica. Section D, Biological crystallography\| PubMed ID: 26627657	2015
Structural and Mechanistic Insights into the Regulation of the Fundamental Rho Regulator RhoGDIα by Lysine Acetylation. The Journal of biological chemistry\| PubMed ID: 26719334	2016
Feeding Anthrax: The Crystal Structure of Bacillus anthracis InhA Protease. Structure (London, England : 1993)\| PubMed ID: 26745525	2016
Insights into Lysine Deacetylation of Natively Folded Substrate Proteins by Sirtuins. The Journal of biological chemistry\| PubMed ID: 27226597	2016

Magdalena Schacherl

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