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Articles by Matthew E. Pope in JoVE
JoVE General
Kwantificering van eiwitten met behulp van immuno-peptide Verrijking gekoppeld aan massaspectrometrie
1Clinical Research Division, Fred Hutchinson Cancer Research Center - FHCRC, 2Department of Biochemistry and Microbiology, University of Victoria, 3Broad Institute of MIT and Harvard, 4Genome BC Proteomics Centre, University of Victoria, 5Plasma Proteome Institute
Stabiele Isotopen Normen en Capture door Anti-peptide antilichamen (SISCAPA) paren affiniteit verrijking van peptiden met stabiele isotoop verdunning massaspectrometrie (MRM-MS) voor kwantitatieve meting van peptiden te bieden als surrogaat voor hun respectievelijke eiwitten. Hier beschrijven we het protocol met behulp van magnetische deeltjes in een deels geautomatiseerde formaat.
Other articles by Matthew E. Pope on PubMed
Anti-peptide Antibody Screening: Selection of High Affinity Monoclonal Reagents by a Refined Surface Plasmon Resonance Technique
A refined surface plasmon resonance method was developed to measure the kinetics of peptide binding to rabbit monoclonal antibodies (RabMAbs). Optimized amounts of RabMAbs were captured onto sensor chips from hybridoma supernatants followed by binding of free peptides from solution. This allowed kinetic measurement of monovalent interactions of peptides with single antigen binding sites on the antibodies and determination of affinity constants without complications contributed by avidity considerations. Peptide-binding responses were normalized for the amount of antibody present in each sample and a simple interaction model was fit to all of the binding responses simultaneously. As a result, the kinetic rate constants ka and kd, and the affinity constant KD (kd/ka), could be determined for each antibody interaction under identical conditions. Higher-resolution studies involving multiple concentrations of peptide antigens were performed to validate the reliability of single-concentration measurements. By combining data on affinity, activity and concentration, ranking of the antibody-containing supernatants was performed, allowing selection of high quality RabMAbs for binding of peptides in solution.
MALDI Immunoscreening (MiSCREEN): a Method for Selection of Anti-peptide Monoclonal Antibodies for Use in Immunoproteomics
A scalable method for screening and selection of peptide-specific monoclonal antibodies (mAbs) is described. To identify high affinity anti-peptide mAbs in hybridoma supernatants, antibodies were captured by magnetic affinity beads followed by binding of specific peptides from solution. After timed washing steps, the remaining bound peptides were eluted from the beads and detected by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS). This allowed measurement of monovalent interactions of peptides with single antigen binding sites on the antibodies, thus reflecting antibody affinity rather than avidity. Antibodies that were able to bind target peptides from solution phase and retain them during washing for a minimum of 10 min were identified by the strength of the appropriate m/z peptide MS signals obtained. This wash time reflects the minimum peptide dissociation time required for use of these antibodies in several current immuno-mass spectrometry assays. Kinetic analysis of antibody-peptide binding by surface plasmon resonance (SPR) showed that the selected antibodies were of high affinity and, most importantly, had low dissociation constants. This method, called MALDI immunoscreening (MiSCREEN), thus enables rapid screening and selection of high affinity anti-peptide antibodies that are useful for a variety of immunoproteomics applications. To demonstrate their functional utility in immuno-mass spectrometry assays, we used the selected, purified RabMAbs to enrich natural (tryptic) peptides from digested human plasma.
Evaluation of Large Scale Quantitative Proteomic Assay Development Using Peptide Affinity-based Mass Spectrometry
Stable isotope standards and capture by antipeptide antibodies (SISCAPA) couples affinity enrichment of peptides with stable isotope dilution and detection by multiple reaction monitoring mass spectrometry to provide quantitative measurement of peptides as surrogates for their respective proteins. In this report, we describe a feasibility study to determine the success rate for production of suitable antibodies for SISCAPA assays in order to inform strategies for large-scale assay development. A workflow was designed that included a multiplex immunization strategy in which up to five proteotypic peptides from a single protein target were used to immunize individual rabbits. A total of 403 proteotypic tryptic peptides representing 89 protein targets were used as immunogens. Antipeptide antibody titers were measured by ELISA and 220 antipeptide antibodies representing 89 proteins were chosen for affinity purification. These antibodies were characterized with respect to their performance in SISCAPA-multiple reaction monitoring assays using trypsin-digested human plasma matrix. More than half of the assays generated were capable of detecting the target peptide at concentrations of less than 0.5 fmol/μl in human plasma, corresponding to protein concentrations of less than 100 ng/ml. The strategy of multiplexing five peptide immunogens was successful in generating a working assay for 100% of the targeted proteins in this evaluation study. These results indicate it is feasible for a single laboratory to develop hundreds of assays per year and allow planning for cost-effective generation of SISCAPA assays.
Inter-laboratory Evaluation of Automated, Multiplexed Peptide Immunoaffinity Enrichment Coupled to Multiple Reaction Monitoring Mass Spectrometry for Quantifying Proteins in Plasma
The inability to quantify large numbers of proteins in tissues and biofluids with high precision, sensitivity and throughput is a major bottleneck in biomarker studies. We previously demonstrated that coupling immunoaffinity enrichment using anti-peptide antibodies (SISCAPA) to MRM-MS produces immuno-MRM assays that can be multiplexed to quantify proteins in plasma with high sensitivity, specificity, and precision. Here we report the first systematic evaluation of the inter-laboratory performance of multiplexed (8-plex) immuno-MRM-MS in three independent labs. A staged study was carried out in which the effect of each processing and analysis step on assay CV, LOD, LOQ and recovery was evaluated. Limits of detection were at or below 1 ng/mL for the assayed proteins in 30 uL of plasma. Assay reproducibility was acceptable for verification studies, with median intra- and inter-laboratory CVs above the LOQ of 11% and <14%, respectively, for the entire immuno-MRM-MS assay process, including enzymatic digestion of plasma. Trypsin digestion and its requisite sample handling contributed the most to assay variability and reduced the recovery of target peptides from digested proteins. Using a stable isotope labeled protein as an internal standard instead of stable isotope labeled peptides to account for losses in the digestion process nearly doubled assay accuracy for this while improving assay precision 5%. Our results demonstrate that multiplexed immuno-MRM-MS can be made reproducible across independent laboratories and has the potential to be adopted widely for assaying proteins in matrices as complex as plasma.
