title: Identification of a novel proteoform of prostate specific antigen (SNP-L132I) in clinical samples by multiple reaction monitoring.
abstract: Prostate specific antigen (PSA) is a well-established tumor marker that is frequently employed as model biomarker in the development and evaluation of emerging quantitative proteomics techniques, partially as a result of wide access to commercialized immunoassays serving as "gold standards." We designed a multiple reaction monitoring (MRM) assay to detect PSA proteoforms in clinical samples (n = 72), utilizing the specificity and sensitivity of the method. We report, for the first time, a PSA proteoform coded by SNP-L132I (rs2003783) that was observed in nine samples in both heterozygous (n = 7) and homozygous (n = 2) expression profiles. Other isoforms of PSA, derived from protein databases, were not identified by four unique proteotypic tryptic peptides. We have also utilized our MRM assay for precise quantitative analysis of PSA concentrations in both seminal and blood plasma samples. The analytical performance was evaluated, and close agreement was noted between quantitations based on three selected peptides (LSEPAELTDAVK, IVGGWECEK, and SVILLGR) and a routinely used commercialized immunoassay. Additionally, we disclose that the peptide IVGGWECEK is shared with kallikrein-related peptidase 2 and therefore is not unique for PSA. Thus, we propose the use of another tryptic sequence (SVILLGR) for accurate MRM quantification of PSA in clinical samples.
authors.affiliation: Clinical Protein Science & Imaging, Biomedical Center, Dept. of Measurement Technology and Industrial Electrical Engineering, Lund University, BMC C13, 221 84 Lund, Sweden;
authors.forename: Akos
authors.initials: A
authors.lastname: Végvári
authors.forename: Karin
authors.initials: K
authors.lastname: Sjödin
authors.forename: Melinda
authors.initials: M
authors.lastname: Rezeli
authors.forename: Johan
authors.initials: J
authors.lastname: Malm
authors.forename: Hans
authors.initials: H
authors.lastname: Lilja
authors.forename: Thomas
authors.initials: T
authors.lastname: Laurell
authors.forename: György
authors.initials: G
authors.lastname: Marko-Varga
mesh_terms: D001681:Biological Assay; D014408:Biomarkers, Tumor / Q000032:analysis* / Q000737:chemistry / Q000235:genetics; D006801:Humans; D008297:Male; D009842:Oligopeptides / Q000032:analysis* / Q000235:genetics; D010949:Plasma / Q000737:chemistry; D020641:Polymorphism, Single Nucleotide; D017430:Prostate-Specific Antigen / Q000032:analysis* / Q000737:chemistry / Q000235:genetics; D011471:Prostatic Neoplasms / Q000175:diagnosis* / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms; D012661:Semen / Q000737:chemistry
chemical_list: D014408:Biomarkers, Tumor; D009842:Oligopeptides; D020033:Protein Isoforms; D017430:Prostate-Specific Antigen