title: Neutral loss of isocyanic acid in peptide CID spectra: a novel diagnostic marker for mass spectrometric identification of protein citrullination.
abstract: Protein citrullination is emerging as an important signaling mechanism that modulates a variety of biological processes. This protein modification constitutes only a 1 Da mass shift, and can be readily confused with other common protein modifications that yield an identical mass shift. In an attempt to develop a robust methodology for detection of protein citrullination sites, we analyzed synthetic citrulline-containing peptides by electrospray ionization tandem mass spectrometry. Collision-induced dissociation (CID) spectra revealed abundant neutral loss of 43 Da from citrullinated peptide precursor ions, which was reconciled by elimination of the HNCO moiety (isocyanic acid) from the citrulline ureido group. The elimination occurs readily in multiple charge states of precursor ions and also in b and y ions. HNCO loss in CID spectra provides a novel diagnostic marker for citrullination, and its utility was demonstrated by the discovery of Arg197 as the specific site of citrullination on nucleophosmin upon peptidylarginine deiminase 4 treatment.
authors.affiliation: Department of Pharmacology, Weill Medical College of Cornell University, New York, New York, USA.
authors.forename: Gang
authors.initials: G
authors.lastname: Hao
authors.forename: Danchen
authors.initials: D
authors.lastname: Wang
authors.forename: Jane
authors.initials: J
authors.lastname: Gu
authors.forename: Qiuying
authors.initials: Q
authors.lastname: Shen
authors.forename: Steven S
authors.initials: SS
authors.lastname: Gross
authors.forename: Yanming
authors.initials: Y
authors.lastname: Wang
mesh_terms: D002853:Chromatography, Liquid; D002956:Citrulline / Q000737:chemistry*; D003485:Cyanates / Q000737:chemistry*; D006801:Humans; D006867:Hydrolases; D009687:Nuclear Proteins; D000090243:Nucleophosmin; D010455:Peptides / Q000737:chemistry*; D011499:Protein Processing, Post-Translational; D000080002:Protein-Arginine Deiminase Type 4; D000076342:Protein-Arginine Deiminases; D053719:Tandem Mass Spectrometry
chemical_list: D003485:Cyanates; C000716967:NPM1 protein, human; D009687:Nuclear Proteins; D010455:Peptides; D000090243:Nucleophosmin; D002956:Citrulline; D006867:Hydrolases; C000629235:PADI4 protein, human; D000080002:Protein-Arginine Deiminase Type 4; D000076342:Protein-Arginine Deiminases; C005057:isocyanic acid