title: Cyclophosphoramidate ion as mass defect marker for efficient detection of protein serine phosphorylation.
abstract: A novel method is reported to modify the phosphate groups on phosphoserine peptides to the corresponding phosphoramidates, using 2-aminobenzylamine. Upon collision-induced dissociation, the modified peptides release the positively charged phosphoramidate that via gas-phase intramolecular elimination forms a cyclophosphoramidate (CyPAA) ion, the protonated form of 1,4-dihydro-2-hydroxy-2-oxobenzo[3,1,2]oxazaphosphorine. The positive nature of the ion eliminates the need for real-time instrument polarity switching and greatly increases the versatility of commonly used mass spectrometers for phosphopeptide analysis. This ion has sufficient mass defect, due to containing a phosphorus atom and a high content of oxygen atoms, which makes mass spectrometers of medium mass resolution and accuracy adequate for separating the ion from isobaric interfering ions. The specificity of the CyPAA ion for detecting phosphoserine peptides in complex peptide mixtures is comparable to the specificity of the phosphotyrosine immonium ion for phosphotyrosine peptides, allowing the efficient data complexity reduction for fast and focused analysis of phosphoserine-containing peptides.
authors.affiliation: Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269, USA.
authors.forename: Yu
authors.initials: Y
authors.lastname: Shi
authors.forename: Bekim
authors.initials: B
authors.lastname: Bajrami
authors.forename: Martha
authors.initials: M
authors.lastname: Morton
authors.forename: Xudong
authors.initials: X
authors.lastname: Yao
mesh_terms: D000577:Amides / Q000737:chemistry*; D000818:Animals; D045424:Complex Mixtures / Q000032:analysis; D010750:Phosphoproteins / Q000032:analysis* / Q000737:chemistry; D010756:Phosphoric Acids / Q000737:chemistry*; D010766:Phosphorylation; D010768:Phosphoserine / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry; D011506:Proteins / Q000032:analysis; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D000577:Amides; D045424:Complex Mixtures; D010750:Phosphoproteins; D010756:Phosphoric Acids; D011506:Proteins; D010768:Phosphoserine; C011067:phosphoramidic acid