title: Sulfopeptide fragmentation in electron-capture and electron-transfer dissociation.
abstract: Sulfopeptides can be misassigned as phosphopeptides because of the isobaric nature of the sulfo- and the phosphomoieties. Instruments having the ability to measure mass with high accuracy may be employed to distinguish these moieties based on their mass defect (the sulfo-group is 9 mmu lighter than the phosphomoiety). However, the assignment of the exact site(s) of post-translational modification is required to probe biological function. We have reported earlier that peptides with identical sequences containing either O-sulfo- or O-phospho-modifications display different fragmentation behavior (K. F. Medzihradszky et al., Mol. Cell. Proteom.2004, 3, 429-440). We have also established that O-sulfo moieties are susceptible to side-chain fragmentation during collision-induced dissociation. Our present study provides evidence that neutral SO(3) losses can also occur in electron capture dissociation and electron-transfer dissociation experiments. We also report that such neutral losses may be reduced by fragmenting peptide-alkali metal adducts, such as sodiated or potassiated peptides.
authors.affiliation: Mass Spectrometry Facility, Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California 94143-0446, USA. folkl@cgl.ucsf.edu
authors.forename: K F
authors.initials: KF
authors.lastname: Medzihradszky
authors.forename: S
authors.initials: S
authors.lastname: Guan
authors.forename: D A
authors.initials: DA
authors.lastname: Maltby
authors.forename: A L
authors.initials: AL
authors.lastname: Burlingame
mesh_terms: D004579:Electron Transport; D010748:Phosphopeptides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*; D013457:Sulfur Compounds / Q000737:chemistry*
chemical_list: D010748:Phosphopeptides; D013457:Sulfur Compounds