title: Screening for disulfide bonds in proteins by MALDI in-source decay and LIFT-TOF/TOF-MS.
abstract: An automated screening method is presented that uses MALDI in-source decay (MALDI-ISD) of disulfide bonds for identification of disulfide-linked peptides in MALDI mass spectra. Peptides released by ISD of a disulfide bond can be detected at an m/z ratio that corresponds to the singly protonated peptide with a reduced cysteine residue. Therefore, screening of peak lists for signal patterns that fulfill the equation, m/z (peak A) + m/z (peak B) - m/z (H2 + H+) = m/z (peak C), facilitated identification of putative ISD fragments of disulfide-linked peptides (peaks A and B) and their precursors (peak C). Signals (peak C) from putatively disulfide-linked peptides were subjected to LIFT-TOF/TOF-MS to confirm the existence of a disulfide bond. Using this method, we identified all 4 disulfide bonds in RNAseA and 8 two-disulfide clusters comprising 16 out of the 17 disulfide bonds in BSA. The presented screening method accelerated the identification of disulfide bonds in RNAseA and BSA, because the number of MS/MS spectra to be acquired was reduced by 1 order of magnitude. Less than 5% of the signals selected for LIFT-TOF/TOF-MS did not correspond to disulfide-linked peptides. Furthermore, the number of possible assignments for disulfide-linked peptides was reduced by 2-3 orders of magnitude, because knowledge of the mechanism of disulfide bond fragmentation by ISD permitted use of stricter rules for the interpretation of mass spectra. Therefore, interpretation of MS/ MS spectra of disulfide-linked peptides was considerably simplified in comparison to conventional approaches.
authors.affiliation: Center of Advanced European Studies and Research, Bonn, Germany. schnaible@caesar.de
authors.forename: Volker
authors.initials: V
authors.lastname: Schnaible
authors.forename: Stephan
authors.initials: S
authors.lastname: Wefing
authors.forename: Anja
authors.initials: A
authors.lastname: Resemann
authors.forename: Detlev
authors.initials: D
authors.lastname: Suckau
authors.forename: Anne
authors.initials: A
authors.lastname: Bücker
authors.forename: Sybille
authors.initials: S
authors.lastname: Wolf-Kümmeth
authors.forename: Daniel
authors.initials: D
authors.lastname: Hoffmann
mesh_terms: D000465:Algorithms; D002851:Chromatography, High Pressure Liquid; D004220:Disulfides / Q000032:analysis*; D007202:Indicators and Reagents; D013058:Mass Spectrometry; D010455:Peptides / Q000737:chemistry; D011492:Protein Hydrolysates / Q000737:chemistry; D011506:Proteins / Q000737:chemistry*; D012259:Ribonuclease, Pancreatic / Q000737:chemistry; D012710:Serum Albumin, Bovine / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D004220:Disulfides; D007202:Indicators and Reagents; D010455:Peptides; D011492:Protein Hydrolysates; D011506:Proteins; D012710:Serum Albumin, Bovine; D012259:Ribonuclease, Pancreatic