title: Mass spectrometry characterization of the thermal decomposition/digestion (TDD) at cysteine in peptides and proteins in the condensed phase.
abstract: We report on the characterization by mass spectrometry (MS) of a rapid, reagentless and site-specific cleavage at the N-terminus of the amino acid cysteine (C) in peptides and proteins induced by the thermal decomposition at 220-250 °C for 10 s in solid samples. This thermally induced cleavage at C occurs under the same conditions and simultaneously to our previously reported thermally induced site-specific cleavage at the C-terminus of aspartic acid (D) (Zhang, S.; Basile, F. J. Proteome Res. 2007, 6, (5), 1700-1704). The C cleavage proceeds through cleavage of the nitrogen and α-carbon bond (N-terminus) of cysteine and produces modifications at the cleavage site with an amidation (-1 Da) of the N-terminal thermal decomposition product and a -32 Da mass change of the C-terminal thermal decomposition product, the latter yielding either an alanine or β-alanine residue at the N-terminus site. These modifications were confirmed by off-line thermal decomposition electrospray ionization (ESI)-MS, tandem MS (MS/MS) analyses and accurate mass measurements of standard peptides. Molecular oxygen was found to be required for the thermal decomposition and cleavage at C as it induced an initial cysteine thiol side chain oxidation to sulfinic acid. Similar to the thermally induced D cleavage, missed cleavages at C were also observed. The combined thermally induced digestion process at D and C, termed thermal decomposition/digestion (TDD), was observed on several model proteins tested under ambient conditions and the site-specificity of the method confirmed by MS/MS.
authors.affiliation: Department of Chemistry, University of Wyoming, 1000 University Ave., Laramie, WY 82071, USA. basile@uwyo.edu
authors.forename: Franco
authors.initials: F
authors.lastname: Basile
authors.forename: Shaofeng
authors.initials: S
authors.lastname: Zhang
authors.forename: Sujit Kumar
authors.initials: SK
authors.lastname: Kandar
authors.forename: Liang
authors.initials: L
authors.lastname: Lu
mesh_terms: D000595:Amino Acid Sequence; D002384:Catalysis; D003545:Cysteine / Q000737:chemistry*; D006358:Hot Temperature; D008969:Molecular Sequence Data; D010100:Oxygen / Q000737:chemistry; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism; D010449:Peptide Mapping / Q000379:methods*; D011506:Proteins / Q000737:chemistry / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D053719:Tandem Mass Spectrometry / Q000379:methods*; D014357:Trypsin / Q000378:metabolism
chemical_list: D010446:Peptide Fragments; D011506:Proteins; D014357:Trypsin; D003545:Cysteine; D010100:Oxygen