title: Desulfurization of cysteine-containing peptides resulting from sample preparation for protein characterization by mass spectrometry.
abstract: In this study, we have examined two cysteine modifications resulting from sample preparation for protein characterization by mass spectrometry (MS): (1) a previously observed conversion of cysteine into dehydroalanine, now found in the case of disulfide mapping and (2) a novel modification corresponding to conversion of cysteine into alanine. Using model peptides, the conversion of cysteine into dehydroalanine via beta-elimination of a disulfide bond was seen to result from the conditions of typical tryptic digestion (37 degrees C, pH 7.0-9.0) without disulfide reduction and alkylation. Furthermore, the surprising conversion of cysteine into alanine was shown to occur by heating cysteine-containing peptides in the presence of a phosphine (tris(2-carboxyethyl)phosphine hydrochloride (TCEP)). The formation of alanine from cysteine, investigated by performing experiments in H(2)O or D(2)O, suggested a radical-based desulfurization mechanism unrelated to beta-elimination. Importantly, an understanding of the mechanism and conditions favorable for cysteine desulfurization provides insight for the establishment of improved sample preparation procedures of protein analysis.
authors.affiliation: Barnett Institute and Department of Chemistry and Chemical Biology, Northeastern University, Boston, MA 02115, USA.
authors.forename: Zhouxi
authors.initials: Z
authors.lastname: Wang
authors.forename: Tomas
authors.initials: T
authors.lastname: Rejtar
authors.forename: Zhaohui Sunny
authors.initials: ZS
authors.lastname: Zhou
authors.forename: Barry L
authors.initials: BL
authors.lastname: Karger
mesh_terms: D000409:Alanine / Q000737:chemistry / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry* / Q000378:metabolism; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D013058:Mass Spectrometry / Q000379:methods*; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D011506:Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D004220:Disulfides; D010455:Peptides; D011506:Proteins; D003545:Cysteine; D000409:Alanine