title: Electron transfer dissociation mass spectrometry of peptides containing free cysteine using group XII metals as a charge carrier.
abstract: Electron transfer dissociation (ETD) has been used for peptide sequencing. Since ETD preferentially produces the c'/z(•) fragment pair, peptide sequencing is generally performed by interpretation of mass differences between series of consecutive c' and z(•) ions. However, the presence of free cysteine residues in a precursor promotes peptide bond cleavage, hindering interpretation of the ETD spectrum. In the present study, the divalent group XII metals, such as Zn(2+), Cd(2+) and Hg(2+), were used as charge carriers to produce metal-peptide complexes. The thiol group is deprotonated by complexation with the group XII metal. The formation of b and y' ions was successfully suppressed by using the zinc-peptide complex as a precursor, indicating Zn(2+)-aided ETD to be a useful method for sequencing of cysteine-containing peptides. By contrast, ETD of Cd(2+)- and Hg(2+)-peptide complexes mainly led to SH2 loss and radical cation formation, respectively. These processes were mediated by recombination energy between the metal cation and an electron. The presence of monovalent cadmium and neutral mercury in ETD products was confirmed by MS(3) analysis with collision-induced dissociation.
authors.affiliation: Department of Molecular Medicine, Osaka Medical Center and Research Institute for Maternal and Child Health , 840 Murodo-cho, Izumi, Osaka 594-1101, Japan.
authors.forename: Daiki
authors.initials: D
authors.lastname: Asakawa
authors.forename: Yoshinao
authors.initials: Y
authors.lastname: Wada
mesh_terms: D000595:Amino Acid Sequence; D003545:Cysteine / Q000737:chemistry*; D004579:Electron Transport; D013058:Mass Spectrometry; D019216:Metals, Heavy / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry*
chemical_list: D019216:Metals, Heavy; D010455:Peptides; D003545:Cysteine