title: Effect of structural parameters of peptides on dimer formation and highly oxidized side products in the oxidation of thiols of linear analogues of human beta-defensin 3 by DMSO.
abstract: The purpose of this study was to examine the effects of structural parameters of peptides on their oxidation by DMSO, including location of cysteine, effect of adjunct group participation, molecular hydrophobicity, steric hindrance or the accessibility of thiol group and peptide conformation, on oxidation rates, dimer formation and associated side products. We designed and synthesized two series of linear cysteine-containing analogues of human beta-defensin 3 (the C1-peptides with cysteine at the N-terminus residue 1, the C29-peptides with cysteine located at residue 29 in the centre of peptide), which were used for preparation of disulphide-linked homodimers. HPLC-ESI-MS was used to monitor the oxidation process and to characterize the molecular weights of dimers and side products of high oxidation. The formations of dimers and side products were dependent on the position of cysteines. Hydrophobicity generally rendered the thiol groups less accessible and hence exposed them to slow oxidation to form dimers (or even fail to form dimers during the timescale of observation). Molecular dynamics simulations showed that the exposure of cysteines (and sulphurs) of the C1-peptides was much larger than for the C29-peptides. The larger hydrophobic side chains tended to enable clustering of the side chains that sequester cysteine, particularly in the C29-peptides, which provided a molecular explanation for the observed trends in oxidation rates. Together with molecular modelling, we propose a reaction mechanism to elucidate the oxidation results of these peptides.
authors.affiliation: Singapore Eye Research Institute, Singapore.
authors.forename: Shouping
authors.initials: S
authors.lastname: Liu
authors.forename: Lei
authors.initials: L
authors.lastname: Zhou
authors.forename: Liyan
authors.initials: L
authors.lastname: Chen
authors.forename: Shubhra Ghosh
authors.initials: SG
authors.lastname: Dastidar
authors.forename: Chandra
authors.initials: C
authors.lastname: Verma
authors.forename: Jing
authors.initials: J
authors.lastname: Li
authors.forename: Donald
authors.initials: D
authors.lastname: Tan
authors.forename: Roger
authors.initials: R
authors.lastname: Beuerman
mesh_terms: D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003545:Cysteine / Q000737:chemistry; D019281:Dimerization; D004121:Dimethyl Sulfoxide / Q000737:chemistry*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry* / Q000235:genetics; D020836:Protein Structure, Quaternary; D012997:Solvents / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D023083:beta-Defensins / Q000737:chemistry* / Q000235:genetics
chemical_list: C422950:DEFB103A protein, human; D010455:Peptides; D012997:Solvents; D013438:Sulfhydryl Compounds; D023083:beta-Defensins; D003545:Cysteine; D004121:Dimethyl Sulfoxide