Amino acid influence on copper binding to peptides: cysteine versus arginine.
Matrix assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) and theoretical calculations [density functional theory (DFT)] were utilized to investigate the influence of cysteine side chain on Cu(+) binding to peptides and how Cu(+) ions competitively interact with cysteine (-SH/SO(3)H) versus arginine. Results from theoretical and experimental (fragmentation reactions) studies on [M + Cu](+) and [M + 2Cu - H](+) ions suggest that cysteine side chains (-SH) and cysteic acid (-SO(3)H) are important Cu(+) ligands. For example, we show that Cu(+) ions are competitively coordinated to the -SH or SO(3)H groups; however, we also present evidence that the proton of the SH/SO(3)H group is mobile and can be transferred to the arginine guanidine group. For [M + 2Cu - H](+) ions, deprotonation of the -SH/SO(3)H group is energetically more favorable than that of the carboxyl group, and the resulting thiolate/sulfonate group plays an important role in the coordination structure of [M + 2Cu - H](+) ions, as well as the fragmentation patterns.
Wu
Zhaoxiang
Z
Department of Chemistry, Texas A and M University, College Station, Texas 77843, USA.
Fernandez-Lima
Francisco A
FA
Russell
David H
DH
D001120:Arginine / Q000737:chemistry*; D003198:Computer Simulation; D003300:Copper / Q000737:chemistry*; D003545:Cysteine / Q000737:chemistry*; D008956:Models, Chemical; D010455:Peptides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
D010455:Peptides; D003300:Copper; D001120:Arginine; D003545:Cysteine