Redox activity and multiple copper(I) coordination of 2His-2Cys oligopeptide.

Copper binding motifs with their molecular mechanisms of selective copper(I) recognition are essential molecules for acquiring copper ions, trafficking copper to specific locations and controlling the potentially damaging redox activities of copper in biochemical processes. The redox activity and multiple Cu(I) binding of an analog methanobactin peptide-2 (amb2) with the sequence acetyl-His1-Cys2-Tyr3-Pro4-His5-Cys6 was investigated using ion mobility-mass spectrometry (IM-MS) and UV-Vis spectrophotometry analyses. The Cu(II) titration of amb2 showed oxidation of amb2 via the formation of intra- and intermolecular Cys-Cys disulfide bridges and the multiple Cu(I) coordination by unoxidized amb2 or the partially oxidized dimer and trimer of amb2. The principal product of these reactions was [amb2 + 3Cu(I)](+) which probably coordinates the three Cu(I) ions via two bridging thiolate groups of Cys2 and Cys6 and the δN6 of the imidazole groups of His6, as determined by geometry optimized structures at the B3LYP/LanL2DZ level of theory. The products observed by IM-MS showed direct correlation to spectral changes associated with disulfide bond formation in the UV-Vis spectrophotometric study. The results show that IM-MS analysis is a powerful technique for unambiguously determining the major ion species produced during the redox and metal binding chemistry of oligopeptides.