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 His_6, 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. Copyright © 2015 John Wiley & Sons, Ltd.     

The multiple conformational charge states of zinc(II) coordination by 2His‐2Cys oligopeptide investigated by ion mobility‐mass spectrometry,density functional theory and theoretical collision cross sections

Whether traveling wave ion mobility‐mass spectrometry (IM‐MS), B3LYP/LanL2DZ density functional theory, and ion size scaled Lennard‐Jones (LJ) collision cross sections (CCS) from the B3LYP optimized structures could be used to determine the type of Zn(II) coordination by the oligopeptide acetyl‐His₁‐Cys₂‐Gly₃‐Pro₄‐Tyr₅‐His₆‐Cys₇ (amb₅) was investigated. The IM‐MS analyses of a pH titration of molar equivalents of Zn(II):amb₅ showed that both negatively and positively charged complexes formed and coordination of Zn(II) increased as the His and Cys deprotonated near their pKa values. The B3LYP method was used to generate a series of alternative coordination structures to compare with the experimental results. The method predicted that the single negatively charged complex coordinated Zn(II) in a distorted tetrahedral geometry via the 2His‐2Cys substituent groups, whereas, the double negatively charged and positively charged complexes coordinated Zn(II) via His, carbonyl oxygens and the C‐terminus. The CCS of the B3LYP complexes were calculated using the LJ method and compared with those measured by IM‐MS for the various charge state complexes. The LJ method provided CCS that agreed with five of the alternative distorted tetrahedral and trigonal bipyramidal coordinations for the doubly charged complexes, but provided CCS that were 15 to 31 Ų larger than those measured by IM‐MS for the singly charged complexes. Collision‐induced dissociation of the Zn(II) complexes and a further pH titration study of amb_5B, which included amidation of the C‐terminus, suggested that the 2His‐2Cys coordination was more significant than coordinations that included the C‐terminus. Copyright © 2016 John Wiley & Sons, Ltd.