PH dependent chelation study of Zn(II) and Ni(II) by a series of hexapeptides using electrospray ionization – Ion mobility – Mass spectrometry

Abstract

Presented here are the results of a study characterizing the selective metal chelating performance of the alternative metal binding (amb) peptide: acetyl-His1-Cys2-Gly3-Pro4-His5-Cys6-OH, and eight ambs with systematic modifications to His, Cys, and carboxyl C-terminus metal chelating sites. The results show that from the divalent metal ions of zinc, nickel, cobalt, magnesium and calcium, the ambs most extensively formed complexes with zinc and nickel. The ambs, which retained both Cys2 and Cys6 in their primary structure, exhibited the greatest formation of zinc complexes. The replacement of His1 and His5 residues with two additional Cys with the amidation of the C-terminus also increased the zinc chelation at pH 7.0. Density functional theory indicated that these modifications might be disrupting the hydrogen bonding between the His-Cys and carboxylate terminus making the 4Cys more available for chelation. Nickel chelation was generally lower than zinc because of competition from the Cys to form disulfide bonds in the presence of nickel. The two ambs that formed the highest number of nickel complexes both included the amidated C-termini and either 4Cys or 2Cys-2His. Comparison with recent published results of six heptapeptide ambs, which have the same primary structures, but with the inclusion of Tyr5 before the final two residues, indicates the inclusion of the Tyr5 residue increases the zinc chelation at pH 7.0 from 25%, of total observed species, to 70%. These types of studies may pave the way to discoveries of new therapeutics suitable as enzyme inhibitors or chelators for diseases associated with metal homeostasis misbalances, or as new peptide tags for recombinant protein purification.