Cu(I) binding to the Schizosaccharomyces pombe gamma-glutamyl peptides varying in chain lengths.

Abstract

The metal-gamma-glutamyl peptide complex of Schizosaccharomyces pombe is an oligomer of peptides of the general structure (gamma-Glu-Cys)n-Gly with n defining the number of dipeptide repeats. The complexes induced with either cadmium or copper salts are heterogeneous with respect to the number of repeat units or n. Peptides isolated from two preparations of the Cd-gamma-Glu complex by reverse-phase HPLC at low pH were of an n range of 2 to 6 with n3 and n4 peptides being predominant. In addition to peptides of the mentioned structure, peptides of n3 and n4 without the terminal Gly were isolated. These n3 and n4 desGly peptides were present in an abundance of about 10-20% of the concentration of the parent peptide. Peptides of unique n were studied in Cu(I) reconstitution experiments in an attempt to understand the significance of the peptide length heterogeneity in the oligomeric metal-thiolate cluster. Cu-gamma-Glu complexes were formed with each peptide as determined by the characteristic 260-nm shoulder in the ultraviolet absorption spectrum and luminescence indicative of Cu(I)-thiolate coordination in a solvent-inaccessible environment. Cluster formation also occurs with desGly peptides, so the carboxyl-terminal Gly is not critical for cluster formation. Maximal Cu binding stoichiometry with n3 and n4 peptides was markedly less than the maximal Cu(I) stoichiometry of a peptide mixture or the native complex. Cu ions in complexes formed with unique n peptides were more reactive with bathocuproine than Cu ions in complexes with a peptide n mixture. The results suggest that metal-peptide complexes consisting of peptides differing in n probably exist and not all metal-peptide complexes have the same n peptide constituents.