NMR DETERMINATION OF THE STRUCTURES OF PEROXYCOBALT(III) BLEOMYCIN AND COBALT(III) BLEOMYCIN, PRODUCTS OF THE AEROBIC OXIDATION OF COBALT(II) BLEOMYCIN BY DIOXYGEN

The oxidation of Co(II)bleomycin A2 by dioxygen leads to two products, HO2-Co(III)bleomycin A2 (form I) and Co(III)bleomycin A2 (form II). H-1 NMR chemical shift assignments for protons of both forms have been made by two-dimensional NMR spectral techniques. The chemical shifts of protons throughout forms I and II differ from each other and from apobleomycin A2. NOESY spectra reveal a number of intermediate and long-range H-1-H-1 couplings within the metal-binding domain, between the metal-binding domain and the peptide linker, which connects it and the DNA-binding region of the molecule, and, in form I, between the DNA- and metal-binding domains. Molecular dynamics calculations were carried out based on the NOESY results and an adjustable square pyramidyl ligand geometry around Co(III) composed of nitrogen atoms of the primary and secondary amine groups, pyridine (N5), and amide and imidazole (N1) of the hydroxyhistidine residue. In form I, the bithiazole group folds back across the square pyramid forming a compact structure. Although this conformational feature was not observed in form II, the peptide linker between the metal- and DNA-binding domains in both species shows extensive folding based on a large number of intramolecular interactions.