title: Probing variable axial ligation in nickel superoxide dismutase utilizing metallopeptide-based models: insight into the superoxide disproportionation mechanism.
abstract: Nickel superoxide dismutase (NiSOD) is a bacterial metalloenzyme that possesses a mononuclear Ni-center and catalyzes the disproportionation of O2*- by cycling between NiII and NiIII oxidation states. Herein we present evidence from several SOD active metallopeptide maquettes ([Ni(SODM2H(1)X)]; SODM2H(1)X = H2N-XCDLPCG-COOH; X = H, D, or A) that the Ni-center of NiSOD most likely remains five-coordinate during SOD catalysis using thin-film voltammetry. N3- and CN- titration studies suggest that O2*- disproportionation by [Ni(SODM2H(1)X)] proceeds via an outersphere mechanism. Computationally derived values for the nuclear reorganization energy of the [NiII(SODM2)]/[NiIII(SODM2)] self-exchange reaction combined with the experimentally determined value for ko ( approximately 450 s-1) suggest that axial ligation enhances the O2*- disproportionation reaction in [Ni(SODM2)] (and NiSOD by analogy) by optimizing the NiII/NiIII redox couple such that it is close to the midpoint of the O2*- reduction and oxidation couples.
authors.affiliation: Department of Chemistry, University of Nevada, Reno, Reno, Nevada 89557, USA.
authors.forename: Kosh P
authors.initials: KP
authors.lastname: Neupane
authors.forename: Kristie
authors.initials: K
authors.lastname: Gearty
authors.forename: Ashish
authors.initials: A
authors.lastname: Francis
authors.forename: Jason
authors.initials: J
authors.lastname: Shearer
mesh_terms: D018360:Crystallography, X-Ray; D008958:Models, Molecular; D009532:Nickel / Q000378:metabolism*; D010084:Oxidation-Reduction; D010455:Peptides / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013482:Superoxide Dismutase / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism*
chemical_list: D010455:Peptides; D013481:Superoxides; D009532:Nickel; D013482:Superoxide Dismutase