title: Outer-sphere effects on reduction potentials of copper sites in proteins: the curious case of high potential type 2 C112D/M121E Pseudomonas aeruginosa azurin.
abstract: Redox and spectroscopic (electronic absorption, multifrequency electron paramagnetic resonance (EPR), and X-ray absorption) properties together with X-ray crystal structures are reported for the type 2 Cu(II) C112D/M121E variant of Pseudomonas aeruginosa azurin. The results suggest that Cu(II) is constrained from interaction with the proximal glutamate; this structural frustration implies a "rack" mechanism for the 290 mV (vs NHE) reduction potential measured at neutral pH. At high pH (∼9), hydrogen bonding in the outer coordination sphere is perturbed to allow axial glutamate ligation to Cu(II), with a decrease in potential to 119 mV. These results highlight the role played by outer-sphere interactions, and the structural constraints they impose, in determining the redox behavior of transition metal protein cofactors.
authors.affiliation: Beckman Institute, California Institute of Technology, Pasadena, California 91125, USA. kml04747@caltech.edu
authors.forename: Kyle M
authors.initials: KM
authors.lastname: Lancaster
authors.forename: Stephen
authors.initials: S
authors.lastname: Sproules
authors.forename: Joshua H
authors.initials: JH
authors.lastname: Palmer
authors.forename: John H
authors.initials: JH
authors.lastname: Richards
authors.forename: Harry B
authors.initials: HB
authors.lastname: Gray
mesh_terms: D001400:Azurin / Q000737:chemistry / Q000378:metabolism*; D003300:Copper / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D004591:Electrophoresis, Polyacrylamide Gel; D006860:Hydrogen Bonding; D010084:Oxidation-Reduction; D011550:Pseudomonas aeruginosa / Q000378:metabolism*; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D001400:Azurin; D003300:Copper