title: Catalytic reduction of dioxygen with modified Thermus thermophilus cytochrome c552.
abstract: Efficient catalysis of the oxygen reduction reaction (ORR) is of central importance to function in fuel cells. Metalloproteins, such as laccase (Cu) or cytochrome c oxidase (Cu/Fe-heme) carry out the 4H(+)/4e(-) reduction quite efficiently, but using large, complex protein frameworks. Smaller heme proteins also can carry out ORR, but less efficiently. To gain greater insight into features that promote efficient ORR, we expressed, characterized, and investigated the electrochemical behavior of six new mutants of cytochrome c552 from Thermus thermophilus: V49S/M69A, V49T/M69A, L29D/V49S/M69A, P27A/P28A/L29D/V49S/M69A, and P27A/P28A/L29D/V49T/M69A. Mutation to V49 causes only minor shifts to Fe(III/II) reduction potentials (E°'), but introduction of Ser provides a hydrogen bond donor that slightly enhances oxygen reduction activity. Mutation of L29 to D induces small shifts in heme optical spectra, but not to E°' (within experimental error). Replacement of P27 and P28 with A in both positions induces a -50 mV shift in E°', again with small changes to the optical spectra. Both the optical spectra and reduction potentials have signatures consistent with peroxidase enzymes. The V49S and V49T mutations have the largest impact of ORR catalysis, suggesting that increased electron density at the Fe site does not improve O2 reduction chemistry.
authors.affiliation: Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Husband
authors.affiliation: Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Aaron
authors.affiliation: Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada.
authors.forename: Rajneesh K
authors.initials: RK
authors.lastname: Bains
authors.affiliation: Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Lewis
authors.affiliation: Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada. Electronic address: j.warren@sfu.ca.
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Warren
mesh_terms: D066241:Carbon-13 Magnetic Resonance Spectroscopy; D002384:Catalysis; D003574:Cytochrome c Group / Q000378:metabolism*; D010100:Oxygen / Q000737:chemistry*; D016963:Thermus thermophilus / Q000201:enzymology*
chemical_list: D003574:Cytochrome c Group; C022302:cytochrome C-552; D010100:Oxygen
keywords: Electrochemistry; Heme proteins; Oxygen reduction; Proton relay