title: Role of the N-terminus of subunit III in proton uptake in cytochrome c oxidase of Rhodobacter sphaeroides.
abstract: The catalytic core of cytochrome c oxidase consists of three subunits that are conserved across species. The N-terminus of subunit III contains three histidine residues (3, 7, and 10) that are surface-exposed, have physiologically relevant pKa values, and are in close proximity of the mouth of the D-channel in subunit I. A triple-histidine mutation (to glutamine) was created in Rhodobacter sphaeroides. The mutant enzyme retains 60% of wild-type activity. Absorbance during steady-state turnover indicates that electrons accumulate at heme a in the mutant, accompanied by accumulation of the oxoferryl intermediate. When reconstituted into liposomes, the mutant enzyme pumps protons with an efficiency that is half that of the wild type. Finally, the mutant exhibits a lower cytochrome c peroxidation rate. Our results indicate that the mutation lowers activity indirectly by slowing the uptake of protons through the D-channel and that the three histidine residues stabilize the interactions between subunit I and subunit III.
authors.affiliation: Department of Biochemistry and Molecular Biology, Boonshoft School of Medicine, Wright State University , Dayton, Ohio 45435, United States.
authors.forename: Khadijeh S
authors.initials: KS
authors.lastname: Alnajjar
authors.forename: Jonathan
authors.initials: J
authors.lastname: Hosler
authors.forename: Lawrence
authors.initials: L
authors.lastname: Prochaska
mesh_terms: D019943:Amino Acid Substitution; D020134:Catalytic Domain / Q000235:genetics; D003576:Electron Transport Complex IV / Q000737:chemistry*; D005973:Glutamine / Q000235:genetics; D006639:Histidine / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D021122:Protein Subunits / Q000737:chemistry*; D017494:Proton Pumps / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000201:enzymology
chemical_list: D021122:Protein Subunits; D017494:Proton Pumps; D005973:Glutamine; D006639:Histidine; D003576:Electron Transport Complex IV