Aug 15, 1995

Structure of CuB in the binuclear heme-copper center of the cytochrome aa3-type quinol oxidase from Bacillus subtilis: an ENDOR and EXAFS study

Biochemistry
Y C FannMårten Wikström

Abstract

We have studied the structure of the CuB site in the binuclear heme-copper center of the fully oxidized form of the quinol-oxidizing cytochrome aa3-600 from Bacillus subtilis by EXAFS and ENDOR spectroscopy. This enzyme is member of the large superfamily of heme-copper respiratory oxidases, which catalyze the reduction of dioxygen to water and link it to translocation of protons across the bacterial or mitochondrial membrane. The EXAFS of the CuB site strongly suggests tetragonal coordination by two or three histidines with one or two O/N donor ligands. There are some indications that a Cl- ion might fractionally occupy substitution-labile sites, although the majority of enzyme molecules did not contain any heavy (second row) scatters, indicative of a Cl- (or S) bridge between the heme iron and CuB [cf. Powers, L., et al. (1994) Biochim. Biophys. Acta 1183, 504-512]. Proton ENDOR spectroscopy of the CuB site in 1H2O and 2H2O media showed evidence of an oxygenous copper ligand with an exchangeable proton. 14N ENDOR revealed three inequivalent nitrogenous ligands with hyperfine coupling constants consistent with histidines. Together, these results strongly suggest that the fully oxidized enzyme has a low-symmetry, tetragonal CuB ...Continue Reading

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Mentioned in this Paper

Cytochrome c Oxidase Subunit VIa
Histidine
Oxidase
Mitochondrial Membranes
Copper
Bacillus subtilis
Protein Conformation
Quinol oxidase
Natto Bacteria
Intracellular Translocation

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