Structure of the binuclear heme iron-copper site in the quinol-oxidizing cytochrome aa3 from Bacillus subtilis.
Cytochrome aa3-600 is a terminal quinol oxidase of Bacillus subtilis, belonging to the large family of structurally and functionally related respiratory enzymes to which the mitochondrial cytochrome c oxidase also belongs. However, the CuA center typical of the cytochrome c oxidases is lacking from cytochrome aa3-600. The presence of only one copper, viz. CuB of the binuclear heme iron-copper site, makes cytochrome aa3-600 especially suitable for XAS analysis of this structure. Cu and Fe XAS data for fully oxidized cytochrome aa3-600 indicate a structure for the binuclear site similar to that previously reported for mitochondrial cytochrome c oxidase (see Powers et al. (1981) Biophys. J. 34, 465-468). Heme Fea3 has a proximal histidine nitrogen ligand 2.10 +/- 0.02 A from the iron, and a distal S or Cl ligand at 2.36 +/- 0.03 A. The latter is also a ligand of CuB (2.21 +/- 0.02 A), and apparently forms a bridge between the two metals which are 3.70 +/- 0.06 A apart. CuB has two more close-lying ligands at 1.95 +/- 0.02 A, which are likely histidine nitrogens. The similarity between EXAFS of CuB and type 1 'blue' copper is contrasted to EPR and optical spectroscopic properties of CuB, and the nature of the bridging ligand is discussed.
Powers
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National Center for the Design of Molecular Function, Utah State University, Logan 84322.
Lauraeus
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M
Reddy
K S
KS
Chance
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B
Wikström
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M
D001412:Bacillus subtilis / Q000201:enzymology*; D002712:Chlorides / Q000378:metabolism; D003300:Copper / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D003576:Electron Transport Complex IV / Q000737:chemistry*; D006418:Heme / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D010088:Oxidoreductases / Q000737:chemistry*
D002712:Chlorides; D006418:Heme; D003300:Copper; D007501:Iron; D010088:Oxidoreductases; C020094:duroquinol oxidase; D003576:Electron Transport Complex IV