Structure of the binuclear heme iron-copper site in the quinol-oxidizing cytochrome aa3 from Bacillus subtilis (original) (raw)

1994, Biochimica et Biophysica Acta (BBA) - Bioenergetics

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 Cu A center typical of the cytochrome c oxidases is lacking from cytochrome aa3-600. The presence of only one copper, viz. Cu B 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 Biophys. J. 34, 465-468). Heme Fea3 has a proximal histidine nitrogen ligand 2.10 + 0.02 ,~ from the iron, and a distal S or C1 ligand at 2.36 ___ 0.03 A. The latter is also a ligand of Cu B (2.21 + 0.02 ,~), and apparently forms a bridge between the two metals which are 3.70 + 0.06 A apart. Cu B has two more close-lying ligands at 1.95 + 0.02 ,~, which are likely histidine nitrogens. The similarity between EXAFS of Cu B and type 1 'blue' copper is contrasted to EPR and optical spectroscopic properties of Cu B, and the nature of the bridging ligand is discussed.