The Cu-A domain of Thermus thermophilus ba(3)-type cytochrome c oxidase at1.6 angstrom resolution

The structure of the Cu-A-containing, extracellular domain of Thermus therm ophilus ba(3)-type cytochrome c oxidase has been determined to 1.6 Angstrom resolution using multiple X-ray wavelength anomalous dispersion (MAD). The Cu2S2 cluster forms a planar rhombus with a copper-copper distance of 2.51 +/- 0.03 Angstrom, X-ray absorption fine-structure (EXAFS) studies show th at this distance is unchanged by crystallization. The Cu, center is asymmet rical; one copper is tetrahedrally coordinated to two bridging cysteine thi olates, one histidine nitrogen and one methionine sulfur, while the other i s trigonally coordinated by the two cysteine thiolates and a histidine nitr ogen. Combined sequence-structure alignment of amino acid sequences reveals conserved interactions between cytochrome c oxidase subunits I and II.