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Cytochrome ba3

Cytochrome ba3 from Thermus thermophilus belongs to the large family of structurally related heme-copper oxidases. It accepts electrons from cytochrome c552 at the P-side of the membrane and uses them to reduce oxygen to water. The oxygen catalysis is also coupled with proton pumping across the membrane but with lower than other heme-copper oxidases efficiency of only 0.5 protons per electron.

Like the canonical cytochrome oxidases cytochrome ba3 has 4 redox centers: electron-accepting CuA, low-spin heme b, high-spin heme a3, and CuB. Heme a3 and CuB form a binuclear center responsible for oxygen catalysis.

Structure of cytochrome ba3

Oxygen catalysis and proton pumping across the membrane require existence of proton conductive channels. Three of such channels were identified from the atomic crystal structure of cytochrome ba3. Two of these channels are reminiscent of the previously identified D- and K-pathways of cytochrome aa3, but the principal amino acid residues are not conserved between cytochromes aa3 and ba3. For instance, the highly conserved Glu-278 in the D-pathway of cytochrome aa3 is exchanged to Ile-235. Notably, similar to other heme-copper oxidases cytochrome ba3 has a tyrosine at the active site that is covalently linked to a histidine ligand of CuB.

Redox centers of cytochromes aa3 and ba3


References:
· Siletsky SA, Belevich I, Jasaitis A, Konstantinov AA, Wikström M, Soulimane T, Verkhovsky MI. Time-resolved single-turnover of ba(3) oxidase from Thermus thermophilus. // Biochim Biophys Acta. 2007 Dec;1767(12):1383-92.


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