Heme-copper oxidases with modified D- and K-pathways are yet efficient proton pumps

The cytochrome aa(3)-type quinol oxidase from the archaeon Acidianus ambiva lens and the ba(3)-type cytochrome c oxidase from Thermus thermophilus are divergent members of the heme-copper oxidase superfamily of enzymes. In par ticular they lack most of the key residues involved in the proposed proton transfer pathways, The pumping capability of the A. ambivalens,ls enzyme wa s investigated and found to occur with the same efficiency as the canonical enzymes. This is the first demonstration of pumping of 1 H+/electron in a heme-copper oxidase that lacks most residues of the K- and D-channels, Also , the structure of the ba(3) oxidase from T. thermophilus was simulated by mutating Phe274 to threonine and Glu278 to isoleucine in the D-pathway of t he Paracoccus denitrificans cytochrome c oxidase. This modification resulte d in full efficiency of proton translocation albeit with a substantially lo wered turnover. Together, these findings show that multiple structural solu tions for efficient proton conduction arose during evolution of the respira tory oxidases, and that very few residues remain invariant among these enzy mes to function in a common proton-pumping mechanism. (C) 2001 Federation o f European Biochemical Societies. Published by Elsevier Science B.V. All ri ghts reserved.