Division of labor in transhydrogenase by alternating proton translocation and hydride transfer

Abstract

Dueling dimers serve dual purposes Both bacteria and mitochrondria produce NADPH for amino acid biosynthesis and to remove reactive oxygen species. The enzyme that makes NADPH must translocate a proton across the membrane and transfer a hydride from NADH to NADP + —processes that happen some 40 Å apart. To understand this complex geometry, Leung et al. solved the structures of the entire transhydrogenase enzyme and the membrane domain from the bacterium Thermus thermophilus (see the Perspective by Krengel and Törnroth-Horsefield). The entire enzyme exists as a dimer, with the two membrane domains in alternate orientations. One of the membrane domains interacts with the membrane component for proton translocation, whereas the other domain exchanges hydride with NAD(H) in another large soluble domain. Science , this issue p. 178 ; see also p. 125