Structure and mechanism of proton-translocating transhydrogenase.

Recent developments have led to advances in our understanding of the structure and mechanism of action of proton-translocating (or AB) transhydrogenase. There is (a) a high-resolution crystal structure, and an NMR structure, of the NADP(H)-binding component (dIII), (b) a homology-based model of the NAD(H)-binding component (dI) and (c) an emerging consensus on the position of the transmembrane helices (in dII). The crystal structure of dIII, in particular, provides new insights into the mechanism by which the energy released in proton translocation across the membrane is coupled to changes in the binding affinities of NADP(+) and NADPH that drive the chemical reaction.