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Rubrum transdehydrogenase NAD-binding and catalytic domains Transhydrogenases found in bacterial and inner mitochondrial membranes link NAD(P)(H)-dependent redox reactions to proton translocation. The energy of the proton electrochemical gradient (delta-p), generated by the respiratory electron transport chain, is consumed by transhydrogenase in NAD(P)+ reduction. Transhydrogenase is likely involved in the regulation of the citric acid cycle. Rubrum transhydrogenase has 3 components, dI, dII, and dIII. dII spans the membrane while dI and dIII protrude on the cytoplasmic/matrix side. DI contains 2 domains in Rossmann-like folds, linked by a long alpha helix, and contains a NAD binding site. Two dI polypeptides (represented in this sub-family) spontaneously form a heterotrimer with dIII in the absence of dII. In the heterotrimer, both dI chains may bind NAD, but only one is well-ordered. dIII also binds a well-ordered NADP, but in a different orientation than a classical Rossmann domain.
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Jiyao W et al.(2023). "The conserved domain database in 2023.",