Proton translocating nicotinamide nucleotide transhydrogenase from E. coli. Mechanism of action deduced from its structural and catalytic properties11This review is dedicated to the memory of Professor Lars Ernster.

Abstract

Transhydrogenase couples the stereospecific and reversible transfer of hydride equivalents from NADH to NADP(+) to the translocation of proton across the inner membrane in mitochondria and the cytoplasmic membrane in bacteria. Like all transhydrogenases, the Escherichia coli enzyme is composed of three domains. Domains I and III protrude from the membrane and contain the binding site for NAD(H) and NADP(H), respectively. Domain II spans the membrane and constitutes at least partly the proton translocating pathway. Three-dimensional models of the hydrophilic domains I and III deduced from crystallographic and NMR data and a new topology of domain II are presented. The new information obtained from the structures and the numerous mutation studies strengthen the proposition of a binding change mechanism, as a way to couple the reduction of NADP(+) by NADH to proton translocation and occurring mainly at the level of the NADP(H) binding site.

Fast Hydride Transfer in Proton-translocating Transhydrogenase Revealed in a Rapid Mixing Continuous Flow Device

“…Thus, as the dIII in one trimer enters the open state to permit product release and substrate binding, the other enters the occluded state to permit hydride transfer; the two trimers run 180 o out of phase. In general, a mechanism of coupling involving changes in NADP(H) binding is also favored by other authors (17)(18)(19).…”

Nicotinamide Nucleotide Transhydrogenase (Nnt) Links the Substrate Requirement in Brain Mitochondria for Hydrogen Peroxide Removal to the Thioredoxin/Peroxiredoxin (Trx/Prx) System

“…Approximately 45% of NADPH in the mitochondria is produced by nicotinamide nucleotide transhydrogenase (Nnt) and the remainder comes from NADP ϩ -isocitrate dehydrogenase 2 or mitochondrial NAD(P)-malic enzyme (16,17). What separates Nnt from the other mechanisms of NADPH production is it utilizes the proton gradient generated through the citric acid cycle and the electron transport chain to convert NADP ϩ into NADPH (18,19). The role of Nnt in mitochondrial redox regulation has been demonstrated previously in studies, which showed that Nnt inhibition decreased GSH redox status and increased sensitivity to oxidative stress; however, its role in modulating the Trx/ Prx system in brain mitochondria remains unknown (16, 20 -22).…”

Proteomic and Transcriptomic Elucidation of the Mutant Ralstonia eutropha G + 1 with Regard to Glucose Utilization

“…Transhydrogenase from E. coli is composed of an ␣ subunit (PntA, 54 kDa) and a ␤ subunit (PntB, 48 kDa), building an active form of ␣ 2 ␤ 2 . As is the case for all proton-translocating transhydrogenases, the enzyme is composed of three domains: the hydrophilic domain I (for E. coli, ␣1 to ␣402) containing the NAD(H) binding site, a hydrophobic domain II (for E. coli, ␣-403 to ␤260) harboring the membrane spanning ␣-helices, and a hydrophilic domain III (for E. coli, ␤261 to ␤462) containing the NADP(H) binding site (6).…”