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Figure 1
(a) Reaction catalyzed by NTR. Reducing equivalents are transferred from NADPH to FAD bound to NTR. From FAD they are transferred to a disulfide bond in the NADPH domain of NTR and further to a disulfide in the Trx substrate. In order to catalyze the entire reaction, NTR needs to swap between two conformations: the flavin-oxidizing (FO) and flavin-reducing (FR) conformations. The electron transfer linked to each conformation is framed. (b) A schematic view of the FO and FR conformations as proposed by Waksman et al. (1994BB45). The two subunits in each NTR dimer are shown in blue and green, respectively. The darker coloured ovals symbolize the FAD domains, while the lighter coloured ovals show the NADPH domains. Disulfide and thiols are indicated as S-S and S-H, respectively. The black lines connecting the two domains symbolize the antiparallel β-sheets around which a 66° rotation occurs to bring NTR from the FO to the FR conformation. Thereby, the nicotine amide ring is positioned in proximity to the flavin isoalloxazine-ring system and the dithiols are brought to the surface of the protein where they can reduce Trx (shown in yellow). (c) The NTR reaction scheme modified to take the observation of differences in inter-domain interactions and lack of space for NADPH binding in the HvNTR2 crystal structure into account. Hydrogen bonds are shown by dotted lines. Trx interaction is required for breakage of inter-domain contacts in the FO conformation and domain reorientation, and NADPH/NADP+ is assumed not to bind during domain reorientation.

Journal logoBIOLOGICAL
ISSN: 1399-0047
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