Fig. 3: Mutational analysis of the StnC subunit.
From: Molecular architecture and electron transfer pathway of the Stn family transhydrogenase
a Surface representation of StnC with six [4Fe4S]-clusters and one [2Fe2S]-cluster, along with the FAD-NADPH binding site shown. The oxidation of NADPH triggers the electron flow from FAD in StnC to the FMN in StnB. b, c Zoom-ins of the FAD binding site and C7 cluster encased around cryo-EM density. d NADPH binds at the pocket carved by two Rossmann folds in the StnC subunit. e Comparison of the FAD binding site in StnC and NfnB subunits. Residue R201 in NfnB forms a hydrogen bond with N5 of FAD. The corresponding R239 in StnC also participates in hydrogen bonding but not with the N5 of FAD. f, g Transhydrogenase activity assays performed for different complex variants probing the roles of R239, K170, and C114. Fdox-dependent NADPH:NAD+ oxidoreductase activity of StnABC-His in comparison to variants StnC_R239A, StnC_R239K, StnC_K170R, StnC_K170A, StnC_K170C and StnC_C114A. Activities are the mean ± s.e.m. of three independent biological replicates, measured in triplicates (n = 3). Activities are given in U/mg. One Unit is defined as the transfer of 2 µmol electrons/min.
