Overview of structurally homologous flavoprotein oxidoreductases containing the low Mr thioredoxin reductase-like fold – A functionally diverse group

Thioredoxin reductase from Bacillus cereus exhibits distinct reduction and NADPH‐binding properties

“…The changes introduced to the sequence of B. cereus TrxR mutant , also depicted in Figure 2, include: (1) insertion of an extra linker between the FAD and NADPH-binding domains named "GAF", consisting of tree amino acids; glycine, alanine and phenylalanine (conserved in FNRs including B. cereus FNR2 and Bacillus subtilis FNR/YumC); (2) mutation of the redox-active cysteines to serines; (3) mutation of residue 320 (glutamate to serine), which is shown to form a hydrogen bond with the N5 atom on FAD in FNRs. In the latter, this residue is situated on the C-terminal loop, protruding over and stabilizing the FAD cofactor of the neighboring subunit, whereas in TrxRs, the Cterminal helix extends to the surface of the protein in the dimer interface, distant from the FAD cofactors [26,49,50].…”

“…A sequence alignment and phylogenetic tree of selected TrxRs and TrxR‐like FNRs can be seen in Figs 2 and 3 . The CXXC motif and the common sequence motifs HRRXXXR for the 2′phosphate group of NADPH and GXGXXA/G and GXGXXG for the pyrophosphate groups of NAD(P)H and FAD, respectively, are also highlighted [ 26 ] Three extra residues in one of the hinge regions are conserved among FNRs and absent in TrxRs. This extended linker is hypothesized to play a role in the rotation of the NADPH‐domain in FNRs and could be important for access and reduction of NrdI/Fld.…”

“…cereus FNR2 and Bacillus subtilis FNR/YumC); (b) mutation of the redox‐active cysteines to serines; and (c) mutation of residue 320 (glutamate to serine), which is shown to form a hydrogen bond with the N5 atom on FAD in FNRs. In the latter, this residue is situated on the C‐terminal loop, protruding over and stabilizing the FAD cofactor of the neighboring subunit, whereas in TrxRs, the C‐terminal helix extends to the surface of the protein in the dimer interface, distant from the FAD cofactors [ 26 , 49 , 50 ].…”

“…The TrxR-like FNRs constitute a large and diverse group of oxidoreductases, many of which have been discovered and characterized recently. These enzymes have evolved to perform a diverse set of biochemical reactions on different substrates [26]. The firmicute B. cereus encodes NrdI, two Flds, one TrxR, and three TrxR-like FNRs, FNR1−3.…”

Thiol Reductases in Deinococcus Bacteria and Roles in Stress Tolerance

“…Bacterial TrxRs, like those of archaea, fungi and plants, are composed of two subunits of 35 kDa, each possessing FAD-(flavin adenine dinucleotide) and NADPH-binding domains. These low-molecular-weight TrxRs are characterised by a specific fold found in several types of enzymes that catalyse diverse chemical reactions [50]. The electron transfer from NADPH via FAD to the active site disulfide, located in the NADPH-binding domain, leads to a large conformational change [51].…”