Figure 1.

Active site structure of the DMSO reductase subfamilies members. The DMSO reductase family has been divided in three subfamilies according to the different elements coordinating the Mo atom at the active site, including: the dissimilatory nitrate reductase (Nap) and formate dehydrogenase (Fdh) (subfamily I) in which the active site is coordinated by a Cys (Nap) or a Se‐Cys (Fdh); the respiratory nitrate reductase (Nar) (subfamily II) where Mo is coordinated by one or two oxygen atoms from an aspartate residue, and the DMSO reductase and trimethylmanine N‐oxide (TMAO) reductase (subfamily III) with the side chain of a Ser residue in the coordinating position. Note that the scheme is not exhaustive and some members are not represented, as for example arsenite oxidase (Aio), which has also been assigned as belonging to the DMSO reductase family of Mo‐containing enzymes, but with some unusual properties when compared to the other members, namely the lack of an amino acid side chain as a metal ligand. The resolution of the crystal structures available for the Nap, Fdh, and Nar proteins (subfamilies I and II) as well as the 6th Mo ligand are also represented in the tables.