Structure of zinc-independent sorbitol dehydrogenase from Rhodobacter sphaeroides at 2.4 A resolution.

Recombinant sorbitol dehydrogenase (SDH) from Rhodobacter sphaeroides has been crystallized in the absence of the cofactor NAD(H) and its structure determined to 2.4 A resolution using molecular replacement (refined R and R free factors of 18.8 and 23.8%, respectively). As expected from the sequence and shown by the conserved fold, SDH can be assigned to the short-chain dehydrogenase/reductase protein family. The cofactor NAD and the substrate sorbitol have been modelled into the structure and the active-site architecture, which displays the highly conserved catalytic tetrad of Asn-Ser-Tyr-Lys residues, is discussed in relation to the enzyme mechanism. This is the first structure of a bacterial SDH belonging to the SDR family.