This superfamily represents the death-like domain (DLD) of Spt6 (Suppressor of Ty 6, originally discovered in Saccharomyces cerevisiae), a gene that influences general transcription through manipulation of chromatin structure at upstream promoter elements [].This DLD domain maintains the characteristic overall topology of death domains, as it consists of a six-helix bundle with three stacked antiparallel helices and an additional helix inserted between the final two helices of the bundle. The Spt6 DLD prominent location and the observation that it displays the most highly conserved region of the Spt6 surface suggest that it mediates important intermolecular interactions [, ].
D-lactate dehydrogenases catalyse the reversible oxidation of D-lactate to pyruvate. This entry represents the NADH-independent D-lactate dehydrogenases found in many bacterial species. These are membrane-associated respiratory enzymes which contain an FAD cofactor and transfer electrons derived from susbstrate oxidation to the electron transfer chain. The energy derived from this reaction can be coupled either to ATP generation or the active uptake of solutes. The Escherichia coli enzyme () is a peripheral membrane enzyme located on the cyctoplasmic side of the inner membrane, which passes the electrons derived from substrate oxidation to the quinone component of the electron transfer chain []. It is composed of three domains: an FAD-binding domain, a cap domain and a membrane-binding domain. The FAD-binding domain has a similar fold to that of other FAD-linked enzymes, being composed of two α-β subdomains, with the FAD cofactor being accommodated between them. The cap domain forms an α-β-alpha sandwich, while the membrane-binding region is composed of four alpha helices which show an excess of basic residues over acidic ones. The enzyme is thought to be anchored to the membrane by electrostatic interactions between these basic reidues and the negatively charged phospholipid head groups of the membrane. The active site of the enzyme is not known, but is thought to be located close to the FAD-binding site, at the interface of all three domains.Proteins in this entry also include quinone-dependent D-lactate dehydrogenase Dld from Corynebacterium glutamicum. It is essential for growth with D-lactate as sole carbon source [].
