Family 2.A.6 - The Resistance-Nodulation-Cell Division Family       

Family ID: 52617

Characterized members of the RND superfamily all probably catalyze substrate efflux via an H+ antiport mechanism. These proteins are found ubiquitously in bacteria, archaea and eukaryotes. Most of the RND superfamily transport systems consist of large polypeptide chains (700-1300 amino acyl residues long). These proteins possess a single transmembrane spanner (TMS) at their N-termini followed by a large extracytoplasmic domain, then six additional TMSs, a second large extracytoplasmic domain, and five final C-terminal TMSs. In the case of one system (NolGHI) the system may consist of three distinct polypeptide chains, and most of the SecDF homologues consist of two polypeptide chains. Most others probably consist of a single polypeptide chain. The first halves of RND family proteins are homologous to the second halves, and the proteins therefore probably arose as a result of an intragenic tandem duplication event that occurred in the primordial system prior to divergence of the family members. One protein homologue from Methanococcus jannaschii is of half size and has no internal duplication. It can be postulated to function as a homo- or heterodimer in the membrane. The same is true of the eukaryotic RND family homologues that do not appear to function in transport. Some of the eukaryotic proteins have hydrophilic C-terminal domains.