| Primary Identifier | IPR044527 | Type | Domain |
| Short Name | NrtA/CpmA_ABC-bd_dom |
| description | This entry includes a domain found in nitrate (Nrt) and bicarbonate (Cmp) receptors. This domain is found in eubacterial periplasmic-binding proteins that serve as initial receptors in the ABC transport of bicarbonate, nitrate, taurine, or a wide range of aliphatic sulfonates []. After binding its ligand with high affinity, it interacts with a cognate membrane transport complex comprised of two integral membrane domains and two cytoplasmically located ATPase domains. This interaction triggers the ligand translocation across the cytoplasmic membrane energised by ATP hydrolysis. These binding proteins belong to the PBP2 superfamily of periplasmic-binding proteins that differ in size and ligand specificity, but have similar tertiary structures consisting of two globular subdomains connected by a flexible hinge. They have been shown to bind their ligand in the cleft between these domains in a manner resembling a Venus flytrap [].In cyanobacteria, nitrate transport takes place through NRT system, a multicomponent ABC transporter. NRT consists of 4 proteins: a periplasmic substrate-binding protein (NrtA) involved in the specific and high affinity binding of nitrate and nitrite. NrtB is a hydrophobic protein with structural similarities to integral membrane subunits of ABC transporters []. It is thought to form a pore across the membrane to allow the translocation of nitrate and nitrite. Finally, NrtC and NrtD are proposed to form a heterodimer associated to the inner side of the cytoplasmic membrane, and to be responsible of energising the transport system via ATP hydrolysis. In NrtC the binding site for ATP in found at the N-terminal [].The cmpA, cmpB, cmpC, and cmpD genes are strongly similar to the genes encoding the nitrate/nitrite transporter, nrtA, nrtB, nrtC, and nrtD, respectively. NrtB and CmpB are hydrophobic proteins with structural similarities to the integral membrane components of ABC transporters. CmpC and CmpD are ATP-binding cassette proteins strongly similar to NrtC and NrtD, respectively. CmpA is a cytoplasmic membrane protein, which is 46.5% identical to NrtA that functions as the membrane-anchored substrate (nitrate and nitrite)-binding protein []. The similarity of CmpA to NrtA and its involvement in HCO(3)(-) uptake suggest that CmpA is the substrate-binding protein of the HCO(3)(-) transporter []. |
