Family C of G-protein coupled receptors and their close homologs, the type I periplasmic-binding proteins of ATP-binding cassette transporter-like systems
This CD includes members of the family C of G-protein coupled receptors and their close homologs, the type I periplasmic-binding proteins of ATP-binding cassette transporter-like systems. The family C GPCR includes glutamate/glycine-gated ion channels such as the NMDA receptor, G-protein-coupled receptors, metabotropic glutamate, GABA-B, calcium sensing, phermone receptors, and atrial natriuretic peptide-guanylate cyclase receptors. The glutamate receptors that form cation-selective ion channels, iGluR, can be classified into three different subgroups according to their binding-affinity for the agonists NMDA (N-methyl-D-asparate), AMPA (alpha-amino-3-dihydro-5-methyl-3-oxo-4-isoxazolepropionic acid), and kainate. L-glutamate is a major neurotransmitter in the brain of vertebrates and acts through either mGluRs or iGluRs. mGluRs subunits possess seven transmembrane segments and a large N-terminal extracellular domain. ABC-type leucine-isoleucine-valine-binding protein (LIVBP) is a bacterial periplasmic binding protein that has homology with the amino-terminal domain of the glutamate-receptor ion channels (iGluRs). The extracellular regions of iGluRs are made of two PBP-like domains in tandem, a LIVBP-like domain that constitutes the N terminus - which is included in this CD - followed by a domain related to lysine-arginine-ornithine-binding protein (LAOBP) that belongs to the type II periplasmic binding fold protein superfamily. The uncharacterized periplasmic components of various ABC-type transport systems are included in this group.