Type 2 periplasmic binding fold superfamily; This evolutionary model and hierarchy represent the ligand-binding domains found in solute binding proteins that serve as initial receptors in the transport, signal transduction and channel gating. The PBP2 proteins share the same architecture as periplasmic binding proteins type 1 (PBP1), but have a different topology. They are typically comprised of two globular subdomains connected by a flexible hinge and bind their ligand in the cleft between these domains in a manner resembling a Venus flytrap. The origin of PBP module can be traced across the distant phyla, including eukaryotes, archebacteria, and prokaryotes. The majority of PBP2 proteins are involved in the uptake of a variety of soluble substrates such as phosphate, sulfate, polysaccharides, lysine/arginine/ornithine, and histidine. After binding their specific ligand with high affinity, they can interact 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 energized by ATP hydrolysis. Besides transport proteins, the family includes ionotropic glutamate receptors and unorthodox sensor proteins involved in signal transduction. The substrate binding domain of the LysR transcriptional regulators and the oligopeptide-like transport systems also contain the type 2 periplasmic binding fold and thus they are significantly homologous to that of the PBP2; however, these two families are grouped into a separate hierarchy of the PBP2 superfamily due to the large number of protein sequences.

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gi 161077734 220 VDFLvaQMLRERLNFTMLLQQPEKKYFGERSANGSYNGAIGSIIKDGLDICLTGFFVkDYLVQQYMDFTVAVYDD 294
Cdd:cd13717   30 IDLI--EEISEILNFDYEIVEPEDGKFGTMDENGEWNGLIGDLVRKEADIALAALSV-MAEREEVVDFTVPYYDL 101

The ligand-binding domain of putative ionotropic glutamate receptors, a member of the type 2 periplasmic binding fold protein superfamily; This group contains glutamate receptor domain GluR. These domains are found in the GluR proteins that have been shown to function as L-glutamate activated potassium channels, also known ionotropic glutamate receptors or iGluRs. In addition to two ligand binding core domains, iGluRs typically have a channel-like domain inserted in the middle of the GluR-like domain. Animal iGluRs mediate the ion flux in the synapses of the CNS and can be subdivided into several classes depending on the neurotransmitter specificity and ion conductance properties. Their plant homologs have been shown to function in light signal transduction and calcium homeostasis. The GluR proteins belong to the PBPII 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.

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                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 161077734 220 VDFLvaQMLRERLNFTMLLQQPEKKYFGERSANGSYNGAIGSIIKDGLDICLTGFFVkDYLVQQYMDFTVAVYDD 294
Cdd:cd13717   30 IDLI--EEISEILNFDYEIVEPEDGKFGTMDENGEWNGLIGDLVRKEADIALAALSV-MAEREEVVDFTVPYYDL 101

The ligand-binding domain of putative ionotropic glutamate receptors, a member of the type 2 periplasmic binding fold protein superfamily; This group contains glutamate receptor domain GluR. These domains are found in the GluR proteins that have been shown to function as L-glutamate activated potassium channels, also known ionotropic glutamate receptors or iGluRs. In addition to two ligand binding core domains, iGluRs typically have a channel-like domain inserted in the middle of the GluR-like domain. Animal iGluRs mediate the ion flux in the synapses of the CNS and can be subdivided into several classes depending on the neurotransmitter specificity and ion conductance properties. Their plant homologs have been shown to function in light signal transduction and calcium homeostasis. The GluR proteins belong to the PBPII 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.

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                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 161077734 220 VDFLvaQMLRERLNFTMLLQQPEKKYFGERSANGSYNGAIGSIIKDGLDICLTGFFVkDYLVQQYMDFTVAVYDD 294
Cdd:cd13717   30 IDLI--EEISEILNFDYEIVEPEDGKFGTMDENGEWNGLIGDLVRKEADIALAALSV-MAEREEVVDFTVPYYDL 101