P2RX2

Official Full Name

purinergic receptor P2X 2

Organism

Homo sapiens

GeneID

22953

Background

The product of this gene belongs to the family of purinoceptors for ATP. This receptor functions as a ligand-gated ion channel. Binding to ATP mediates synaptic transmission between neurons and from neurons to smooth muscle. Multiple transcript variants encoding distinct isoforms have been identified for this gene. [provided by RefSeq, Aug 2013]

Synonyms

P2X2; DFNA41;

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Detailed Information

Overview

P2X receptor is a ligand-gated ion channel. The P2X receptor belongs to the P2 receptor family, and its ligand is ATP. P2X receptor channels open when extracellular ATP is bound, allowing the passage of cations (Na⁺, Ca²⁺, etc.). Seven mammalian P2X (P2X1-7) receptors have been cloned and their pharmacological properties have been elucidated. Natural P2X receptors can be assembled into homomorphic or heteromorphic polymers to form functional ion channels.

Figure 1. The 3D stracture of P2RX2.

Structure

P2X receptors are structurally similar to amiloride inward rectifier potassium channels and skin-sensitive sodium channel, both having two transmembrane domain structure. They often connect two wear extracellular loop of membrane structure domains with residues including 2-6 glycine (Gly) residues and 10 conserved cysteine (Cys) residues, forming a stable disulfide bond spatial structure. Transmembrane domain plays a role in channel function and has been shown to be important in determining the timing of P2X receptor responses. Studies have shown that the second transmembrane structure domain (TM2) has a β-folding plate and is related to the formation of channel holes, but the detailed structure of the pore area and the role of TM2 on channel holes need to be further studied.

Like other ion channels, the P2X receptor is oligomeric and consists of a minimum of 3 and a maximum of 6 subunits. There is evidence that both homopolymers and heteropolymers are expressed in vivo. When transfected into HEK293 cell line, or xenopus oocyte, the P2X receptor can also be assembled into a polysome with other LGICs, such as the a-subunit 1 of the neuronicotinoid cholinergic receptor. At present, the nucleotide binding site of P2X receptor is still unclear. It is speculated that Lys residue in the extracellular ring plays a nucleotide binding role, and data suggest that P2X receptor may have two ligand binding sites.

Functions

P2X receptor function can also be altered by extracellular ions. Protons, bivalent cations and monovalent ions all have effects on the potency and reaction degree of the agonist. In most cases, ions act on the receptor directly, but protons and cations can also bind to ATP, leading to different forms of ATP molecules. The proton can increase or decrease the potency of ATP. Divalent cations (such as Ca²⁺ and Mg²⁺) affect the binding of ATP to P2X receptors, but there must be a high concentration. For example, calcium can reduce the potency of ATP to P2RX2 and P2X in PC12 cells: when NaCI is replaced by sucrose or other Na-free and chlorine-free buffer, univalent cations and anions can increase the potency of agonist by 20-30 times.

Recombinant P2RX2 in xenopus oocyte showed that the P2X receptor-mediated response was enhanced by the application of enkephalin, substance P, calcitonin and other gene-related peptides and nerve growth factor (NGF). Whether these effects are mediated by allosteric, g-protein coupled receptors, and subsequent second messenger systems remains to be demonstrated. However, these results have led to an interest in the possibility that the function of the natural P2X receptor may be regulated by the g-protein-coupled receptor.

References:

Virgilio D, Chiozzi F, Ferrari O, et al. 2001,Nucleotide receptors: an emerging family of regulatory molecules in blood cells [J]. Blood, 97:587-600.
Cseri J, Szappanos H, Szigeti GP, et al. 2002, A purinergic signal transduction pathway in mammalian skeletal muscle cells in culture [J]. Plugers Arch, 443: 731-738.
Harden TK. Boyer JL, Nicholas RA. 1995, P2 purinergic receptor: subtype-associated signaling responses and structure [J]. Ann IRev Pharmacol Toxicol, 35:541-579.
Khakh BS. Burnstock G, Kennedy C, et al. 2001, Internationalunion of pharmacology. XXIV. Current status of the nomen clature and properties of P2X receptors and their subunits [J]. Phurmacol Rev, 53:107-118.
Lundy PM, Hamilton MG, Mi L, et al. 2002, Stimulation of Ca2+ influx through ATP receptors on rat brain synaptosomes: identification of functional P2X7 receptor subtypes [J]. Br J Pharmacol, 125. 1616-1624.
Frances MA. 2000. Ion channels and disease [M]. London UK: Academic Press, 405-407. MA.

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