Module 3: Figure P2X receptor structure
Structural organization of the human P2X1 receptor.
The P2X receptor has two transmembrane domains with the N- and C-terminal regions extending into the cytoplasm. There is an extensive extracellular loop that contains the ATP-binding site that has both hydrophobic residues (Phe-185 and Phe-291) that bind to the adenine ring and charged residues (Lys-68, Arg-292 and Lys-309) that interact with the phosphates. The structural integrity of the extracellular domain is maintained by a number of disulphide bonds. The functional P2X channel is a trimeric structure. The N-terminal region contains a threonine that is phosphorylated by protein kinase C (PKC), which may enhance channel activity by reducing the rate of desensitization. This regulation through PKC may play an important role in nociception (Module 10: Figure nociception).