Torres G E, Egan T M, Voigt M M
Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, St. Louis, Missouri 63104, USA.
J Biol Chem. 1999 Mar 5;274(10):6653-9. doi: 10.1074/jbc.274.10.6653.
P2X receptors are a distinct family of ligand-gated ion channels activated by extracellular ATP. Each of the seven identified subunit proteins (P2X1 through P2X7) has been reported to form functional homo-oligomeric channels when expressed in heterologous systems. Functional studies of native receptors, together with patterns of subunit gene expression, suggest that hetero-oligomeric assembly among members of this family may also occur. This prediction is supported by reports describing hetero-oligomeric assembly for three different recombinant subunit combinations. In this report, we systematically examined the ability of all members of the P2X receptor family to interact using a co-immunoprecipitation assay. The seven P2X receptor subunits were differentially epitope-tagged and expressed in various combinations in human embryonic kidney 293 cells. It was found that six of the seven subunits formed homo-oligomeric complexes, the exception being P2X6. When co-assembly between pairs of subunits was examined, all were able to form hetero-oligomeric assemblies with the exception of P2X7. Whereas P2X1, P2X2, P2X5, and P2X6 were able to assemble with most subunits, P2X3 and P2X4 presented a more restricted pattern of co-association. These results suggest that hetero-oligomeric assembly might underlie functional discrepancies observed between P2X responses seen in the native and recombinant settings, while providing for an increased diversity of signaling by ATP.
P2X受体是一类独特的配体门控离子通道，可被细胞外ATP激活。据报道，已鉴定出的七种亚基蛋白（P2X1至P2X7）中的每一种在异源系统中表达时都会形成功能性同聚体通道。对天然受体的功能研究以及亚基基因表达模式表明，该家族成员之间也可能发生异聚体组装。这一预测得到了描述三种不同重组亚基组合的异聚体组装的报道的支持。在本报告中，我们使用共免疫沉淀试验系统地研究了P2X受体家族所有成员之间相互作用的能力。七个P2X受体亚基用不同的表位标签标记，并以各种组合在人胚肾293细胞中表达。发现七个亚基中有六个形成了同聚体复合物，例外的是P2X6。当检查亚基对之间的共组装时，除了P2X7之外，所有亚基都能够形成异聚体组装。虽然P2X1、P2X2、P2X5和P2X6能够与大多数亚基组装，但P2X3和P2X4的共缔合模式更为受限。这些结果表明，异聚体组装可能是天然和重组环境中P2X反应之间观察到的功能差异的基础，同时增加了ATP信号传导的多样性。
