Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan.
Integrative Physiology, Department of Physiology, Graduate School of Medicine, Osaka University, 2-2 Yamada-oka, Suita, Osaka, 565-0871, Japan.
Sci Rep. 2017 Mar 23;7:45208. doi: 10.1038/srep45208.
P2X receptors are trimeric ATP-gated cation channels involved in diverse physiological processes, ranging from muscle contraction to nociception. Despite the recent structure determination of the ATP-bound P2X receptors, the molecular mechanism of the nucleotide base specificity has remained elusive. Here, we present the crystal structure of zebrafish P2X4 in complex with a weak affinity agonist, CTP, together with structure-based electrophysiological and spectroscopic analyses. The CTP-bound structure revealed a hydrogen bond, between the cytosine base and the side chain of the basic residue in the agonist binding site, which mediates the weak but significant affinity for CTP. The cytosine base is further recognized by two main chain atoms, as in the ATP-bound structure, but their bond lengths seem to be extended in the CTP-bound structure, also possibly contributing to the weaker affinity for CTP over ATP. This work provides the structural insights for the nucleotide base specificity of P2X receptors.
P2X 受体是三聚体 ATP 门控阳离子通道，参与多种生理过程，从肌肉收缩到痛觉。尽管最近已经确定了 ATP 结合的 P2X 受体的结构，但核苷酸碱基特异性的分子机制仍然难以捉摸。在这里，我们展示了与弱亲和力激动剂 CTP 结合的斑马鱼 P2X4 的晶体结构，以及基于结构的电生理和光谱分析。CTP 结合结构揭示了胞嘧啶碱基与激动剂结合位点中碱性残基侧链之间的氢键，该氢键介导了对 CTP 的弱但显著的亲和力。胞嘧啶碱基进一步被两个主链原子识别，就像在 ATP 结合结构中一样，但它们的键长在 CTP 结合结构中似乎被延长，这也可能导致 CTP 对 P2X 受体的亲和力比 ATP 弱。这项工作为 P2X 受体的核苷酸碱基特异性提供了结构见解。
