Liu Yu, Zhang Lei, Shao Xiao-Xia, Hu Meng-Jun, Liu Ya-Li, Xu Zeng-Guang, Guo Zhan-Yun
Research Center for Translational Medicine, College of Life Sciences and Technology, Tongji University, Shanghai, China.
Research Center for Translational Medicine, College of Life Sciences and Technology, Tongji University, Shanghai, China.
Arch Biochem Biophys. 2016 Aug 15;604:113-20. doi: 10.1016/j.abb.2016.06.013. Epub 2016 Jun 25.
Relaxin-3 is an insulin/relaxin superfamily neuropeptide involved in the regulation of food intake and stress response via activation of its cognate receptor RXFP3, an A-class G protein-coupled receptor (GPCR). In recent studies, a highly conserved ExxxD motif essential for binding of relaxin-3 has been identified at extracellular end of the second transmembrane domain (TMD2) of RXFP3. For most of the A-class GPCRs, a highly conserved negatively charged Asp residue (Asp(2.50) using Ballesteros-Weinstein numbering and Asp128 in human RXFP3) is present at the middle of TMD2. To elucidate function of the conserved transmembrane Asp128, in the present work we replaced it with other residues and the resultant RXFP3 mutants all retained quite high ligand-binding potency, but their activation and agonist-induced internalization were abolished or drastically decreased. Thus, the negatively charged transmembrane Asp128 controlled transduction of agonist-binding information from the extracellular region to the intracellular region through maintaining RXFP3 in a metastable state for efficient conformational change induced by binding of an agonist.
松弛素-3是一种胰岛素/松弛素超家族神经肽，通过激活其同源受体RXFP3（一种A类G蛋白偶联受体（GPCR））参与食物摄入和应激反应的调节。在最近的研究中，已在RXFP3的第二个跨膜结构域（TMD2）的细胞外末端鉴定出对松弛素-3结合至关重要的高度保守的ExxxD基序。对于大多数A类GPCR，在TMD2的中部存在一个高度保守的带负电荷的天冬氨酸残基（使用Ballesteros-Weinstein编号为Asp(2.50)，在人RXFP3中为Asp128）。为了阐明保守的跨膜天冬氨酸128的功能，在本研究中我们将其替换为其他残基，所得的RXFP3突变体均保留了相当高的配体结合能力，但其激活和激动剂诱导的内化被消除或大幅降低。因此，带负电荷的跨膜天冬氨酸128通过将RXFP3维持在亚稳态以实现由激动剂结合诱导的有效构象变化，从而控制激动剂结合信息从细胞外区域到细胞内区域的转导。
