Molecular dynamics simulation of the follicle-stimulating hormone receptor. Understanding the conformational dynamics of receptor variants at positions N680 and D408 from in silico analysis

Follicle-stimulating hormone receptor (FSHR) is a G-protein coupled receptor (GPCR) and a prototype of the glycoprotein hormone receptors subfamily of GPCRs. Structural data of the FSHR ectodomain in complex with follicle-stimulating hormone suggests a “pull and lift” activation mechanism that triggers a conformational change on the seven α-helix transmembrane domain (TMD). To analyze the conformational changes of the FSHR TMD resulting from sequence variants associated with reproductive impairment in humans, we set up a computational approach combining helix modeling and molecular simulation methods to generate conformational ensembles of the receptor at room (300 K) and physiological (310 K) temperatures. We examined the receptor dynamics in an explicit membrane environment of polyunsaturated phospholipids and solvent water molecules. The analysis of the conformational dynamics of the functional (N680 and S680) and dysfunctional (mutations at D408) variants of the FSHR allowed us to validate the FSHR-TMD model. Functional variants display a concerted motion of flexible intracellular regions at TMD helices 5 and 6. Disruption of side chain interactions and conformational dynamics were detected upon mutation at D408 when replaced with alanine, arginine, or tyrosine. Dynamical network analysis confirmed that TMD helices 2 and 5 may share communication pathways in the functional FSHR variants, whereas no connectivity was detected in the dysfunctional mutants, indicating that the global dynamics of the FSHR was sensitive to mutations at amino acid residue 408, a key position apparently linked to misfolding and variable cell surface plasma membrane expression of FSHRs with distinct mutations at this position.

促卵泡激素受体（Follicle-stimulating hormone receptor, FSHR）属于G蛋白偶联受体（G-protein coupled receptor, GPCR）家族，为糖蛋白激素受体亚家族的原型成员。与促卵泡激素结合的FSHR胞外域结构数据表明，其存在‘牵拉-提升’激活机制，该机制可触发七α螺旋跨膜结构域（TMD）发生构象变化。为解析人类生殖功能受损相关序列变异所引发的FSHR TMD构象变化，本研究搭建了一套融合螺旋建模与分子模拟的计算方法，用于生成该受体在室温（300 K）与生理温度（310 K）下的构象系综。我们在由多不饱和磷脂构成的显式膜环境与溶剂水分子体系中，对受体的动态行为进行了表征。通过对FSHR功能变体（N680与S680）以及功能异常变体（D408位点突变）的构象动态进行分析，我们验证了FSHR-TMD模型。功能变体可观察到TMD第5、6螺旋处的柔性胞内区域发生协同运动。当D408位点被丙氨酸、精氨酸或酪氨酸替换时，可检测到侧链相互作用与构象动态遭到破坏。动态网络分析证实，在功能FSHR变体中，TMD第2、5螺旋可能共享通信通路；而功能异常突变体中未检测到此类连通性。这表明FSHR的全局动态对氨基酸残基408处的突变极为敏感——该位点显然与该位置存在不同突变的FSHR的错误折叠以及可变的细胞表面血浆膜表达密切相关。