Disease-Associated Mutations Prevent GPR56-Collagen III Interaction

GPR56 is a member of the adhesion G protein-coupled receptor (GPCR) family. Mutations in GPR56 cause a devastating human brain malformation called bilateral frontoparietal polymicrogyria (BFPP). Using the N-terminal fragment of GPR56 (GPR56N) as a probe, we have recently demonstrated that collagen III is the ligand of GPR56 in the developing brain. In this report, we discover a new functional domain in GPR56N, the ligand binding domain. This domain contains four disease-associated mutations and two N-glycosylation sites. Our study reveals that although glycosylation is not required for ligand binding, each of the four disease-associated mutations completely abolish the ligand binding ability of GPR56. Our data indicates that these four single missense mutations cause BFPP mostly by abolishing the ability of GPR56 to bind to its ligand, collagen III, in addition to affecting GPR56 protein surface expression as previously shown.GPR56是黏附型G蛋白偶联受体（adhesion G protein-coupled receptor, GPCR）家族的一员。GPR56的突变会引发一种致死性人类脑部畸形疾病——双侧额顶叶多小脑回（bilateral frontoparietal polymicrogyria, BFPP）。本研究以GPR56的N端片段（GPR56N）作为探针，近期证实III型胶原是发育中脑内GPR56的配体。本报告中，研究团队在GPR56N中发现了一个全新的功能结构域：配体结合域。该结构域包含4个与疾病相关的突变位点以及2个N-糖基化位点。研究结果显示，尽管糖基化修饰对GPR56的配体结合活性并非必需，但上述4个疾病相关突变均可完全消除其配体结合能力。本研究数据表明，这4个单氨基酸错义突变引发BFPP的主要致病机制，除如既往研究所证实的影响GPR56蛋白表面表达外，还在于其阻断了GPR56与其配体III型胶原的结合能力。