Disease-associated mutations affect GPR56 protein trafficking and cell surface expression
Disease-associated mutations affect GPR56 protein trafficking and cell surface expression
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DOI：
10.1093/hmg/ddm144
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发表时间：
2007-08-15
影响因子：
3.5
通讯作者：
Piao, Xianhua
中科院分区：
文献类型：
--
作者：
Jin, Zhaohui;Tietjen, Ian;Piao, Xianhua
双侧额顶叶多微回畸形（BFPP）是一种先天性脑畸形，导致皮质表面不规则，其中正常的回旋回被许多（多）和明显较小的（微）回所取代。患有BFPP的个体患有癫痫、智力迟钝、语言障碍和运动发育迟缓。编码G蛋白偶联受体56（GPR 56）的基因突变导致BFPP;然而，目前尚不清楚这些突变如何影响GPR 56的功能。在这里，我们研究野生型和突变体GPR 56的生化特性和蛋白质运输。我们证明，GPR 56蛋白经历了两个主要的修改，GPS结构域介导的蛋白质切割和N-糖基化，并且N-末端片段可以从细胞表面释放。与野生型蛋白质相反，N-末端结构域尖端的疾病相关GPR 56错义突变（R38 Q、R38 W、Y88 C和C91 S）产生具有减少的细胞内运输和差的细胞表面表达的蛋白质，而GPS结构域中的两个突变（C346 S和W349 S）产生具有显著受损的切割的蛋白质，其不能运输超出内质网。细胞运输障碍被药理学伴侣部分消除，可以部分挽救突变体GPR 56细胞表面表达。这些数据表明，GPR 56中的一些BFPP相关突变损害了突变蛋白向质膜的运输，从而为BFPP相关突变如何影响GPR 56功能提供了见解。
Bilateral frontoparietal polymicrogyria (BFPP) is a congenital brain malformation resulting in irregularities on the surface of the cortex, where normally convoluted gyri are replaced by numerous (poly) and noticeably smaller (micro) gyri. Individuals with BFPP suffer from epilepsy, mental retardation, language impairment and motor developmental delay. Mutations in the gene-encoding G protein-coupled receptor 56 (GPR56) cause BFPP; however, it remains unclear how these mutations affect GPR56 function. Here, we examine the biochemical properties and protein trafficking of wild-type and mutant GPR56. We demonstrate that GPR56 protein undergoes two major modifications, GPS domain-mediated protein cleavage and N-glycosylation, and that the N-terminal fragment can be released from the cell surface. In contrast to the wild-type protein, disease-associated GPR56 missense mutations in the tip of the N-terminal domain (R38Q, R38W, Y88C and C91S) produce proteins with reduced intracellular trafficking and poor cell surface expression, whereas the two mutations in the GPS domain (C346S and W349S) produce proteins with dramatically impaired cleavage that fail to traffic beyond the endoplasmic reticulum. Cell-trafficking impairments are abrogated in part by pharmacological chaperones that can partially rescue mutant GPR56 cell surface expression. These data demonstrate that some BFPP-associated mutations in GPR56 impair trafficking of the mutant protein to the plasma membrane, thus providing insights into how BFPP-associated mutations affect GPR56 function.