Thompson Aiysha, Kanamarlapudi Venkateswarlu
Institute of Life Science 1, College of Medicine, Swansea University, Singleton Park, Swansea, SA2 8PP, UK.
Sci Rep. 2014 Dec 15;4:7410. doi: 10.1038/srep07410.
The hGLP-1R is a target for the treatment of type 2 diabetes and belongs to the class B family of GPCRs. Like other class B GPCRs, the GLP-1R contains an N-terminal signal peptide (SP) and undergoes N-linked glycosylation, which are important for its trafficking and maturation. This study analysed the role of the SP, the hydrophobic region after the SP (HRASP), glycosylation and the conserved residues within the N-terminus in GLP-1R trafficking. HGLP-1R targeted to the cell surface showed no SP, and the SP deleted mutant, but not the mutants defective in SP cleavage, showed cell surface expression, demonstrating the importance of SP cleavage for hGLP-1R cell surface expression. The N-terminal deletions of hGLP-1R revealed that the HRASP, not the SP, is essential for cell surface expression of GLP-1R. Further, inhibition of hGLP-1R glycosylation prevented cell surface expression of the receptor. Mutation of Trp(39), Tyr(69) and Tyr(88), which are required for agonist binding, in the GLP-1R abolished cell surface expression of the receptor independent of the SP cleavage or N-linked glycosylation. In conclusion, the N-terminus of hGLP-1R regulates receptor trafficking and maturation. Therefore this study provides insight into the role of hGLP-1R N-terminus on the receptor cell surface expression.
人胰高血糖素样肽-1受体（hGLP-1R）是2型糖尿病的治疗靶点，属于G蛋白偶联受体（GPCR）的B类家族。与其他B类GPCR一样，GLP-1R含有一个N端信号肽（SP）并进行N-糖基化，这对其转运和成熟很重要。本研究分析了SP、SP后的疏水区域（HRASP）、糖基化以及N端保守残基在GLP-1R转运中的作用。靶向细胞表面的hGLP-1R没有SP，且SP缺失突变体而非SP切割缺陷的突变体显示出细胞表面表达，这证明了SP切割对hGLP-1R细胞表面表达的重要性。hGLP-1R的N端缺失表明，对于GLP-1R的细胞表面表达，HRASP而非SP是必需的。此外，抑制hGLP-1R糖基化会阻止该受体的细胞表面表达。GLP-1R中激动剂结合所需的色氨酸（Trp(39)）、酪氨酸（Tyr(69)）和酪氨酸（Tyr(88)）的突变消除了受体的细胞表面表达，且与SP切割或N-糖基化无关。总之，hGLP-1R的N端调节受体的转运和成熟。因此，本研究深入了解了hGLP-1R N端在受体细胞表面表达中的作用。
