期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2010
卷号：107
期号：9
页码：4454-4458
DOI：10.1073/pnas.0914261107
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：G protein-coupled receptors (GPCRs) play central roles in almost all physiological functions; mutations in GPCRs are responsible for more than 30 disorders. There is a great deal of information about GPCR structure but little information that directly relates structure to protein trafficking or to activation. The gonadotropin releasing hormone receptor, because of its small size among GPCRs, is amenable to preparation of mutants and was used in this study to establish the relation among a salt bridge, protein trafficking, and receptor activation. This bridge, between residues E90 [located in transmembrane segment (TM) 2] and K121 (TM3), is associated with correct trafficking to the plasma membrane. Agonists, but not antagonists, interact with residue K121, and destabilize the TM2-TM3 association of the receptor in the plasma membrane. The hGnRHR mutant E90K has a broken salt bridge, which also destabilizes the TM2-TM3 association and is typically retained in the endoplasmic reticulum. We show that this mutant, if rescued to the plasma membrane by either of two different means, has constitutive activity and shows modified ligand specificity, revealing a role for the salt bridge in receptor activation, ligand specificity, trafficking, and structure. The data indicate that destabilizing the TM2-TM3 relation for receptor activation, while requiring an intact salt bridge for correct trafficking, provides a mechanism that protects the cell from plasma membrane expression of constitutive activity.
