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  • 标题:Structural dynamics and energetics underlying allosteric inactivation of the cannabinoid receptor CB1
  • 本地全文:下载
  • 作者:Jonathan F. Fay ; David L. Farrens
  • 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:2015
  • 卷号:112
  • 期号:27
  • 页码:8469-8474
  • DOI:10.1073/pnas.1500895112
  • 语种:English
  • 出版社:The National Academy of Sciences of the United States of America
  • 摘要:SignificanceG protein-coupled receptors (GPCRs) are a major pharmaceutical target. Traditionally, they were thought to lead a binary existence, adopting either an off (inactive) or on (active) state. However, recent evidence suggests GPCRs can adopt multiple conformations and these might explain biased signaling--the phenomena where different drugs binding to the same orthosteric site on the receptor can cause activation of different signaling pathways, such as {beta}-arrestin signaling. We show a previously unidentified structure is induced in the marijuana receptor CB1 by an unusual allosteric ligand that blocks G-protein signaling but increases agonist binding and elicits biased signaling. We propose that a common structural state may exist for {beta}-arrestin biased signaling, one that can also be attained by allosteric ligand binding. G protein-coupled receptors (GPCRs) are surprisingly flexible molecules that can do much more than simply turn on G proteins. Some even exhibit biased signaling, wherein the same receptor preferentially activates different G-protein or arrestin signaling pathways depending on the type of ligand bound. Why this behavior occurs is still unclear, but it can happen with both traditional ligands and ligands that bind allosterically outside the orthosteric receptor binding pocket. Here, we looked for structural mechanisms underlying these phenomena in the marijuana receptor CB1. Our work focused on the allosteric ligand Org 27569, which has an unusual effect on CB1--it simultaneously increases agonist binding, decreases G-protein activation, and induces biased signaling. Using classical pharmacological binding studies, we find that Org 27569 binds to a unique allosteric site on CB1 and show that it can act alone (without need for agonist cobinding). Through mutagenesis studies, we find that the ability of Org 27569 to bind is related to how much receptor is in an active conformation that can couple with G protein. Using these data, we estimated the energy differences between the inactive and active states. Finally, site-directed fluorescence labeling studies show the CB1 structure stabilized by Org 27569 is different and unique from that stabilized by antagonist or agonist. Specifically, transmembrane helix 6 (TM6) movements associated with G-protein activation are blocked, but at the same time, helix 8/TM7 movements are enhanced, suggesting a possible mechanism for the ability of Org 27569 to induce biased signaling.
  • 关键词:GPCR ; CB1 ; protein dynamics ; allosteric ; biased signaling
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