Two Classes of Cholesterol Binding Sites for the ?2AR Revealed by*Thermostability and NMR.
Two Classes of Cholesterol Binding Sites for the ?2AR Revealed by*Thermostability and NMR.
Biophys J. 2014 Nov 18;107(10):2305-12
Authors: Gater DL, Saurel O, Iordanov I, Liu W, Cherezov V, Milon A
Abstract
Cholesterol binding to G protein-coupled receptors (GPCRs) and modulation of their activities in membranes is a fundamental issue for understanding their function. Despite the identification of cholesterol binding sites in high-resolution x-ray structures of the ?2 adrenergic receptor (?2AR) and other GPCRs, the binding affinity of cholesterol for this receptor and exchange rates between the free and bound cholesterol remain unknown. In this study we report the existence of two classes of cholesterol binding sites in ?2AR. By analyzing the ?2AR unfolding temperature in lipidic cubic phase (LCP) as a function of cholesterol concentration we observed high-affinity cooperative binding of cholesterol with sub-nM affinity constant. In contrast, saturation transfer difference (STD) NMR experiments revealed the existence of a second class of cholesterol binding sites, in fast exchange on the STD NMR timescale. Titration of the STD signal as a function of cholesterol concentration provided a lower limit of 100*mM for their dissociation constant. However, these binding sites are specific for both cholesterol and ?2AR, as shown with control experiments using ergosterol and a control membrane protein (KpOmpA). We postulate that this specificity is mediated by the high-affinity bound cholesterol molecules and propose the formation of transient cholesterol clusters around the*high-affinity binding sites.
PMID: 25418299 [PubMed - in process]
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