Filling of a water-free void explains the allosteric regulation of the β1-adrenergic receptor by cholesterol

Abstract

Proteins often contain cavities, which are usually assumed to be water-filled. Recent high-pressure NMR results indicate that the preactive conformation of the {beta}1-adrenergic receptor ({beta}1AR) contains completely empty cavities (dry voids) of about [~]100 [A]3 volume, which disappear in the active conformation of the receptor. Here we have localized these cavities by X-ray crystallography on xenon-derivatized {beta}1AR crystals. One of the cavities coincides with the binding pocket of cholesterol. Solution NMR data show that addition of the soluble cholesterol analog cholesteryl hemisuccinate (CHS) impedes the formation of the active conformation of the receptor by blocking conserved GPCR microswitches. This wedge-like action explains the function of the cellularly highly abundant cholesterol as a negative allosteric modulator of {beta}1AR. The detailed understanding of GPCR regulation by cholesterol via filling of a dry void and the easy scouting for such voids by xenon may provide new routes for the development of allosteric drugs.