Mechanism of allosteric regulation of β-adrenergic receptor by cholesterol.

There is evidence that lipids can be allosteric regulators of membrane protein structure and activation. However, there are no data showing how exactly the regulation emerges from specific lipid-protein interactions. Here we show in atomistic detail how the human β-adrenergic receptor (βAR) - a prototypical G protein-coupled receptor - is modulated by cholesterol in an allosteric fashion. Extensive atomistic simulations show that cholesterol regulates βAR by limiting its conformational variability. The mechanism of action is based on the binding of cholesterol at specific high-affinity sites located near the transmembrane helices 5-7 of the receptor. The alternative mechanism, where the βAR conformation would be modulated by membrane-mediated interactions, plays only a minor role. Cholesterol analogues also bind to cholesterol binding sites and impede the structural flexibility of βAR, however cholesterol generates the strongest effect. The results highlight the capacity of lipids to regulate the conformation of membrane receptors through specific interactions.