Effects of Membrane Cholesterol on the Structure and Function of Selected Class A GPCRs─Challenges and Future...

Cholesterol can affect class A G protein-coupled receptors (GPCRs) function since it can modulate membrane properties, but can also bind to allosteric sites, with positions and numbers that can be general and conserved or can depend on the unique receptor and its functional state. The reliable identification and characterization of cholesterol-interaction sites, which can help toward the development of novel allosteric drugs, is challenging, but different biophysical methods, such as structural biology and molecular dynamics simulations, can be combined toward this aim. We reviewed results for 14 receptors selected based on phylogenetic relationships, functional relevance, and their established significance as therapeutic targets. The precise mechanistic interpretation of the effect of cholesterol at a molecular level is generally ambiguous for many class A GPCRs. Additionally, the experimentally observed effect of cholesterol on the function of a receptor often varies, likely due to variations in experimental systems, including cell types, lipid environments, protein constructs, or methodological differences. To elucidate the role of cholesterol in GPCR function, a robust methodological framework is required─one that integrates diverse biophysical techniques with carefully controlled experimental conditions, particularly regarding membrane composition and cellular context. Additionally, combining insights from both in vitro and in vivo studies is crucial for developing a comprehensive understanding of cholesterol's role in GPCR modulation.