Cholesterol is a major lipid constituent of the plasma membrane. Many ion channels are reported to be sensitive to cholesterol either by direct binding or via indirect effects, such as physical changes in membrane properties or alterations in protein trafficking to the cell surface, but mechanistic understanding of cholesterol’s action remains to be fully understood. One class of ion channels regulated by cholesterol are the G protein coupled inwardly rectifying potassium (GIRK) channels, which are involved in cell excitability and neurotransmission. The GIRK2 homotetramer and especially the GIRK1/2 heterotetramer are expressed in multiple brain regions, including those associated with reward, pain, and addiction. We performed whole-cell patch clamp recordings of GIRK1/2 overexpressed in HEK-293T cells and report that enrichment of the plasma membrane with cholesterol reduces GIRK1/2 activity. Molecular dynamics simulations were run to compare how cholesterol acts on the GIRK1/2 heterotetramer high-resolution structure and the GIRK2 homotetrameric structure, which was previously reported to be activated by cholesterol. Simulation data and corresponding mutagenesis studies indicate that cholesterol primarily acts to constrict or dilate the HBC gate of each ion channel, respectively. We additionally characterize the role of the GIRK2 M187 residue (L176 in GIRK1), which is critical for determining the cholesterol sensitivity of GIRK channels. Clarifying the structural mechanisms by which cholesterol differentially regulates GIRK2 and GIRK1/2 could lead to a better understanding of cholesterol effects in chronic pain and addiction.
Pentikis et al. (Sun,) studied this question.