Chiral Specificity of Cholesterol Orientation Within Cholesterol Binding Sites in Inwardly Rectifying K⁺ Channels

Cholesterol is an integral component of cellular membranes and has been shown to be an important functional regulator for many different ion channels, including inwardly rectifying potassium (Kir) channels. Consequently, understanding the molecular mechanisms underlying this regulation represents a critical field of study. Broadly speaking, cholesterol can mediate ion channel function either directly by binding to specific sites or indirectly by altering surrounding membrane properties. Owing to the similar effects of cholesterol and its chiral isomers (epicholesterol and ent-cholesterol) on membrane properties, comparative analysis of these sterols can be an effective tool for discriminating between these direct and indirect effects. Indeed, this strategy was used to demonstrate the direct effect of cholesterol on Kir channel function. However, while this approach can discriminate between direct and indirect effects, it does not account for the promiscuity of cholesterol binding sites, which can potentially accommodate cholesterol or its chiral isomers. In this chapter, we use docking analyses to explore the idea that the specificity of cholesterol's effect on Kir channels is dependent on the specific orientation of cholesterol within its putative binding pocket which its chiral isomers cannot replicate, even when bound themselves.