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.