Regulator of K+ conductance (RCK) domains form a conserved class of ligand-binding domains that control the activity of a variety of prokaryotic and eukaryotic K+ channels. Structural analysis of these domains by X-ray crystallography has provided insight toward mechanisms underlying ligand binding and channel gating, and thus the experimental strategies aimed at determining structures of liganded and unliganded forms of the domains may be useful in analysis of other ligand-binding domains. Here, we describe a basic strategy for crystallographic analysis of the RCK domain from the MthK channel, for determination of its Ca2+ -bound structure.
