Intimations of K+ channel structure from a complete functional map of the molecular surface of charybdotoxin.

The external vestibules of many K+ channels carry a high-affinity receptor for charybdotoxin, a peptide of known structure. Point mutations of a recombinant toxin identified the residues directly involved in the interaction with a Ca(2+)-activated K+ channel. The interaction surface is formed from 8 of the 37 residues and covers about 25% of the peptide's molecular surface. The shape of the toxin permits a deduced picture of the complementary receptor site in the external vestibule of the K+ channel.