Electrostatic distance geometry in a K+ channel vestibule.

Many voltage-gated K+ channels carry in the external vestibule a receptor for charybdotoxin, a peptide channel blocker. We use point mutagenesis of both charybdotoxin and a Shaker K+ channel to isolate the electrostatic interaction energy between chosen pairs of residues, one on the channel and one on bound toxin. The results allow estimates of physical distances between such residue pairs and, in combination with the known structure of charybdotoxin, localize specific channel residues in three-dimensional space.