ELECTROSTATIC DISTANCE GEOMETRY IN A K+ CHANNEL VESTIBULE

Many voltage-gated K+ channels carry in the external vestibule a recep tor for charybdotoxin, a peptide channel blocker. We use point mutagen esis of both charybdotoxin and a Shaker K+ channel to isolate the elec trostatic interaction energy between chosen pairs of residues, one on the channel and one on bound toxin. The results allow estimates of phy sical distances between such residue pairs and, in combination with th e known structure of charybdotoxin, localize specific channel residues in three-dimensional space.