Interaction of charybdotoxin with permeant ions inside the pore of a K+ channel

Neuron. 1992 Aug;9(2):307-13. doi: 10.1016/0896-6273(92)90169-e.


Charybdotoxin (CTX) blocks high conductance Ca(2+)-activated K+ channels by binding to a receptor site in the externally facing "mouth." Toxin bound to the channel can be destabilized from its site by K+ entering the channel from the opposite, internal, solution. By analyzing point mutants of CTX expressed in E. coli, assayed with single Ca(2+)-activated K+ channels reconstituted into planar lipid bilayers, we show that a single positively charged residue of the peptide, Lys-27, wholly mediates this interaction of K+ with CTX. If position 27 carries a positively charged residue, internal K+ accelerates the dissociation rate of CTX in a voltage-dependent manner; however, if a neutral Asn or Gln is substituted at this position, the dissociation rate is completely insensitive to either internal K+ or applied voltage. Position 27 is unique in this respect; charge-neutral substitutions made at other positions fail to eliminate the K+ destabilization phenomenon. The results argue that CTX bound to the channel positions Lys-27 physically close to a K(+)-specific binding site on the external end of the conduction pathway and that a K+ ion occupying this site destabilizes CTX via direct electrostatic repulsion with the epsilon-amino group of Lys-27.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcium / pharmacology*
  • Charybdotoxin
  • Electric Conductivity
  • Electrochemistry
  • Escherichia coli / metabolism
  • Kinetics
  • Lipid Bilayers / metabolism
  • Lysine / chemistry
  • Mutagenesis
  • Potassium / metabolism
  • Potassium / pharmacology
  • Potassium Channels / metabolism*
  • Rats
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Scorpion Venoms / chemistry
  • Scorpion Venoms / genetics
  • Scorpion Venoms / metabolism*
  • Structure-Activity Relationship


  • Lipid Bilayers
  • Potassium Channels
  • Recombinant Proteins
  • Scorpion Venoms
  • Charybdotoxin
  • Lysine
  • Potassium
  • Calcium