Chemical synthesis and characterization of ShK toxin: a potent potassium channel inhibitor from a sea anemone.

ShK-toxin, a 35 residue peptide isolated from the sea anemone Stichodactyla helianthus, was synthesized using an Fmoc strategy and successfully folded to the biologically active form containing three intramolecular disulfide bonds. The ability of synthetic ShK toxin to inhibit specific [125I]-dendrotoxin I binding to rat brain membranes slightly exceeded (was more potent than) that of the natural ShK toxin sample, but was comparable with previously reported data for ShK toxin. The peptide toxin inhibited [125I]-charybdotoxin binding to Jurkat T lymphocytes with an IC50 value of 32 pM. In addition, Jurkat T lymphocytes Kv1.3 potassium channels were inhibited with an IC50 value of 133 pM. Owing to their unique structure and high affinity for at least some potassium channels, ShK toxin and related sea anemone potassium channel toxins may become useful molecular probes for investigating potassium channels.