ω-Grammotoxin SIA is a 36 amino acid residue protein toxin from spider venom that inhibits P, Q, and N-type
voltage-gated calcium channels in neurons. It binds to the channels with high affinity (if closed). It also binds to
potassium channels but with lower affinity than to the
calcium channels. The toxin binding site has high affinity when channels are in closed states and low affinity when channels are activated. (4) == Mode of action ==