8.B.11 The Sea Anemone Peptide Toxin Class 3 (APETx) Family

APETx2 inhibits several ASIC3-containing channels at concentrations from 63 nM to 2 microM. Its mode of action is unknown. Nevertheless, APETx2 structure is related to other sea anemone peptides, which act as gating modifiers on Nav and Kv channels (Diochot et al., 2007). Norton (2009) summarizes the various known Sea anemone ion channel blockers and modulators, as well as potent cytolysins.

Potently blocks the H(+)- gated sodium channel ASIC3 (ACCN3). The blockade is rapid and reversible. Does not block isoform ASIC1a and isoform ASIC1b of ASIC1 (ACCN2), or ASIC2 (ACCN1). It also inhibits heteromeric ASIC2b-ASIC3 channel, while it has less affinity for ASIC1b-ASIC3, ASIC1a-ASIC3, and no effect on the ASIC2a-ASIC3 channels.

APETx2 is homologous to APETx1 toxin, a specific peptide of the human ether-a-go-go-related K⁺ channels and to neurotoxin BcIV (P84919) of Bunodosoma caissarum which induces paralysis in crabs, and the antihypertensive peptides blood depressing substances BdsI and BdsII.