APETx1 is a peptide toxin from the venom of the sea anemone Anthopleura elegantissima.
[1][2] Furthermore, the secondary structure of the peptide consists of four-stranded anti-parallel beta-sheets.
[3] Moreover, APETx1 has 54% sequence homology with BDS1, which is also produced by sea anemones and targets voltage-gated potassium channels as well.
[2][4] On the S3b helix, the amino acids on positions 514 and 518 are on the same side and are both extracellularly exposed, allowing them to bind with APETx1.
[1] APETx1 blocks voltage-gated sodium channels by binding to neurotoxin site 1, similar to tetrodotoxin.