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.


 

References:

and Shiomi K. (2009). Novel peptide toxins recently isolated from sea anemones. Toxicon. 54(8):1112-8.
Chagot, B., P. Escoubas, S. Diochat, C. Bernard, M. Lazdunski, and H. Darbon.  (2005).  Solution structure of APETx2, a specific peptide inhibitor of ASIC3 proton-gated channels.  Protein Sci. 14(8): 2003-2010. 
Diochot, S., M. Salinas, A. Baron, P. Escoubas, and M. Lazdunski. (2007). Peptides inhibitors of acid-sensing ion channels. Toxicon 49: 271-284.
Norton, R.S. (2009). Structures of sea anemone toxins. Toxicon 54: 1075-1088.
Examples:

TC#NameOrganismal TypeExample
8.B.11.1.1APETx1 toxin (a human ether-a-go-go-related gene potassium channel toxin) (Shiomi, 2009)

Sea anemones

APETx1 toxin of Anthopleura elegantissima (P61541)

 
8.B.11.1.2APETx2 toxin (42 aas) (an acid-sensing sodium channel toxin) (Shiomi, 2009).

Sea anemones

APETx2 toxin of Anthopleura elegantissma (P61542)

 
8.B.11.1.3The hypertensive BdsI (3D structure known) (a Kv3 potassium channel toxins) (Shiomi, 2009).

Sea anemones

BdsI of Anemonia sulcata (P11494)

 
8.B.11.1.4The BcIV toxin (a sodium channel toxin) (Shiomi, 2009).

Sea anemones

BcIV toxin of Bunodosoma caissarum (P84919)