PROSITE documentation PDOC60023
Omega-agatoxin type II and III signature


The spider venoms often contain many active peptides such as neurotoxins, lectins, inhibitors to enzyme, etc. These peptides are very important for spider's hunting and defending. During the long history of spider evolution, the peptides evolved into different structures and functions. Spider venoms possess a diverse array of peptide toxins composed of high number of cysteine residues varying from 6 to 14 [1]. Several peptide toxins, collectively referred to as omega-toxins, block with differential selectivity the different types of voltage-gated Ca2+ channels.

Omega-agatoxins from Agelenopsis aperta are small disulfide rich polypeptides which are grouped in different classes according to their pharmacological properties against N, L and P/Q calcium currents. Some omega-agatoxins are very specific such as type I, II and IV omega-agatoxins, which respectively block L, N and P currents. Type III omega-agatoxins are less selective and block both N and L currents with the same potency. Type II and type III omega-agatoxins have clear similarity regarding the location of cysteine residues which have a C-x(6)-C-x(6,8)-C-x-C-C-x(5)-C arrangement [2,3].

The following spider toxins contain the same cysteine arrangement:

  • Agelenopsis aperta (funnel-web spider) omega-agatoxin (omega-Aga)-IIA, -IIIA, -IIIB, -IIIC and -IIID.
  • Phoneutria nigriventer (brazilian armed spider) omega-phonetoxin (omega- Ptx)-IIA and PNTx22C5 [4].
  • Phoneutria reidyi (Brazilian Amazonian armed spider) neurotoxin PRTx18C2.
  • Ancylometes sp. (South American fishing spider) neurotoxin ANC32C7.

The pattern we have developed for this cysteine arrangement covers the last four cysteines.


Type I and IV omega-agatoxins are unrelated to type II and III omega- agatoxins. They have different cysteine arrangements (respectively C-x(6)-C- x-C-x(6)-C-x-C-x(11)-C-x-C-x(7)-C-x(5)-C and C-x(7)-C-x(6)-C-C-x(4)-C-x(6)-C- x-C) [2,3].

Expert(s) to contact by email:

Ramakumar S.

Last update:

September 2005 / First entry.


Technical section

PROSITE method (with tools and information) covered by this documentation:

OMEGA_AGA_II_III, PS60023; Omega-agatoxin type II and III signature  (PATTERN)


1AuthorsRajendra W. Armugam A. Jeyaseelan K.
TitleToxins in anti-nociception and anti-inflammation.
SourceToxicon 44:1-17(2004).
PubMed ID15225557

2AuthorsEscoubas P. Diochot S. Corzo G.
TitleStructure and pharmacology of spider venom neurotoxins.
SourceBiochimie 82:893-907(2000).
PubMed ID11086219

3AuthorsRash L.D. Hodgson W.C.
TitlePharmacology and biochemistry of spider venoms.
SourceToxicon 40:225-254(2002).
PubMed ID11711120

4AuthorsCassola A.C. Jaffe H. Fales H.M. Castro Afeche S. Magnoli F. Cipolla-Neto J.
Titleomega-phonetoxin-IIA: a calcium channel blocker from the spider phoneutria nigriventer.
SourcePflugers Arch. 436:545-552(1998).
PubMed ID9683727

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