8.B.12 The Spider Toxin (STx2) Family
Phoneutria nigriventer toxins, PnTx2-5 and PnTx2-6, markedly delay the fast inactivation kinetics of neuronal-type sodium channels, but they have differences in their interactions with the channel (Matavel et al., 2009). PnTx2-6 has an affinity 6 times higher than that of PnTx2-5, and its effects are not reversible within 10-15 min of washing. PnTx2-6 partially (59%) competes with the scorpion alpha-toxin AaHII, but not with the scorpion beta-toxin CssIV, thus suggesting a mode of action similar to that of site 3 toxins. However, PnTx2-6 is not removed by strong depolarizing pulses, as in the known site 3 toxins. Matavel et al., 2009 also established that the cysteines in these poorly helical toxins are in their oxidized form.
Tx2-5 of Phoneutria nigriventer (P29424)
Omega-ctenitoxin-Pn4a, CnTx-Pn4a; neurotoxin Tx3-6; α1-β toxin of 90 aas
Tx3.6 of Phoneutria nigriventer
Hainantoxin XV-2, HnTx-XV-2 of 117 aas.
HnTx-XV-2 of Haplopelma hainanum
Cystine knot toxin of 114 aas
Cystine knot toxin of Dolomedes mizhoanus
Omega-ctenitoxin-Pn4a of 90 aas and 1 TMS. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. It is a potent blocker of high voltage-activated calcium channels, acting mainly on P/Q-type (Cav2.1/CACNA1A) calcium channels and with a minor effect on L- (Cav1/CACNA1) and N-type (Cav2.2/CACNA1B) calcium channels (Vieira et al. 2005). It blocks glutamate release in synaptic transmission mediated by calcium channels (Vieira et al. 2003). The toxin also inhibits the KCl-induced increase of intrasynaptosomal free calcium (Souza et al. 2008).
Toxin of Phoneutria nigriventer (Brazilian armed spider)