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)
Spiderine-1a of 166 aas and 1 TMS. It has antimicrobial, insecticidal, cytolytic and cytotoxic activity, and is active against E. coli, E. faecalis, B. subtilis, A. globiformis, P. aeruginosa and S. aureus in submicromolar or low micromolar ranges. It also lyses human erythrocytes and kills HeLA and A549 cells (Vassilevski et al. 2013).
Spiderine of Oxyopes takobius (Lynx spider) (Oxyopes foliiformis)