8.B.5 The Na+/K+/Ca2+ Channel Targeting Tarantula Huwentoxin (THT) Family
Protoxins inhibit voltage-gated calcium (Cav3.1/CACNA1G), potassium (Kv2.1/KCNB1) and sodium (Nav1.5) channels and shift the voltage-dependence of channel activation to more positive potentials. They potently inhibit all sodium channel subtypes tested (Nav1.2/SCN2A, Nav1.5/SCN5A, Nav1.7/SCN9A, and Nav1.8/SCN10A).
Protoxins 1 (35aas) and 2 (30aas) are peptide toxins from the venom of the tarantula, Thrixopelma pruriens, that conform to the inhibitory cystine knot motif and which modify activation kinetics of Nav and Cav, but not Kv, channels. ProTx-II inhibits current by shifting the voltage dependence of activation to more depolarized potentials (Smith et al., 2007).
Many plant and animal toxins cause aversive behaviors in animals due to their pungent or unpleasant taste or because they cause other unpleasant senstations like pain. Cromer and McIntyre (2007) have reviewed toxins that act at the TRPV1 ion channel expressed in primary sensory neurons. This channel is activated by multiple painful stimuli and is thought to be a key pain sensor and integrator. The painful peptide 'vanillotoxin' components of tarantula toxin activate the TRPV1 ion channel to cause pain. Toxins from plants, spiders and jellyfish that act on TRPV1 have been identified. Structural information about sites of interaction (toxin-binding sites on the Kv ion channel) have been evaluated. Toxin agonists such as resiniferatoxin and vanillotoxins were proposed to interact with a region of TRPV1 that is homologous to the 'voltage sensor' in the Kv1.2 ion channel, to open the channel and activate primary sensory nerves, causing pain (Cromer and McIntyre, 2007).
The voltage-sensor paddle is a crucial structural motif in voltage-activated potassium (K(v)) channels that has been proposed to move at the protein-lipid interface in response to changes in membrane voltage. Tarantula toxins like hanatoxin and SGTx1 inhibit K(v) channels by interacting with paddle motifs within the membrane (Milescu et al., 2007). These toxins can partition into membranes under physiologically relevant conditions, but the toxin-membrane interaction is not sufficient to inhibit K(v) channels. These require specific binding to the paddle motif.
This family belongs to the Conotoxin Superfamily.
|Cromer, B.A., and P. McIntyre. (2008). Painful toxins acting at TRPV1. Toxicon. 51: 163-73. |
|Diao, J., Y. Lin, J. Tang, and S. Liang. (2003). cDNA sequence analysis of seven peptide toxins from the spider Selenocosmia huwena. Toxicon. 42: 715-723.|
|Escoubas, P., S. Diochot, M.L. Célérier, T. Nakajima, and M. Lazdunski. (2002). Novel tarantula toxins for subtypes of voltage-dependent potassium channels in the Kv2 and Kv4 subfamilies. Mol. Pharmacol. 62: 48-57.|
|Henriques, S.T., E. Deplazes, N. Lawrence, O. Cheneval, S. Chaousis, M. Inserra, P. Thongyoo, G.F. King, A.E. Mark, I. Vetter, D.J. Craik, and C.I. Schroeder. (2016). Interaction of Tarantula Venom Peptide ProTx-II with Lipid Membranes is a Prerequisite for its Inhibition of Human Voltage-gated Sodium Channel NaV1.7. J. Biol. Chem. [Epub: Ahead of Print]|
|Lau, C.H., G.F. King, and M. Mobli. (2016). Molecular basis of the interaction between gating modifier spider toxins and the voltage sensor of voltage-gated ion channels. Sci Rep 6: 34333.|
|Liao, Z., C. Yuan, M. Deng, J. Li, J. Chen, Y. Yang, W. Hu, and S. Liang. (2006). Solution structure and functional characterization of jingzhaotoxin-XI: a novel gating modifier of both potassium and sodium channels. Biochemistry. 45: 15591-15600.|
|Middleton, R.E., V.A. Warren, R.L. Kraus, J.C. Hwang, C.J. Liu, G. Dai, R.M. Brochu, M.G. Kohler, Y.D. Gao, V.M. Garsky, M.J. Bogusky, J.T. Mehl, C.J. Cohen, and M.M. Smith. (2002). Two tarantula peptides inhibit activation of multiple sodium channels. Biochemistry 41: 14734-14747.|
|Milescu, M., J. Vobecky, S.H. Roh, S.H. Kim, H.J. Jung, J.I. Kim, and K.J. Swartz. (2007). Tarantula toxins interact with voltage sensors within lipid membranes. J. Gen. Physiol. 130: 497-511.|
|Ono, S., T. Kimura, and T. Kubo. (2011). Characterization of voltage-dependent calcium channel blocking peptides from the venom of the tarantula Grammostola rosea. Toxicon 58: 265-276.|
|Ozawa, S., T. Kimura, T. Nozaki, H. Harada, I. Shimada, and M. Osawa. (2015). Structural basis for the inhibition of voltage-dependent K+ channel by gating modifier toxin. Sci Rep 5: 14226.|
|Priest, B.T., K.M. Blumenthal, J.J. Smith, V.A. Warren, and M.M. Smith. (2007). ProTx-I and ProTx-II: gating modifiers of voltage-gated sodium channels. Toxicon 49: 194-201.|
|Ramracheya, R., C. Ward, M. Shigeto, J.N. Walker, S. Amisten, Q. Zhang, P.R. Johnson, P. Rorsman, and M. Braun. (2010). Membrane potential-dependent inactivation of voltage-gated ion channels in α-cells inhibits glucagon secretion from human islets. Diabetes 59: 2198-2208.|
|Smith, J.J., T.R. Cummins, S. Alphy, K.M. Blumenthal. (2007). Molecular interactions of the gating modifier toxin ProTx-II with Nav 1.5. J. Biol. Chem. 282.17; 12687-12697.|
|Takahashi, H., J.I. Kim, H.J. Min, K. Sato, K.J. Swartz, and I. Shimada. (2000). Solution structure of hanatoxin1, a gating modifier of voltage-dependent K+ channels: common surface features of gating modifier toxins. J. Mol. Biol. 297: 771-780.|
|Zhang, P.F., P. Chen, W.J. Hu, and S.P. Liang. (2003). Huwentoxin-V, a novel insecticidal peptide toxin from the spider Selenocosmia huwena, and a natural mutant of the toxin: indicates the key amino acid residues related to the biological activity. Toxicon. 42: 15-20.|
Processed protoxin-1 (ProTx1; ProTx-I) of 35 aas. Inhibits
voltage-gated calcium channels Cav3.1/CACNA1G, voltage-gated potassium
channels Kv2.1/KCNB1 and all sodium channels tested (Nav1.2/SCN2A,
Nav1.5/SCN5A, Nav1.7/SCN9A, and Nav1.8/SCN10A). Shifts the
voltage-dependence of channel activation to more positive potentials.
Most potent against Nav1.8/SCN10A (Middleton et al. 2002; Priest et al. 2007). A hydrophobic patch on the ProTx-II surface
anchors it at the cell surface in a position that optimizes interaction of the peptide
with the binding site on the voltage sensor domain. Binding of ProTx-II to the lipid membrane is directly linked to its potency as a hNaV1.7 channel
inhibitor (Henriques et al. 2016).
ProTx1 of Thrixopelma pruriens (P83480)
|8.B.5.2.1||Protoxin-2 (ProTx2; ProTx-II)||Tarantulas||ProTx2 of Thrixopelma pruriens (P83476)|
κ-Sparatoxin-Hv1b or heteropodatoxin 2 of 30 aas; It is an inhibitor
of voltage-gated potassium channels of the Kv4/KCND family (Ramracheya et al. 2010). Inhibition
of Kv4.3/KCND3 and Kv4.2/KCND2 is strongly voltage-dependent, while
inhibition of Kv4.1/KCND1 shows less voltage-dependence. Its binding
site may be near the potassium channel voltage sensor. This toxin also blocks
heteropda toxin 2 of Heteropoda venatoria (Brown huntsman spider) (Aranea venatoria)
|8.B.5.3.1||Vanillotoxin-1 (VaTx1) of Trinidad chevron tarantula (35 aas) (activates TRPV1 causing pain) (Cramer and McIntyre, 2008)||Spiders||VaTx1 of Psalmopoeus cambridgei (P0C244)|
|8.B.5.3.2||Vanillotoxin-3 (VaTx3) (34 aas; 50% identical to VATx1) (activates TRPV1 causing pain) (Cramer and McIntyre, 2008)||Spiders||VaTx3 of Psalmopoeus cambridgei (P0C246)|
|8.B.5.3.3||Heteroscodratoxin-1 (HMTx1) of the tarantula (35 aas) (blocks the voltage-gated K+ channels: Kv2.1 (KCNB1), Kv2.2 (KCNB2), Kv4.1 (KCND1), Kv4.2 (KCND2) and Kv4.3 (KCND3) causing convulsions and death in mice (Escoubas et al, 2002))||Spiders||HMTx1 of Heteroscodra maculata (P60992)|
|8.B.5.3.4||Huwentoxin-5 (HwTx5) precursor (86 aas) (insecticidal neurotoxin, Knottin-type; Diao et al., 2003; Zhang et al., 2003)||Spiders||HwTx5 of Ornithoctonus huwena (P61104)|
|8.B.5.3.5||Jingzhaotoxin-11 (JzTx11) precursor (86 aas) (Inhibits K+ and Na+ channels (e.g., Kv2.1, Kv4.1, Kv4.2, and Kv1.5)(Structure known: Liao et al., 2006))||Spiders||JzTx11 of Chilobrachys jingzhao (P0C247)|
|8.B.5.3.6||Hantotoxin-1 (HATx1) (35 aas) (Inhibits K+ and Ca2+ channels, e.g., Kv2.1, Kv4.2 and Cav2.1); (Structure known: Takahashi et al., 2000)||Spiders||Hanatoxin-1 of Grammostola rosea (tarantula) (P56852)|
ω-grammotoxin, SIA. Blocks P/Q type voltage-dependent calcium channels, Cav2.1 (Ono et al., 2011).
SIA of Grammostola rosea (P60590)
K+ channel blocker, a gating modifier toxin that inhibits by binding to the voltage sensor domain (VSD) of various VIC superfamily members, VSTx1 of 62 aas and 1 TMS (Ozawa et al. 2015). Many spider-venom peptides function as gating modifiers by
binding to the VSDs of voltage-gated channels and trapping them in a closed or open state (Lau et al. 2016). The toxin interacts with
residues in an aqueous cleft formed between the extracellular S1-S2 and S3-S4 loops of the VSD
whilst maintaining lipid interactions in the gaps formed between the S1-S4 and S2-S3 helices. The
resulting network of interactions increases the energetic barrier to the conformational changes
required for channel gating, and this is the mechanism by which gating modifier
toxins inhibit voltage-gated ion channels (Lau et al. 2016).
VSTx1 of Grammostola rosea (Chilean rose tarantula) (Grammostola spatulata)