8.B.3 The Huwentoxin-1 (Huwentoxin-1) Family
Huwentoxin-1 is an 81 aa neurotoxin precursor that is a Ca2+ channel inhibitor (Diao et al., 2003). Huwentoxin-1 is a lethal neurotoxin that binds to the nicotinic acetylcholine receptor and blocks neuromuscular transmission. It possesses presynaptic activity that affects the release of neurotransmitters from autonomic nerve endings of both cholinergic and adrenergic neuroeffector junctions. It selectively inhibits N-type calcium channels and has only very weak effects on L-type calcium channel.
Hainantoxin-4 from the Chinese bird spider, Selenocosmia (Ornithoctonus) hainana, is a 35 aa processed peptide neurotoxin. It selectively blocks neuronal tetrodotoxin-sensitive voltage-gated Na+ channels as a monomer (Liu et al., 2002; Xu et al., 2005). Structures of hainantoxins have been determined by NMR (Li et al., 2004; Qu et al., 1997). These mature toxins each have a disulfide bridge and are amidated at their C-termini. Huwentoxin-IV is an inhibitor cystine knot peptide from Chinese tarantula Ornithoctonus huwena venom that blocks tetrodotoxin-sensitive voltage-gated sodium channels from mammalian sensory neurons (Xiao et al., 2008). The solution structure has been solved (Peng et al., 2002).
Huwentoxin-1 precursor of Selenocosmia huwena (81 aas; P56676)
Hainantoxin-4 of Selenocosmia hainana (35 aas; P83471)
Huwentoxin-4 precursor of 89 aas. This lethal neurotoxin acts selectively on tetrodotoxin-sensitive (TTX-S) voltage-gated sodium channels. A heterobivalent ligand (mu-conotoxin KIIIA (TC# 8.B.28.1.4), which occludes the pore of the NaV channels, and an analogue of huwentoxin-IV, a spider-venom peptide that allosterically modulates channel gating) slows ligand dissociation and enhances potency (Peschel et al. 2020).
Huwentoxin-4 precursor of Ornithoctonus huwena (Chinese bird spider) (Selenocosmia huwena) (Haplopelma schmidti) (P83303)
Phrixotoxin 3. (β-stranded β-Theraphotoxin-Ps1A) Na+-channel blocker (Ono et al., 2011).
Phrixotoxin 3 of Paraphysa scrofa (P84510)
Jingzhaotoxin F7-10.36 of 34 aas. Interacts with and activates Kv2.1 and Nav1.5 channels
(Tao et al. 2013; Tao et al. 2013).
Jingzhaotoxin F7 of Chilobrachys guangxiensis (chilobrachys jingzhao; chinese earth tiger tarantula)
U24-Theraphotoxin-Cgla (U24-TRTx-Cg1a) or Jingzhaotoxin-27 (JZTx-27) of 79 aas and 1 N-terminal TMS. JZTx-27 traps the voltage sensor of NsVBa (TC# 1,A,1,14,8) in one of the deactivated states. In mammalian NaVs, JZTx-27 preferably inhibits the inactivation of NaV1.5 by targeting the fourth transmembrane domain. This peptide antagonist preferentially targets prokaryotic NaVs, but it stabilizes the NsVBa voltage sensor in the deactivated state (Tang et al. 2017).
JZTx-27 of Chilobrachys guangxiensis (Chinese earth tiger tarantula) (Chilobrachys jingzhao)
GsMTx4 of 82 aas and one N-terminal TMS. This cationic hydrophobic peptide inhibits a lot of different Na+ and K+ channels and has antimicrobial activity (Gnanasambandam et al. 2017). It blocks mechanosensitive ion channels (also named stretch-activated channels or SACs), without having effect on whole-cell voltage-sensitive currents. Acts by partitioning into the membrane and perturbing the interface between the channel and the lipid bilayer without necessarily being in physical contact with the channel. Inhibits atrial fibrillation as well as the membrane motor of outer hair cells at low doses. It also binds to the voltage sensor of voltage-gated potassium channels from the archaebacterium Aeropyrum pernix (KvAP) without affecting channel gating. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin (Gnanasambandam et al. 2017).
GsMTx4 of Grammostola rosea (Chilean rose tarantula) (Grammostola spatulata)