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).