Denmotoxin, a Three-finger Toxin from the Colubrid Snake Boiga dendrophila (Mangrove Catsnake) with Bird-specific Activity

Abstract

Boiga dendrophila (mangrove catsnake) is a colubrid snake that lives in Southeast Asian lowland rainforests and mangrove swamps and that preys primarily on birds. We have isolated, purified, and sequenced a novel toxin from its venom, which we named denmotoxin. It is a monomeric polypeptide of 77 amino acid residues with five disulfide bridges. In organ bath experiments, it displayed potent postsynaptic neuromuscular activity and irreversibly inhibited indirectly stimulated twitches in chick biventer cervicis nerve-muscle preparations. In contrast, it induced much smaller and readily reversible inhibition of electrically induced twitches in mouse hemidiaphragm nerve-muscle preparations. More precisely, the chick muscle ␣ 1 ␤␥␦-nicotinic acetylcholine receptor was 100-fold more susceptible compared with the mouse receptor. These data indicate that denmotoxin has a bird-specific postsynaptic activity. We chemically synthesized denmotoxin, crystallized it, and solved its crystal structure at 1.9 Å by the molecular replacement method. The toxin structure adopts a non-conventional three-finger fold with an additional (fifth) disulfide bond in the first loop and seven additional residues at its N terminus, which is blocked by a pyroglutamic acid residue. This is the first crystal structure of a three-finger toxin from colubrid snake venom and the first fully characterized bird-specific toxin. Denmotoxin illustrates the relationship between toxin specificity and the primary prey type that constitutes the snake's diet. Three-finger toxins (3FTXs)3 form one of the most abundant, well recognized families of snake venom proteins. They share a similar structure and are characterized by three ␤-stranded finger-like loops, emerging from a globular core and stabilized by four conserved disulfide bridges. An additional disulfide linkage may sometimes be present in the first (non-conventional toxins) or second (long-chain ␣-neurotoxins and -toxins) loop (1-5). All 3FTXs are monomers except for -toxins, which are noncovalent homodimers isolated from Bungarus venoms. Minor structural differences in the three-finger fold, viz. the number of ␤-strands, overall morphology of the loops, and differential lengths of turns or C-terminal tails (6), lead to the recognition of varied targets and modulate the toxicity and specificity (7). Hence, 3FTXs affect a broad range of molecular targets, including ␣ 1 -nicotinic acetylcholine receptors (nAChRs; short-and longchain ␣-neurotoxins), ␣ 7 -nAChRs (long-chain ␣-neurotoxins), and ␣ 3 -and ␣ 4 -nAChRs (-toxins) (4, 5); muscarinic acetylcholine receptors (muscarinic toxins) (8); L-type calcium channels (calciseptine and FS2 toxin) (9, 10); integrin ␣ IIb ␤ 3 (dendroaspin) (11, 12); integrin ␣ v ␤ 3 (cardiotoxin A5) (13); acetylcholinesterase (fasciculins) (14); phospholipids and glycosphingolipids (cardiotoxins) (15); and blood coagulation protein factor VIIa (16). As the interaction with such a broad spectrum of target proteins results in a variety of pharmacological effects, the understanding...

Structural and Functional Characterization of a Novel Homodimeric Three-finger Neurotoxin from the Venom of Ophiophagus hannah (King Cobra)

“…Identification was further confirmed by N-terminal sequencing of the first 36 residues, which matched the cDNA sequence of the MTLP-3 homolog (20). This protein was found to be a homodimer (see below) and hence was renamed as haditoxin (O. hannah dimeric neurotoxin) following the nomenclature of dimeric 3FTxs (12,13).…”

“…Chick Biventer Cervicis Muscle (CBCM) Preparations-The CBCM nerve-skeletal muscle preparation (39) was isolated from chicks (6 days old) and mounted in the organ bath chamber under similar experimental conditions as described previously (12,31). The effect of haditoxin (0.05-5 M; n ϭ 3) or ␣-bungarotoxin (0.01-1.0 M; n ϭ 3) on nerve-evoked twitch responses of the CBCM were studied.…”

“…They are most commonly found in the venoms of elapid and hydrophiid snakes. Recently, our laboratory has also demonstrated the presence of 3FTxs from colubrid venoms (12,13), and 3FTx transcripts have been found in the venom gland transcriptome of viperid snakes (14,15). The proteins in this family of toxins share a common structural scaffold of three ␤-sheeted loops emerging from a central core (11,16).…”

“…Muscarinic toxin 1, isolated from the venom of Dendroaspis angusticeps, interacts with mAChR subtype 1 (M1) (29), whereas muscarinic toxin 3 (MT3), isolated from the same snake, interacts with M4 mAChRs (30). In recent years, new 3FTxs with distinct and novel receptor specificities have been characterized and added to this growing library (12,13,(31)(32)(33)(34)(35)(36), justifying their usefulness as pharmacological tools to dissect the cholinergic circuitry to understand the role of individual receptor subtypes or offer clues to the rational design of specific therapeutics.…”

Two color morphs of the pelagic yellow-bellied sea snake, Pelamis platura, from different locations of Costa Rica: Snake venomics, toxicity, and neutralization by antivenom

“…Thus, although the results indicated that the major PLA 2 eluted in peak 9 (which accounts for ~20% of the total venom proteins) was not lethal to mice, the possibility that this protein exhibits taxon-specific activity, as reported for other toxins [83][84][85][86][87], requires future detailed investigation. Finally, of relevance from a clinical standpoint, the sea snake antivenom manufactured by CSL in Australia using the venom of E. schistosa displays sufficient immunological cross-reactivity to provide protection from the lethal effects of P.…”