Toxins from the wasp Bracon hebetor

Details Toxins from the wasp Bracon hebetor Toxins from the wasp Bracon hebetor

1997-05-12

2000-12-05

Carlson, Karen Cochrane

Chemistry: molecular biology and microbiology

Micro-organism, tissue cell culture or enzyme using process...

Recombinant dna technique included in method of making a...

435325, 4352523, C12N 500

Patent

active

061565369

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to novel insect toxins, DNA sequences encoding proteins which are toxic to insects, recombinant DNA constructs which comprise DNA sequences which encode a protein which is toxic to insects, and a biological control agent comprising said insect toxins, DNA sequences or recombinant DNA constructs.
The venoms of many social wasps have been extensively studied and are known to contain a potent array of biologically active amines, pain-producing neuropeptides, allergens and neurotoxins (Piek (1991) Toxicon, 29, 139-149). Much less understood are the venoms of solitary wasps, especially those which lead a parasitic lifestyle. Many solitary parasitic wasps prey upon insects and more than 250 species have been observed to paralyse their host (for review see Piek and Spanjer (1986) Venoms of the Hymenoptera, T Piek (Ed.) Academic Press, London pp161-307). Many of these species are in the family Braconidae. The majority of braconid wasps are primary parasites. Adults lay their eggs almost exclusively in or on other insects and, after hatching, the wasp larvae feed upon their host. One braconid species that has attracted attention is Bracon hebetor (Bracon=Microbracon=Habrobracon). Bracon hebetor (B. hebetor) is a small (3 mm) parasite of Lepidoptera larvae which have a cryptic, or cocooning, lifestyle. Adult female wasps deposit eggs on the outside of host larvae while simultaneously injecting a paralysing venom. Within minutes, the host larvae become uncoordinated and eventually suffer complete paralysis. Although not directly fatal, this paralysis is permanent and immobilises the insect until the wasp larvae emerge to feed upon their host. The venom of B. hebetor possesses an extremely potent paralysing activity. In larvae of the greater waxmoth, Galleria mellonella (G. mellonella), it has been estimated that complete and permanent paralysis occurs at levels of 1 part venom to 200,000,000 parts host haemolypmph (Beard (1952) Conn. Agric. Exp. Stn. New Haven Bulletin, 562, 27). Furthermore, the venom shows selective toxicity towards insects and between insect orders. Spider, crayfish, frog, rat and guinea-pig neuromuscular preparations all appear to be insensitive to the venom (Rathmayer and Walther (1976) Animal, Plant and Microbial Toxins, 2, Plenum Press, New York, 299-307; Deitmer (1973) Die Wirkung des Griffes der Schlupf-wespe Habrobracon Say auf die neuromuskulare Ubertragung am sartoriusmuskel des Frosches, Diplomarbeit, Universitat Bonn).
The paralysing component of B. hebetor venom is thought to act by presynaptically blocking excitatory glutamatergic transmission at neuromuscular junctions, possibly by inhibiting the release of synaptic vesicles (Walther and Reinecke (1983) Neuroscience, 9, 213-224; Piek and Mantel (1970) Comp. Gen. Pharmcol, 1, 87-92; Piek (1966) J. Insect Physiol., 12, 561-568).
Venoms from many arthropods that prey on insects have been found to contain toxins which selectively act on insects. Such insect-selective neurotoxins can be important molecular tools to study insect neurobiology. The mode of action and insect-selectivity of B. hebetor toxin predicts that it could be useful in the study of neuromuscular transmission in Lepidoptera and in the study of vesicle release at Lepidopteran neuromuscular junctions. It will also be appreciated that such insect selectivity is very advantageous in the control of insect pests. However, since the published information on proteinaceous toxins from B. hebetor suggests that multiple toxins may exist it was first necessary to purify and characterise a toxin that had high neurotoxic activity to Lepidopteran larvae. We have now purified and characterised two neurotoxic proteins, which for ease of reference only have been designated bracon toxin 1 and 2 (hereinafter BrhTX-1, and BrhTX-2).
Thus, according to one aspect of the present invention there is provided an insect toxin comprising four polypeptide subunits, wherein the polypeptide subunits have the N terminal amino acid sequences shown in Sequence ID Nos. 1, 2, 3

REFERENCES:
patent: 5874298 (1999-02-01), Johnson et al.
"Purification and Characterization of Insecticidal Toxins from Venom Glads of the Parasitic Wasp, Bracon Hebetor,"Gary Quistad et al., Insect Biochem. Molec. Biol., vol. 24, No. 10, pp. 955-961, 1994.
Chemical Abstract vol. 108, 1988, p. 248, 108: 50986v "Effect of the Toxin from the Venom of the Braconid Habrobracon Hebetor (Say), on Insect Neuromuscular Transmission," T. I. Slavnova et al.
"Characterization of Two Paralysing Protein Toxins (A-MTX and B-MTX), Isolated from a Homogenate of the Wasp Microbracon Hebetor (Say), "B. J. Visser et al., Comp. Biochem. Physio. V75B, No. 3, pp. 523-530, 1983.

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