By David N. Leff
Australia's funnel-web spider has been known to kill people. Its stout, venom-filled fangs can penetrate a fingernail.
Luckily, that spider (Hadronyche versuta) fancies insects more than humans in its daily diet. Fortunately, too, an anti-venom antidote released in 1980 put a sudden stop to the deaths of Homo sapiens racked up by the funnel-web tenant.
That formidable arachnid's range is scrubland in eastern Australia, from Queensland to Tasmania. Many an inadvertent weekend gardener has discovered that its habitat includes the topsoil of suburban Sydney backyards. The glossy black, hairy-legged spider digs a foot-long burrow, lines it with fine-mesh web, and lies in wait at the entrance, or sallies forth to find insect prey.
Many an Australian and American crop scientist would like to see one insect in particular become prey to H. versuta's lethal toxin. That targeted bug is the cotton bollworm, larva of a moth called Helicoverpa armigera. This big, brown, striped caterpillar bores its way to the heart of a cotton boll before it opens, and devours the fiber from within.
"It's one of the world's most economically devastating agricultural pests," observed protein chemist Glenn King, "and one of the most difficult to control." King, who heads the Protein Structural and Engineering Group at the University of Sydney, is senior author of a paper in the July issue of Nature Structural Biology. Its title: "The structure of a novel insecticidal neurotoxin omega-atracotoxin from the venom of an Australian funnel-web spider."
Since early 1995, King and his co-authors have been working to unravel the complex molecular biology of the funnel-web spider's venom. "We knew from the very beginning," he told BioWorld Today, "that its toxin would be useful agriculturally. That is the primary reason we got involved."
That deadly chemical cocktail consists of at least 45 different molecules -- and still counting. Right now, the teams' spotlight is on two of those proteins in particular. "One of them," King said, "is the neurotoxin that kills insects; the second kills us and other primates."
The insect-slaying venom fraction, as the journal paper reports, is a peptide 37-amino-acids long, with an atomic mass of 4,050 Daltons. Tests by other Australian investigators in the early 1990s verified that it was highly, and lethally, specific in vitro to the H. armigera cotton bollworm, but harmless to newborn mice.
King and his group tackled the task of analyzing the fraction's molecular structure as a first step toward elucidating its precise insecticidal function.
"The amounts of this particular venom that we could isolate," he recounted, "were way too small to do our structural study, so we chemically synthesized the protein, and folded it up in the correct manner."
Recently, they began dissecting the second toxin fraction, King said, "and have just submitted another paper on that one, which kills us instead of insects."
Calcium Ions For Bugs; Sodium For Folks
The structure-function differences between the two, he observed, "are interesting. The insect-killing one works specifically on calcium ion channels. It blocks these in insect neurons, but doesn't do so in humans and other mammals."
He continued: "On the other hand, the component that kills us seems to work specifically on our sodium channels, in primate brains."
He continued: "The insect-directed toxin blocks the calcium channel. The toxin that affects us actually holds our sodium channel open, preventing it from closing. So you get this release of sodium, and that screws up the conduction of the nerve impulse."
King foresees three possible ways to go in getting the spider's insect-specific poison into or onto cotton bollworms:
"The first way," he suggested, "is to engineer it into the cotton plant, as Monsanto has done with its Bt cotton crop. They've taken the gene from that Bacillus thuringiensis toxin and put it in the seed. We could do exactly the same thing with our H. versuta molecule.
"The problem I see long-term with that," he continued, "is that the bugs that are naturally resistant to Bt are going to get resistant very quickly to our spider venom product too.
"Another way to go," King went on, "would be to engineer the gene for the toxin into an insect-specific virus, baculovirus, for example, and release it as a spray.
"The way that I prefer," King said, "which is the way farmers have been doing for ages, and managing their crops very well, is they rotate a range of chemical pesticides. The problem with that is that a lot of chemical pesticides are environmentally dangerous.
"So if we can base a chemical insecticide on our peptide, which seems to be insect-specific, it shouldn't have the same environmental disadvantages that most of the common pesticides do."
Right now, King is trying to "trim down the molecule to a smaller size. We've had some success, and hope by the end of the year to have some idea of the minimum part of the sequence that's important for its function."
FMC Cites Criteria For Collaboration
Pursuing this point, King added: "One company in particular that we're very interested in talking to is FMC Corp., up in Princeton, N.J. In fact, they've got our confidentiality agreement right now, and just as soon as that's signed, I'm going to go up and have a chat with them."
King is currently on sabbatical at the University of Connecticut's Health Center, in Farmington.
FMC's director of commercial development is Gert Volpp. Commenting on the Australians' spider venom molecule, he told BioWorld Today, "If what they are working on turns out to be a proteinaceous material, it would not readily penetrate the insect's skin, and so would be of limited utility. If that is the direction one would have to head," he continued, "FMC and myself would be not interested, or not very much interested."
He added: "We are not in the business of genetically modifying plants.
"On the other hand," Volpp concluded, "if the material lends itself to synthesis, or can be made by fermentation, but would be of a kind that is tractable as a chemical pesticide, and could be applied not only to plants but, let's say, ants or termites or cockroaches -- you can incorporate such a material in bait and apply it -- then, yes, we would be interested in looking at it in detail." *