MONGOOSES are renowned for their ability to kill snakes, a reputation due in
no small part to Rudyard Kipling’s The Jungle Book. Now a team of
scientists in Israel has discovered that it is not just by moving quickly that
these small mammals manage to evade the lethal bite of a snake. They are also
unaffected by snake venom.
The active ingredient most commonly found in snake venoms, alpha-neurotoxin,
works by attaching itself to acetylcholine receptor molecules on the surface of
muscle cells. These receptors are designed to receive messages from nerves which
tell the muscles to contract or relax. But alpha-neurotoxin blocks the messages,
paralysing and ultimately killing the victim.
Sara Fuchs of the Immunology Department at the Weizmann Institute in Israel,
who is an expert on the physiology of the junctions between nerves and muscles,
studied the molecular structures of acetylcholine receptors and found that those
in mongooses and snakes are shaped so that it is impossible for snake venom to
attach to them. The receptors can still transfer messages from nerves to
muscles, and are unaffected by snake venom.
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“We looked carefully at the receptor molecules on muscles in the mongoose and
found the structure was slightly different from receptors in mammals, like mice,
that do get killed by snakebite,” Fuchs explains. “Similar changes occur in
snakes so that snakes don’t get poisoned by their own toxins.” In the lab, Fuchs
and her team also succeeded in changing the structure of mongoose receptors to
resemble those in animals which are sensitive to snake venom. “In terms of
muscle receptors, we could convert a mongoose into a mouse.”
Fuchs is now looking at other snake toxins to see if mongooses and snakes are
protected from their effects by similar mechanisms. She believes that this work,
and the neurotoxin research, could eventually lead to the production of new
anti-venom drugs that would use the active parts of mongoose or snake receptor
molecules and be more effective and safer to use than current drugs.
David Warrell at the Centre for Tropical Medicine at the University of Oxford
says Fuchs’s work is “very interesting, because it reveals one of probably many
mechanisms by which animals exposed to snake venom evade the specific action of
the venom. The receptors seem to have changed their structures under
evolutionary pressure.” But he warns that developing new antivenom drugs would
be “far from straightforward”.