Secret of worm's poison pill box protein could
produce new natural insecticide
Researchers at the University of Warwick have
discovered how a protein from a bacterium acts like a cunningly
designed poison pill box that could now be used as a basis of a new
range of natural insecticides. It had been known that nematode worms
can infect and kill insect pests with the help of a bacterium which
they harbour inside their intestine.
The bacterium uses a protein (XptA1) a toxin which
helps the nematode to kill and feed on the dead body of the insect.
The toxin not only kills the target insect but prevents other
predators from eating the body giving free reign to the nematode worms
to consume it, multiply and move on. However, until now, researchers
had little idea of the make up of XptA1 and thus how it worked. The
research team, based at the University of Warwick’s horticultural
research arm Warwick HRI, have now been able to reveal the shape of
the protein XptA1 and discovered a number of properties that make it a
particularly efficient natural insecticide and possible alternative to
some commercial insecticides that are facing increased resistance in
the insect populations they target.
The researchers at Warwick HRI, together with a
team of colleagues with expertise in the Structural Biology group in
Biological Sciences and in Chemistry at The University of Warwick, as
well as Coventry and Nottingham Universities, found that the protein
was formed from four sub units in the shape of a hollow cage or box
which is configured to bind well to part of a caterpillar’s gut called
"Brush Border Membrane Vesicles" (BBMV).
The XptA1 protein seemed to specifically target the
BBMV of caterpillars Pieris Brassicae – (The cabbage white butterfly
caterpillar which are pests for many growers). The hollow box
structure appears to be a key element of the protein’s design. The
hollow shape allows the protein to act as a receptacle for two other
proteins (in the case of XptA1 these are XptB1 and XptC1). This forms
a poison "complex" which makes the XptA1 300 times more toxic to the
caterpillars than it would be by itself. As well as helping collect
together the three proteins and attach them to the insect’s gut the
researchers think that the box shape of the XptA1 protein possibly
also helps protect the poison complex from the acid attack they would
face from the high pH values in the insect gut. The researchers also
discovered that, while XptA1 was highly selective in that it bound to
the cabbage white butterfly caterpillar, there were variants of this
family of toxic proteins (such as XptA2) that targeted other insects.
Dr Sarah Lee from the University of Warwick said: "This
research gives us crucial new insights into a family of naturally
occurring proteins that are toxic to a number of insect pests. They
offer an alternative to current commercial protein based insect toxins
have been in use for 40 years and are now starting to meet some
resistance. This potential new family of protein based insecticides
would overcome such resistance as they operate in an entirely
different way"
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