United Kingdom
March 12, 2007
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”
The research has been published in the 9th March issue of
The Journal of Molecular Biology Volume 366 Issue 5 pages
1558 – 1568. The paper is titled “Structural Characterisation
of the Insecticidal Toxin XptA1, Reveals a 1.15 MDa Tetramer
with a Cage-like Structure”. |
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