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Kansas State University researchers think their discovery of the enzyme
involved in the hardening of a beetle's exoskeleton or cuticle could lead
not only to better pest control, but also help create similar strong,
lightweight materials for use in aircraft and armor, August 2005 by Jennifer
Newberry.

After a beetle first molts, its exoskeleton is soft and hydrated. Somehow,
it dries out and forms a hard, stiff exoskeleton. Since the 1940s,
scientists have wondered which enzyme among several possible candidates was
involved in the hardening process.

The K-State researchers have found that by knocking out an enzyme called
laccase-2, cuticle tanning, the process of hardening and pigmentation, can
be prevented in the red flour beetle, Tribolium castaneum.

A paper, to be released this week in the Proceedings of the National Academy
of Sciences, presents the research results. The K-State researchers are
Yasuyuki Arakane, research associate in biochemistry; Subbaratnam
Muthukrishnan, professor of biochemistry; Richard Beeman, adjunct professor
of entomology; Michael Kanost, professor and head of the department of
biochemistry; and Karl Kramer, adjunct professor emeritus of biochemistry.

Kramer said K-State researchers wanted to find out what happens between the
times when the cuticle is soft and when it is hard. They studied the
cuticle's composition and how the components interacted to give it
stiffness, flexibility and lightness. The main components in the cuticle are
proteins and chitin, which also are found in crustaceans and other
invertebrates.

The researchers knew one of two classes of oxidative enzymes, tyrosinases or
laccases, is likely responsible for catalyzing the exoskeleton's hardening
by cross-linking cuticular proteins, Kanost said.

"When we knocked out tyrosinase, everything was normal," Kramer said. "When
we knocked out laccase-2, we prevented tanning from taking place."

When the laccase-2 gene was not expressed, the newly formed cuticle remained
soft and white instead of becoming hard and dark-coloured. These results
indicated which protein was responsible for the hard shell's formation,
Kanost said.

The identification of laccase-2 as the catalyst for cuticle tanning opens up
possibilities of targeting this protein as a way of weakening the beetle's
physical defences against mechanical, chemical and biological injuries,
Muthukrishnan said. Better insecticides could be developed as a result of
having a more insect-specific target like laccase-2, Kramer said.

"Gaining knowledge about a molecular process required for insect
development, but absent from humans and other vertebrate animals, such as
cuticle tanning, may be useful for developing new, bio-rational methods for
controlling pest insect populations," Kanost said.

Armed with this new information, a number of practical applications are
possible. Materials based on the chemistry of the insect exoskeleton could
be developed to make lightweight materials for aircraft and military armour,
Kramer said.

"I sometimes speculate that we might help K-State coach Bill Snyder develop
better football helmets and shoulder pads for his players," he said.

Collaborative research with scientists at the University of Kansas is in the
beginning stages to analyse quantitatively the mechanical properties of
insect cuticles and to perform cuticle protein cross-linking experiments
that are catalysed by insect laccase, Kramer said. KU scientists will test
the strength of the synthetic cross-linked biopolymers that are created.
This could be used for the development of strong, lightweight materials.

Both Beeman and Kramer also work at the Grain Marketing and Production
Research Center, Agricultural Research Service, United States Department of
Agriculture, in Manhattan.

[www.k-state.edu]

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