Secret behind hard exoskeletons, spreading wing...( A study by Gottfried Fraenkel in 1962 s...)

All insects must shed their old outer skin or cuticle periodically in order to grow. The new outer shell then hardens and its color darkens. Both processes take place through the activation of a series of five hormones. The structure, genetic sequence and biochemical properties of four of these hormones were known since 1990; that of the fifth, bursicon, was not.

Using biochemical methods, the researchers set out to determine bursicon's genetic sequence and molecular structure and also to confirm that it indeed triggered the hardening process.

In the first phase of the work, the team went to work to determine the genetic sequence of bursicon. Using cockroaches, Honegger's students were able to collect and purify a small sample of the hormone. They sent this sample to a laboratory at Harvard University that chemically sequenced it and sent back four short amino acid sequences of which the sample was composed.

Using this sequence, Dewey, a post-doctoral researcher in Honegger's laboratory, ran searches on the genome of the fruit fly and found that three of the four sequences matched the sequence of the fruit fly gene CG13419. She subsequently compared the sequence to known genomes for other insects and also found matches, leading the team to determine that bursicon has the same genetic sequence across species.

The researchers then used the sequencing information to determine the structure of the bursicon molecule. They found that bursicon's structure makes it a member of a group of molecules known as the cystine knot proteins. Cystine knot proteins are so known due to their molecular structure, repeated across mammalian species, of three loops of amino acids linked together in a
'"/>

Contact: Melanie Catania
melanie.catania@vanderbilt.edu
615-322-7970
Vanderbilt University
12-Jul-2004