"Soft"-cuticle protein secondary structure as revealed by FT-Raman, ATR FT-IR and CD spectroscopy

The nature of the interaction of insect cuticular proteins and chitin is un known even though about half of the cuticular proteins sequenced thus far s hare a consensus region that has been predicted to be the site of chitin bi nding. We previously predicted the preponderance of a P-pleated sheet in th e consensus region and proposed its responsibility for the formation of hel icoidal cuticle (Iconomidou et al., Insect Biochem. Mel. Biol. 29 (1999) 28 5). In this study, we examined experimentally the secondary structure of in tact and guanidine hydrochloride extracted cuticle and the cuticular protei n extract. The studied cuticle came from the larval dorsal abdomen of the l epidopteran Hyalophora cecropia, a classical example of;"soft" cuticle. Ana lysis with FT-Raman, ATR FT-IR and CD spectroscopy indicates that antiparal lel P-pleated sheet is the predominant molecular conformation of "soft-cuti cle" proteins both in situ in the cuticle and following extraction. It seem s that this conformation dictates the modes of chitin-protein interaction i n cuticle, in agreement with earlier proposals (Atkins, J. Biosci. 8 (1985) 375). (C) 2001 Elsevier Science Ltd. All rights reserved.