SPECTROSCOPIC STUDIES OF MANDUCA-SEXTA AND SESAMIA NONAGRIOIDES CHORION PROTEIN-STRUCTURE

The secondary structure of Manduca sexta and Sesamia nonagrioides chor ion proteins has been studied in intact chorions using laser-Raman and Fourier transform infra-red (FTIR) spectroscopy and in a solution con taining extracted and reassembled chorion proteins using circular dich roism (CD) spectroscopy. Laser-Raman and IR spectra suggest the predom inance of antiparallel beta-pleated sheet structure in intact chorion proteins of both Lepidoptera species. The bands at 1673, 1674 cm(-1) ( amide I) and 1234-1238 cm(-1) (amide III) in the laser-Raman spectra c an best be interpreted as resulting from abundant antiparallel beta-pl eated sheet structure. Analysis of the amide I band suggests that chor ion proteins consist of 60-70% antiparallel beta-pleated sheet and 30- 40% beta-turns. Supporting evidence for the prevalence of antiparallel beta-pleated sheet in chorion proteins was supplied using FTIR spectr oscopy by the observation of a very intense absorption band at 1635 cm (-1) (amide I) and of a weak band at 1530, 1525 cm(-1) (amide II) from chorions of both species. Surprisingly, analysis of the CD spectra of extracted and reassembled chorion proteins suggests that, in solution , they retain a regular secondary structure most probably dominated by beta-pleated sheet. We therefore suggest that the prominent regular b eta-sheet structure of chorion proteins may exist in solution and dict ate the aggregation and polymerization process in vivo.