title: Spectroscopic studies of Manduca sexta and Sesamia nonagrioides chorion protein structure.
abstract: The secondary structure of Manduca sexta and Sesamia nonagrioides chorion proteins has been studied in intact chorions using laser-Raman and Fourier transform infra-red (FTIR) spectroscopy and in a solution containing extracted and reassembled chorion proteins using circular dichroism (CD) spectroscopy. Laser-Raman and IR spectra suggest the predominance 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 can best be interpreted as resulting from abundant antiparallel beta-pleated sheet structure. Analysis of the amide I band suggests that chorion 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 spectroscopy 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 beta-sheet structure of chorion proteins may exist in solution and dictate the aggregation and polymerization process in vivo.
authors.affiliation: Department of Biochemistry, Cell and Molecular Biology and Genetics, University of Athens, Greece.
authors.forename: C C
authors.initials: CC
authors.lastname: Orfanidou
authors.forename: S J
authors.initials: SJ
authors.lastname: Hamodrakas
authors.forename: G D
authors.initials: GD
authors.lastname: Chryssikos
authors.forename: E I
authors.initials: EI
authors.lastname: Kamitsos
authors.forename: S E
authors.initials: SE
authors.lastname: Wellman
authors.forename: S T
authors.initials: ST
authors.lastname: Case
mesh_terms: D000818:Animals; D002823:Chorion / Q000737:chemistry*; D002942:Circular Dichroism; D005260:Female; D007915:Lepidoptera / Q000737:chemistry*; D018402:Manduca / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman
chemical_list: D011506:Proteins