title: Conformational transitions in model silk peptides.
abstract: Protein structural transitions and beta-sheet formation are a common problem both in vivo and in vitro and are of critical relevance in disparate areas such as protein processing and beta-amyloid and prion behavior. Silks provide a "databank" of well-characterized polymorphic sequences, acting as a window onto structural transitions. Peptides with conformationally polymorphic silk-like sequences, expected to exhibit an intractable beta-sheet form, were characterized using Fourier transform infrared spectroscopy, circular dichroism, and electron diffraction. Polymorphs resembling the silk I, silk II (beta-sheet), and silk III (threefold polyglycine II-like helix) crystal structures were identified for the peptide fibroin C (GAGAGS repetitive sequence). Two peptides based on silk amorphous sequences, fibroin A (GAGAGY) and fibroin V (GDVGGAGATGGS), crystallized as silk I under most conditions. Methanol treatment of fibroin A resulted in a gradual transition from silk I to silk II, with an intermediate state involving a high proportion of beta-turns. Attenuated total reflectance Fourier transform infrared spectroscopy has been used to observe conformational changes as the peptides adsorb from solution onto a hydrophobic surface. Fibroin C has a beta-strand structure in solution but adopts a silk I-like structure upon adsorption, which when dried on the ZnSe crystal contains silk III crystallites.
authors.affiliation: Department of Chemical Engineering and Biotechnology Center, Tufts University, Medford, Massachusetts 02155 USA.
authors.forename: D
authors.initials: D
authors.lastname: Wilson
authors.forename: R
authors.initials: R
authors.lastname: Valluzzi
authors.forename: D
authors.initials: D
authors.lastname: Kaplan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D012831:Bombyx; D002942:Circular Dichroism; D005349:Fibroins / Q000737:chemistry; D019476:Insect Proteins / Q000737:chemistry* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D047011:Silk; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D019476:Insect Proteins; D010455:Peptides; D047011:Silk; D012996:Solutions; D005349:Fibroins