title: Silk fiber assembly studied by synchrotron radiation SAXS/WAXS and Raman spectroscopy.
abstract: We have characterized the steps involved in silk assembly from the protein solution into beta-type fibers by a combination of small-angle and wide-angle X-ray scattering and Raman spectroscopy. The aggregation process was studied in a concentric flow microfluidic cell, which allows mimicking the spinning duct. The fibroin molecule in solution shows an elongated shape with a maximum diameter of 38 nm. During the pH-driven initial assembly step, large-scale aggregates of fibroin molecules with a maximum diameter of about 260 nm are formed. Raman spectroscopy on the dried, fibrous material shows a principally alpha-helical silk I secondary structure, which is transformed gradually into beta-type silk II by increasing immersion times in water. The formation of crystalline beta-sheet domains within the fiber is confirmed by wide-angle X-ray scattering. The assembly process resembles the peptide condensation-ordering model proposed for amyloid cross-beta formation.
authors.affiliation: European Synchrotron Radiation Facility, B.P. 220, F-38043 Grenoble Cedex, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Martel
authors.forename: Manfred
authors.initials: M
authors.lastname: Burghammer
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Davies
authors.forename: Emanuela
authors.initials: E
authors.lastname: Di Cola
authors.forename: Charlotte
authors.initials: C
authors.lastname: Vendrely
authors.forename: Christian
authors.initials: C
authors.lastname: Riekel
mesh_terms: D000818:Animals; D012831:Bombyx / Q000737:chemistry; D008958:Models, Molecular; D047011:Silk / Q000737:chemistry*; D013057:Spectrum Analysis; D017356:Synchrotrons
chemical_list: D047011:Silk