Vibrational infrared conformational studies of model peptides representing the semicrystalline domains of Bombyx mori silk fibroin

✍ Scribed by Paola Taddei; Patrizia Monti

• Book ID: 102760705
• Publisher: Wiley (John Wiley & Sons)
• Year: 2005
• Tongue: English
• Weight: 521 KB
• Volume: 78
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.20275

✦ Synopsis

Abstract

The structural organization of Bombyx mori silk fibroin was investigated by infrared (IR) spectroscopy. To this aim, (AG)~15~ and other model peptides of varying chain length, containing tyrosine (Y), valine (V), and serine (S) in the basic (AG)~n~ sequence were synthesized by the solid phase method and their spectroscopic properties were determined. Both the position and the relative content of Y, V, and S residues in the (AG)~n~ model system appeared critical in determining the preferred conformation, i.e., silk I, silk II, and unordered structures. Curve fitting analysis in the amide I range showed that the model peptides with prevailing silk II structure displayed different β‐sheet content, which was dependent on the degree of interruption of the (AG)~n~ sequence. In this regard, the bands at about 1000 and 980 cm^−1^, specifically assigned to the AG sequence of the B. mori silk fibroin chain, were identified as marker of the degree of interruption of the (AG)~n~ sequence.

A stable silk I structure was observed only when the Y residue was located near the chain terminus, while a silk I → silk II conformational transition occurred when it was positioned in the central region of the peptide.

Analysis of the second‐derivative spectra in the amide I range allowed us to identify a band at 1639 cm^−1^ (4 → 1 hydrogen‐bonded type II β‐turns), which is characteristic of the silk I conformation. © 2005 Wiley Periodicals, Inc. Biopolymers 78: 249–258, 2005