Raman study of poly(alanine-glycine)-based peptides containing tyrosine, valine, and serine as model for the semicrystalline domains of Bombyx mori silk fibroin
✍ Scribed by Paola Taddei; Tetsuo Asakura; Juming Yao; Patrizia Monti
- Book ID
- 101719291
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 2004
- Tongue
- English
- Weight
- 378 KB
- Volume
- 75
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Abstract
For a deeper insight into the structure of Bombyx mori silk fibroin, some model peptides containing tyrosine (Y), valine (V), and serine (S) in the basic (AG)~n~ sequence were synthesized by the solid‐phase method and analyzed by Raman spectroscopy in order to clarify their conformation and to evaluate the formation and/or disruption of the ordered structure typical of B. mori silk fibroin upon incorporation of Y, V, and S residues into the basic (AG)~n~ sequence. The Raman results indicated that the silk I structure remains stable only when the Y residue is positioned near the chain terminus; otherwise, a silk I → silk II conformational transition occurs. The peptides AGVGAGYGAGVGAGYGAGVGAGYG(AG)~3~ and (AG)~3~YG(AG)~2~VGYG(AG)~3~YG(AG)~3~ treated with LiBr revealed a prevalent silk II conformation; moreover, the former contained a higher amount of random coil than the latter. This result was explained in relation to the different degrees of interruption of the (AG)~n~ sequence. The Raman analysis of the AGSGAG‐containing samples confirmed that the AGSGAG hexapeptide is a good model for the silk II crystalline domain. As the number of AGSGAG repeating units decreased, the random coil content increased. The study of the Y domain (I~850~/I~830~ intensity ratio) allowed us to hypothesize that in the packing characteristic of Silk I and Silk II conformations the Y residues experience different environments and hydrogen‐bonding arrangements; the packing typical of silk I structure traps the tyrosyl side chains in environments more unfavorable to phenoxyl hydrogen‐bonding interactions. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004