Bombyx mori silk /3-sheet structure

To characterize the structure of silk, various techniques, namely X-ray diffraction (XRD), vibrational spectroscopy, and cross-polarization magic-angle spinning nuclear magnetic resonance, and so on, have been adopted. Hu et al. reported a study of self-assembled yS-pleated sheets in Bombyx mori silk fibroin films using... 

Silk is produced from the spun threads from silkworms (the larvae of the moth Bombyx mori and related species). The main protein in silk, fibroin, consists of antiparallel pleated sheet structures arranged one on top of the other in numerous layers (1). Since the amino acid side chains in pleated sheets point either straight up or straight down (see p. 68), only compact side chains fit between the layers. In fact, more than 80% of fibroin consists of glycine, alanine, and serine, the three amino acids with the shortest side chains. A typical repetitive amino acid sequence is (Gly-Ala-Gly-Ala-Gly-Ser). The individual pleated sheet layers in fibroin are found to lie alternately 0.35 nm and 0.57 nm apart. In the first case, only glycine residues (R = H) are opposed to one another. The slightly greater distance of 0.57 nm results from repulsion forces between the side chains of alanine and serine residues (2). 

Silk is a fibrous protein produced by several insect species. Commercially, silk is produced from the cocoon stage larvae of the moth caterpillar Bombyx mori, as it has been, in China, for some 4500 years. A single cocoon produces a continuous thread up to 1 km in length, and the protein fibroin contains large amounts of glycine, alanine, tyrosine, proline and serine The peptide chains are arranged in anti-parallel P-sheets which make up the hierarchical structure of the crystalline silk fibres. A number of spiders also produce silk webs, although the fibroin structure is rather different to that from silk worms. 

The silk-like unit characterized by the sequence GAGAGS (G - glycine, A - T. -alanine and S - L-serine) is prevalent in silk fibroin from the silkworm Bombyx mori it assembles into packed antiparallel p-sheet structures stabilized by hydrogen bonding [42]. The elastin-like... 

A detailed structure for Tussah silk fibroin has been derived which is in agreement with the X-ray diffraction data. The structure is similar to that of Bombyx mori fibroin in that it is based on anti-parallel-ohain pleated sheets the method of packing of the sheets, however, is quite different. 

A Bombyx mori silkworm silk thread consists of two triangular water-insoluble silk fibroin fibers glued by water-soluble sericin (see Figure 7.1a). Many views concerning the detailed structure of silk fibers have been published so far. Based on solid-state NMR, Asakura et al. [23-26] reported the structural analysis of natural protein fibers with mixed parallel and antiparallel /6-sheet structures. Alanine tripeptide samples with 100% parallel /6-sheet structure and with 100% antiparallel /6-sheet structure were chosen to characterize the /6-sheet structures following solid-state NMR experiments. AU resonances of the tripeptides were assigned by a comparison of the methyl resonances of Ala3 with different... 

Silks are fibrous protein, some forms of which can be woven into textiles. The best known type of silk have a range of functions, including cocoons of the larvae of the mulberry silkworm. Bombyx mori are reared in captivity [41, 143, 145]. They have repetitive protein sequence [29] with a predominance of alanine, glycine and serine (which is high in silkworm silks but low in spider silks). Silk proteins are comprised of four different structural components (1) elastic [3-spirals, (2) crystalline P-sheets rich in alanine, (3) tight amino acid repeats forming a-helices, and (4) spacer regions [47, 126]. 

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