Tussah Antheraea pernyi

Figure 31 shows the 300 MHz H CRAMPS NMR spectra of three silk fibroins (A) Tussah Antheraea pernyi (a-helix), (B) Bomhyx mori-i (silk I form), and (C) Bomhyx mori- (silk II form) fibroins. They give highly resolved H CRAMPS NMR spectra in the solid state, which are the first high-resolution solid-state H CRAMPS NMR spectra of such natural proteins, as far as we know. The H signals of these fibroins are separated basically into four regions (H , side-chain phenyl, H, and side-chain protons). 

The H nmr spectrum of Tussah Antheraea pernyi fibroin is roughly similar to that of a-helical PLA except for the side-chain phenyl proton signals, as... 

Gly a-helix, b = 84.7 silk I, b = 86.9). The peak intensity of the side-chain protons of Tussah Antheraea pernyi fibroin is higher than that of Bombyx mori, which can be explained in terms of the difference in L-alanine content between them. Thus, it is considered that the side-chain proton signals of the silk fibroins are associated mainly with the methyl protons of the L-alanine residues. Accordingly, we can easily distinguish between Tussah Antheraea pernyi (a-helix) and Bombyx mori-1 fibroins from the peak intensity ratio of against in the H CRAMPS NMR spectra. 

Now it is clear that the H chemical shift reflects the conformation of model polypeptide [Ala-Gly] 12 and natural silk fibroins such as Tussah Antheraea pernyi and Bombyx mori silk fibroins. It is confirmed that the well-defined [Ala-Gly] 12 is a suitable model for the structural study of natural silk fibroins (silk I and silk II forms) using high-resolution solid-state NMR. As a result, the H peak assignment of the silk fibroins on the basis of the conformation-dependent H chemical shifts of model polypeptides can be determined utilizing H CRAMPS NMR and H- C 2D HETCOR NMR, as described in this section. The chemical shift results of model polypeptides [Ala-Gly] 12 synthesized by Shoji et al. play an important role in determining new structures for silk I and silk II forms, as very recently proposed by Lazo and Downing. ... 

Silk fibers are produced by the larvae of specific moth species. There are two major types of silk Tussah silk produced in the wild by Antheraea pernyi and Antheraea mylitta, and Bombyx mori silk, which is produced by cultivated mulberry worms. 

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