Characteristic H-1 chemical shifts of silk fibroins determined by H-1 CRAMPS NMR

CRAMPS NMR of H-1 was used for the structural analysis of some natural silk fibroins such as Tussah Antheraea pernyi and Bombyx mori in the solid stat e. We were able to resolve all expected H-1 NMR resonances. When tied to th e resolution of C-13 NMR via 2D H-1-C-13 HETCOR experiments, overlapping pr oton resonance under CRAMPS are able to be further resolved. The simplified H-1 signals of these natural proteins could be successfully assigned on th e basis of the conformation-dependent H-1 chemical shifts of model polypept ides. The H-1 chemical shift of the H-alpha signals of Tussah A. pernyi fib roin adopting an alpha -helix conformation (4.0 ppm) agrees with that of al pha -helical poly(L-alanine) (3.9 ppm) to within +/-0.1 ppm. A well-defined poly(L-alanylglycine), [Ala-Gly](12), was used as a model polypeptide of B . mori silk fibroin. The H-1 CRAMPS spectra of B. mori fibroins adopting th e silk I or silk II form were similar to those of [Ala-Gly](12) adopting a corresponding conformation. The H-alpha chemical shifts of the silk I fibro in were 3.9 ppm (singletlike) whereas those of the silk II fibroin exhibite d peaks at 5.0 and 3.9 ppm. Further, we found that the H-1 chemical shift o f side chains in silk I was downfield by 0.4 ppm compared with that in silk II. Thus, it is possible to assign the H-1 CRAMPS NMR spectra of natural p roteins such as silk fibroins using model polypeptides of known structure a s references.