Characteristic 1H Chemical Shifts of Silk Fibroins Determined by 1H CRAMPS NMR

• Published in: Macromolecules Vol. 33; no. 26; pp. 9682 - 9687
• Main Authors: Kimura, Hideaki, Kishi, Satoshi, Shoji, Akira, Sugisawa, Hisashi, Deguchi, Kenzo
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 26.12.2000
• Subjects: Applied sciences; Exact sciences and technology; Natural polymers; Physicochemistry of polymers; Proteins; Insecta; Attacidae; Bombyx mori; NMR spectrometry; Experimental study; Solid state; Silk; Arthropoda; Bombycidae; Lepidoptera; Animal protein; Proton; Fibroin; Antheraea pernyi; Invertebrata; Conformation
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma001167f

CRAMPS NMR of 1H was used for the structural analysis of some natural silk fibroins such as Tussah Antheraea pernyi and Bombyx mori in the solid state. We were able to resolve all expected 1H NMR resonances. When tied to the resolution of 13C NMR via 2D 1H−13C HETCOR experiments, overlapping proton resonance under CRAMPS are able to be further resolved. The simplified 1H signals of these natural proteins could be successfully assigned on the basis of the conformation-dependent 1H chemical shifts of model polypeptides. The 1H chemical shift of the Hα signals of Tussah A. pernyi fibroin adopting an α-helix conformation (4.0 ppm) agrees with that of α-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 1H CRAMPS spectra of B. mori fibroins adopting the silk I or silk II form were similar to those of [Ala-Gly]12 adopting a corresponding conformation. The Hα chemical shifts of the silk I fibroin were 3.9 ppm (singletlike) whereas those of the silk II fibroin exhibited peaks at 5.0 and 3.9 ppm. Further, we found that the 1H chemical shift of side chains in silk I was downfield by 0.4 ppm compared with that in silk II. Thus, it is possible to assign the 1H CRAMPS NMR spectra of natural proteins such as silk fibroins using model polypeptides of known structure as references.