Structure Analysis of Bombyx mori Silk Fibroin Using NMR

Abstract

Silks from silkworms and spiders continue to attract attention of researchers in many fields, biochemistry, biophysics, analytical chemistry, polymer chemistry, polymer and textile technologies, and biomaterials. Advances in the most famous silk, Bombyx mori silk fibroin (SF) research, provide many new insights into the structure and dynamics of SF. Here, recent NMR analyses about the structures and dynamics of SF were reviewed. The solution structure of SF stored in the middle silk gland of Bombyx mori silkworm was determined using solution NMR in atomic level. This was type II β-turn structure which was close to random coil but existed in the aggregated states. On the other hand, a new structure of the crystalline regions of the SF fiber after spinning (Silk II) was proposed using several solid- state NMR techniques, and well-known Marsh-Pauling structural model for Silk II was denied partially. The conformational change from SF stored in the middle silk gland to SF fiber was monitored by the change in the fraction of several different conformations determined using ¹³C CP/MAS NMR and discussed in detail on the basis of the primary structure of SF. The hydrations of SF and microscopic interaction with water molecules were also studied by solid state NMR and ²H solution relaxation measurements. Thus, these NMR analyses gave new details relating to the structure and dynamics of SF, which are relevant in light of current interest in the design of man-made new SF and novel SF-based biomaterials.