Crystallization Behavior of Bombyx mori Silkworm Fibroin in Liquid Silk in Static and Flow States: Influence of the Interactions of the Sericin Fractions with the Fibroin

Abstract

The self-assembling behavior of Bombyx mori silkworm fibroin was investigated focusing on the interaction of the two types of silkworm sericin fractions (P, M) with the fibroin in the static and flow states. The dissociation of the sericin M fraction from the fibroin allowed the fibroin to form the silk2 crystal guided by the sericin P fraction still interacting with the fibroin. Water annealing in room temperature water, or the enzymatic hydrolysis caused by the contamination by fibroinase, weakened the interaction between the fibroin and the sericin M fraction. Thus, the interaction of the sericin P fraction with the fibroin was considered to be more stable than that of the sericin M fraction. As a result all of the entities that assembled in the flow state gave almost similar WAXD intensity curves although the coagulation conditions were changed at every trial. The morphology of the entities obtained in the flow state became film-like when a two-dimensional interface was generated between the fibroin and the free sericin molecules. On the other hand, it became fibrous when the fibroin interacted with a new protein fraction (a minor protein fraction that can cause the solution of fibroin into water) instead of the sericin fractions.