Fibroin
Fibroin is an insoluble protein created by spiders, the larvae of
Bombyx mori, other moth genera such as
Antheraea,
Cricula,
Samia and
Gonometa, and numerous other insects. Silk in its raw state consists of two main proteins, sericin and
fibroin, fibroin being the structural center of the silk, and sericin being the sticky material surrounding it. Primary structure of fibroin,
n The fibroin protein consists of layers of antiparallel beta sheets. Its primary structure mainly consists of the recurrent amino acid sequence
n. The high glycine content allows for tight packing of the sheets, which contributes to silk's rigid structure and tensile strength. A combination of stiffness and toughness make it a material with applications in several areas, including biomedicine and textile manufacture. Fibroin is known to arrange itself in three structures, called silk I, II, and III. Silk I is the natural form of fibroin, as emitted from the
Bombyx mori silk glands. Silk II refers to the arrangement of fibroin molecules in spun silk, which has greater strength and is often used in various commercial applications.