Fibroina

Fibroina, or fibroin in English, is a fibrous protein that forms the structural core of silk fibers produced by certain arthropods, most notably the domesticated silkworm Bombyx mori. It is secreted by specialized silk glands and, after spinning, becomes the main load-bearing component of the silk filament, which is typically coated with sericin, a gummy protein that initially cements the fibers.

Molecular structure and composition: Silk fibroin is a high-molecular-weight protein that exists as a complex of heavy and light chain polypeptides linked by disulfide bonds, functioning together with a small glycoprotein component. The heavy chain contains repetitive amino acid motifs rich in glycine and alanine, such as glycine-alanine repeats, which promotes the formation of beta-sheet crystalline regions. These crystalline domains intermingle with amorphous regions, yielding a protein that is strong yet flexible.

Biosynthesis and assembly: In silkworms, fibroin is produced in the posterior silk gland and assembled into a solution that is secreted into the silk duct. During spinning, the fibroin molecules align and crystallize into beta-sheet-rich fibers, producing a material with high tensile strength and toughness. The sericin coating that accompanies raw silk is later removed for many applications.

Properties and applications: Silk fibroin’s combination of strength, elasticity, and biocompatibility makes it valuable in textiles and as a biomaterial. It is studied for sutures, tissue engineering scaffolds, drug delivery systems, and various biomedical devices. Research continues into recombinant production and modification of fibroin to tailor its mechanical and degradation properties.