The silk fibroin heavy chain protein has a molecular weight of about 380 kDa and contains 5263 amino acids. Glycine is the most abundant amino acid in heavy chain proteins, accounting for about 45% of the total. In addition to glycine, alanine, serine and tyrosine also accounted for a high proportion, accounting for roughly 29%, 10% and 7%, respectively, and these four amino acids accounted for more than 90% of the total. Heavy chain proteins have a relatively single amino acid composition and a large number of repeat regions. The silk fibroin heavy chain gene is located on chromosome 25. It is about 17 kb in length and contains two exons of 67 bp and 15750 bp, respectively. The repeat region of the silk fibroin heavy chain is located on the second exon.

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The silk fibroin light chain protein has a molecular weight of approximately 25 kDa and contains 262 amino acids. Alanine and aspartic acid are the most abundant amino acids in light chain proteins, both accounting for about 15% of the total, while glycine accounts for only about 10%. The proportion of amino acids such as hydrophobic amino acids such as isoleucine, leucine and valine was significantly higher in phase than in streptin, all accounting for about 7%. The composition of amino acids of phase specific streptavids and light chain proteins is more diverse. The silk fibroin light chain gene is located on chromosome 14 and is approximately 13.5 kb in length, containing seven exons and six introns. The light chain protein contains three cysteine residues, amino acids 83, 142, and 172, and these two cysteine residues form intramolecular disulfide bonds.

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