This family consists of several moth fibroin light chain (L-fibroin) proteins. Fibroin of the silkworm, Bombyx mori, is secreted into the lumen of posterior silk gland (PSG) from the surrounding PSG cells as a molecular complex consisting of a heavy (H)-chain of approximately 350 kDa, a light (L)-chain of 25 kDa and a P25 of about 27 kDa. The H- and L-chains are disulfide-linked but P25 is associated with the H-L complex by non-covalent force [1].

1: Determination of the site of disulfide linkage between heavy and light chains of silk fibroin produced by Bombyx mori. Tanaka K, Kajiyama N, Ishikura K, Waga S, Kikuchi A, Ohtomo K, Takagi T, Mizuno S; Biochim Biophys Acta 1999;1432:92-103. PMID:10366732