Evolutionary Divergence of Lepidopteran and Trichopteran Fibroins

Abstract

Lepidopteran insects produce and secrete silk proteins mainly for cocoon formation. The lepidopteran silks generally consist of several components. Fibroins are a major component of the silks. So far as we know, two different types of fibroins have been described for the silk fiber construction. One is known in the saturniid silkmoth, wherein only one component, fibroin, forms homodimers with a disulfide bond and representing a unit of silk fiber formation (Tamura T, Inoue H, Suzuki Y, Mol Gen Genet 206:189--195, 1987; Tanaka K, Mizuno S, Insect Biochem Mol Biol 31:665--677, 2001). The other mode of fiber construction is the fibroin complex that consists of three components, that is, the fibroin heavy chain (fhc; about 350 kDa), the fibroin light chain (flc; 26 kDa) and P25 (or fibrohexamerin) (about 30 kDa) (Tanaka K, Mori K, Mizuno S, Biochem (Tokyo) 114:1--4, 1993, Tanaka K, Inoue S, Mizuno S, Insect Biochem Mol Biol 29:269--276, 1999a). The representative of this mode is that of Bombyx mori.