Determination of the site of disulfide linkage between heavy and light chains of silk fibroin produced by Bombix mori

The analysis of fibroin secretion-deficient 'naked-pupa' mutant silkworms h as suggested that the disulfide linkage between heavy (H) and light (L) cha ins of fibroin, produced by the silkworm, Bombyx mori, is essential in its efficient large-scale secretion from the posterior silk gland cells. Howeve r, the site of disulfide-linkage between H- and L-chains has not been deter mined. In this study, cysteine residues involved in the single disulfide li nkage between H- and L-chains were identified as the twentieth residue from the carboxyl terminus of H-chain (Cys-c20) and CYs-172 of L-chain by seque ncing of genomic clones and peptide analysis. Furthermore, Cys-c4 (fourth r esidue from the carboxyl terminus) and Cys-c1 at the carboxyl terminus of H -chain were shown to form an intramolecular disulfide bond. (C) 1999 Elsevi er Science B.V. All rights reserved.