PubMed:14717703 JSONTXT

{"project":"silkworm","denotations":[{"id":"T1","span":{"begin":110,"end":126},"obj":"Chemical:-"},{"id":"T2","span":{"begin":139,"end":163},"obj":"Chemical:-"},{"id":"T3","span":{"begin":174,"end":188},"obj":"Gene:100146105"},{"id":"T4","span":{"begin":189,"end":192},"obj":"Gene:100146105"},{"id":"T5","span":{"begin":210,"end":221},"obj":"Species:7091"},{"id":"T6","span":{"begin":328,"end":337},"obj":"Chemical:MESH:D004220"},{"id":"T7","span":{"begin":421,"end":435},"obj":"Gene:100146105"},{"id":"T8","span":{"begin":437,"end":440},"obj":"Gene:100146105"},{"id":"T9","span":{"begin":442,"end":445},"obj":"Gene:100146105"},{"id":"T10","span":{"begin":447,"end":450},"obj":"Gene:100146105"},{"id":"T11","span":{"begin":451,"end":454},"obj":"Gene:100146105"},{"id":"T12","span":{"begin":649,"end":652},"obj":"Gene:100146105"},{"id":"T13","span":{"begin":653,"end":656},"obj":"Gene:100146105"},{"id":"T14","span":{"begin":807,"end":810},"obj":"Gene:100146105"},{"id":"T15","span":{"begin":811,"end":814},"obj":"Gene:100146105"},{"id":"T16","span":{"begin":870,"end":873},"obj":"Gene:100146105"},{"id":"T17","span":{"begin":874,"end":877},"obj":"Gene:100146105"},{"id":"T18","span":{"begin":1039,"end":1042},"obj":"Gene:100146105"},{"id":"T19","span":{"begin":1043,"end":1046},"obj":"Gene:100146105"},{"id":"T20","span":{"begin":1085,"end":1088},"obj":"Gene:100146105"},{"id":"T21","span":{"begin":1089,"end":1092},"obj":"Gene:100146105"},{"id":"T22","span":{"begin":1284,"end":1287},"obj":"Gene:100146105"},{"id":"T23","span":{"begin":1288,"end":1291},"obj":"Gene:100146105"},{"id":"T24","span":{"begin":1477,"end":1480},"obj":"Gene:100146105"},{"id":"T25","span":{"begin":1481,"end":1484},"obj":"Gene:100146105"},{"id":"T26","span":{"begin":1527,"end":1530},"obj":"Gene:100146105"},{"id":"T27","span":{"begin":1531,"end":1534},"obj":"Gene:100146105"},{"id":"T28","span":{"begin":1724,"end":1740},"obj":"Chemical:-"},{"id":"T29","span":{"begin":1753,"end":1756},"obj":"Gene:100146105"},{"id":"T30","span":{"begin":1757,"end":1760},"obj":"Gene:100146105"}],"text":"Assembly of the silk fibroin elementary unit in endoplasmic reticulum and a role of L-chain for protection of alpha1,2-mannose residues in N-linked oligosaccharide chains of fibrohexamerin/P25.\nSilk fibroin of Bombyx mori is secreted from the posterior silk gland (PSG) as a 2.3-MDa elementary unit, consisting of six sets of a disulfide-linked heavy chain (H-chain)-light chain (L-chain) heterodimer and one molecule of fibrohexamerin (fhx)/P25. Fhx/P25, a glycoprotein, associates noncovalently with the H-L heterodimers. The elementary unit was found and purified from the endoplasmic reticulum (ER) extract of PSG cells. A substantial amount of fhx/P25 unassembled into the elementary unit was also present in ER. In normal-level fibroin-producing breeds (J-139 and C108), the elementary unit contained fhx/P25 of either 30 kDa (major) or 27 kDa (minor). The 27-kDa fhx/P25 was produced from the 30-kDa form by digestion with the bacterial alpha1,2-mannosidase in vitro. The elementary unit in the ER extract contained only the 30-kDa fhx/P25, whereas both 30- and 27-kDa forms of fhx/P25 were present in the ER plus Golgi mixed extracts. In naked-pupa mutants [Nd(2), Nd-s and Nd-sD], extremely small amounts of fibroin were produced and they consisted of one molecule of 27-kDa fhx/P25 and six molecules of H-chain but no L-chain. When the Nd-sD mutant was subjected to transgenesis with the normal L-chain gene, the (H-L)6fhx1-type elementary unit containing the 30-kDa fhx/P25, was produced. These results suggest that fhx/P25 in the elementary unit is largely protected from digestion with Golgi alpha1,2-mannosidases when L-chains are present in the unit. Models suggesting a role of L-chain for the protection of alpha1,2-mannose residues of fhx/P25 are presented."}