title: Protein composition of silk filaments spun under water by caddisfly larvae.
abstract: Silk fiber produced by the larvae of Trichoptera (caddisflies) and Lepidoptera (moths and butterflies) is composed of two filaments embedded in a layer of glue proteins. In an aerial environment Lepidoptera spin silk filaments assembled from heavy chain fibroin (H-fibroin), light chain fibroin (L-fibroin), and the glycoprotein P25. The silk filament of caddisflies, which is produced and persists in water, contained homologues of H-fibroin (>500 kDa) and L-fibroin (25 kDa) but not of P25. The amphiphilic nature of H-fibroin and its high content of charged amino acids probably facilitate the secretion and storage of a covalently linked L-fibroin/H-fibroin dimer in the absence of P25. Several types of short amino acid motifs were arranged in orderly fashion in the regularly reiterated repeats that made up more than 95% of the length of H-fibroin. The H-fibroins of Hydropsyche angustipennis and Limnephilus decipiens from different caddisfly suborders contained GPXGX, SXSXSXSX, and GGX motifs such as the lepidopteran and spider silks but differed from them by a lack of poly(A) and poly(GA) motifs. H-fibroins of both caddisfly species harbored a conserved repeat of 31 residues but were distinguished by a few species-specific motifs and their organization in higher order repeats. Structural differences may be related to the silk function as a catching net in H. angustipennis and a stitching fiber in L. decipiens.
authors.affiliation: Biology Centre, Academy of Sciences, Institute of Entomology, Branisovská 31, 370 05 & Ceské Budejovice, Czech Republic.
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Yonemura
authors.forename: Frantisek
authors.initials: F
authors.lastname: Sehnal
authors.forename: Kazuei
authors.initials: K
authors.lastname: Mita
authors.forename: Toshiki
authors.initials: T
authors.lastname: Tamura
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017124:Conserved Sequence; D018076:DNA, Complementary / Q000235:genetics; D005349:Fibroins / Q000737:chemistry / Q000235:genetics; D005786:Gene Expression Regulation; D007313:Insecta / Q000235:genetics*; D007814:Larva / Q000502:physiology*; D007915:Lepidoptera / Q000235:genetics*; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D047011:Silk / Q000235:genetics* / Q000302:isolation & purification / Q000648:ultrastructure*
chemical_list: D018076:DNA, Complementary; D047011:Silk; D005349:Fibroins