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.

Nanomechanics of new materials — AFM and computer modelling studies of trichoptera silk

“…Individual fibers of caddisfly silk can be a couple of centimeters long and 0 5 − 7 micrometers wide, with a rather uniform height of 0 8 − 1 0 micrometers. Ribbons are composed of bundles of 15 − 25 Å filaments of H-fibroin and L-fibroin [8,9]. Additionally, both ribbons are embedded in the peripheral layer which is rich in oligosaccharides [8].…”

Molecular cloning, gene expression analysis, and recombinant protein expression of novel silk proteins from larvae of a retreat-maker caddisfly, Stenopsyche marmorata

“…In the domestic silkworm Bombyx mori, H-fibroin and L-fibroin form a complex by a disulfide linkage between Cys-c20 of H-fibroin and Cys-172 of L-fibroin [15]. Amino acid sequences of H-fibroin and L-fibroin from B. mori around these regions were homologous to H-fibroin and L-fibroin from caddisflies, H. angustipennis and L. decipiens [13], and also to Smsp-1 and Smsp-3 from S.…”

“…S6A), we tried cDNA cloning of L-fibroin from S. marmorata using the sequence alignment information of L-fibroin from other caddisflies. We designed another degenerate primer, Smsp-3-RV1 (Table S1), based on the highly homologous sequence region "NN(V/I)GAAATSAAT" found in the sequence alignment of L-fibroin from three caddisfly species, Limnephilus decipiens, Rhyacophila obliterate, and Hydropsyche angustipennis [13,14] (Fig. S6B).…”

“…In the present study, we successfully performed cDNA cloning, gene expression analysis, angustipennis, BAF62094 [13]; Hesperophylax occidentalis, AIO11229 [17]; Limnephilus decipiens, BAF62096 [13]; Rhyacophila obliterate, BAH80180 [14].…”

“…The proteins were stained by the reverse staining method [7] for the subsequent mass spectrometry analysis. [13,14] and the N-terminal amino-acid sequence of Smsp-3 from Stenopsyche marmorata. The highly homologous sequence region, used for design of the degenerate primer, Smsp-3-RV1, is surround with red broken lines.…”