Conservation of Silk Genes in Trichoptera and Lepidoptera

Abstract

Larvae of the sister orders Trichoptera and Lepidoptera are characterized by silk secretion from a pair of labial glands. In both orders the silk filament consists of heavy (H)-and light (L)-chain fibroins and in Lepidoptera it also includes a P25 glycoprotein. The L-fibroin and H-fibroin genes of Rhyacophila obliterata and Hydropsyche angustipennis caddisflies have exon/intron structuring (seven exons in L-fibroin and two in H-fibroin) similar to that in their counterparts in Lepidoptera. Fibroin cDNAs are also known in Limnephilus decipiens, representing the third caddisfly suborder. Amino acid sequences of deduced L-fibroin proteins and of the terminal H-fibroin regions are about 50% identical among the three caddisfly species but their similarity to lepidopteran fibroins is \25%. Positions of some residues are conserved, including cysteines that were shown to link the L-fibroin and H-fibroin by a disulfide bridge in Lepidoptera. The long internal part of H-fibroins is composed of short motifs arranged in speciesspecific repeats. They are extremely uniform in R. obliterata. Motifs (SX) n , GGX, and GPGXX occur in both Trichoptera and Lepidoptera. The trichopteran H-fibroins further contain charged amphiphilic motifs but lack the strings of alanines or alanine-glycine dipeptides that are typical lepidopteran motifs. On the other hand, sequences composed of a motif similar to ERIVAPTVITR surrounded by the (SX) 4-6 strings and modifications of the GRRGWGRRG motif occur in Trichoptera and not in Lepidoptera.

Characterization of a Cysteine-Rich Protein Specifically Expressed in the Silk Gland of CaddisflyStenopsyche marmorata(Trichoptera; Stenopsychidae)

“…Heavy-chain fibroin (H-fibroin) and light-chain fibroin (L-fibroin), the major components of the lepidopteron filament, have been found to be conserved in caddisfly by a screen of silk gland specific cDNA libraries. 2,3) Compared to Lepidoptera, the H-fibroin of caddisfly has a higher molecular mass (>400 kDa), is rich in charged amino acids, and is predominantly hydrophilic. On the other hand, the L-fibroins of the caddisfly and Lepidoptera are similar in terms of their sizes, hydrophobicity, and content of charged residues.…”

Applicability of biotechnologically produced insect silks

“…Upon acidification, the side chains are protonated and enable the formation of homodimers. The importance of this mechanism is further underlined by the finding that the residues involved in the inhibition of premature dimer formation are conserved in Lepidoptera and Trichoptera [31,32]. In general, silk processing in silk glands of spiders shows similarities to the process in silkworms.…”

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

“…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.…”