A novel bioadhesive protein of silk filaments spun underwater by caddisfly larvae

摘要

Aquatic Larvae of Stenopsychid caddisfly (Stenopsychie marmorata) survive by attaching its catching nets at the bottom of the rocks in the flowing water. It was hypothesized that S. marmorata larva connects small pebbles by producing both silk-like protein and strong adhesive protein simultaneously. A 98 kDa protein（Smap-98k）was identified as an adhesive component by constructing a silk gland –specific cDNA library of S. marmorata. The cDNA sequence of Smap-98k was 2,679 bp long and encoding a 893 amino acids–long open reading frame (ORF) in which the first 19 residues are predict to be the signal peptide. The alignment of the Cys residues indicated the primary structure of this protein to consist of 15 degenerated repeats, each about 50 residues long and contains 6 conserved Cys residues. The Smap-98k was characterized by an abundance of Cys residues and charged amino acids with epidermal growth factor-like (EGF-like) structure. The most common amino acid of this protein was Cys (11.98%), with Pro (9.91%) and Glu (9.26%) following order of magnitude. Cys was assumed to play a role in maintaining the topology of charged amino acids on the molecular surface by intramolecular disulphide-bond formation. The gene was expressed specially in the silk gland similarity to the major silk proteins such like heavy fibroin (H-fibroin) and Light fibroin (L-fibroin) of S. marmorata larvae. The sequence of the protein showed certain homology to the silk-185 kDa of Chironomus pallidivittatus (Midge) which also spin silk underwater. The characterizations of abundance of Cys residues and charged amino acids also shared by Megabalanus rosa cement protein (Mrcp-20k ) and Mytilus galloprovincialis foot protein 2 (Mgfp 2) which both were produced in the marine environment. Although the similarity among Smap-98k, Mrcp-20k and Mgfp 2 sequences were very low, the functional relationship in underwater adhesion of these proteins should be noted.