Adhesive property and mechanism of silkworm egg glue protein

Egg glue proteins (EGPs) are produced by female insects, which can make the eggs firmly attached to the oviposition sites, not affected by wind and rain. Although EGPs are widespread in insects, they have been rarely characterized in molecular detail. Here, the full-length sequence and secondary structure of silkworm EGP is reported. A pentapeptide motif, G-G-N/K/D-Q/E/K-Q/P, was found to repeat 346 times, forming a hydrophilic and elastic β-spiral structure in the silkworm EGP. To reveal the adhesive property and mechanism, we extracted natural EGP from silkworm colleterial gland, and expressed recombinant EGP in Escherichia coli and Pichia pastoris. The glycosylated natural EGP and recombinant EGP from P. pastoris was found to have better adhesive strength than the non-glycosylated recombinant EGP from E. coli. In addition, two transglutaminases in the colleterial gland were found to contribute to the high adhesion of EGP by catalyzing the cross-linking. This study provides important insights into the structure-function relationships associated with this protein, thereby creating new opportunities for the use of insect EGP as a biomaterial. STATEMENT OF SIGNIFICANCE: Egg glue proteins are produced by female insects, which can make the eggs firmly attached to the oviposition sites, not affected by wind and rain. However, genes encoding insect egg glue proteins have not yet been reported, and the molecular mechanism underpinning their adhesion is still unknown. Our study makes a significant contribution to the literature as it identifies the sequence, structure, adhesive property, and mechanism of silkworm egg glue protein. Furthermore, it outlines key insights into the structure-function relationships associated with egg glue proteins. We believe that this paper will be of interest to the readership of your journal as it identifies the first complete sequence of insect egg glue proteins, thereby highlighting their potentials future applications in both the biomedical and technical fields.