Epiphragmin, the major protein of epiphragm mucus from the vineyard snail, Cernuella virgata

The organic fraction of epiphragm mucus from the snail Cernuella virgata (Mollusca: Helicidae) consists predominantly of protein (17–23 dry wt.%) rather than carbohydrate (≤ 0.4–2.0 dry wt.%), and the former underpins epiphragm membrane structure. The major protein (‘epiphragmin’) has an apparent molecular mass of ∼ 86 kDa and is encoded by a cDNA (Genbank accession EF602752) which specifies a secreted protein of 81.2 kDa. The central region of the epiphragmin polypeptide is a coiled coil-forming region which is homologous to part of AglZ, a bacterial filament-forming protein. Coiled coil-driven self-assembly of epiphragmin probably underpins the formation of sheets in epiphragm membranes and the ability of epiphragm mucus to serve as an adhesive. The C-terminal region of epiphragmin is a fibrinogen-related domain (FReD) that is homologous to the fibrinogen-related proteins (FREPs) found in the hemolymph of freshwater snails. The material properties of epiphragm membranes resemble those of bovine ligament elastin. Wooden lap-joints bonded by rehydrated epiphragm fragments developed dry shear strength values of 1.4 ± 0.1 MPa.