Andy Smith presented "Sticky, fast-setting glues vs. dried, long-lasting glues: functional differences among gastropod glue proteins" at the annual meeting of the Society for Integrative and Comparative Biology in San Diego this January.
The talk was coauthored with three Ithaca College undergraduates, Sarah Legg '05, Trudy Morrison '05, and Christine Simon '05.
Many molluscs form strong attachments using gel-based glues. These dilute gels are structurally similar to the mucous gels used in locomotion, but they have additional proteins that we have named "glue proteins." The glue proteins have been shown to stiffen gels, apparently by cross-linking anionic polymers.
Different gastropods use their glues for different purposes though. The slug Arion subfuscus releases a defensive secretion that becomes remarkably sticky within seconds. The land snail Helix aspersa produces a glue that dries into a tough film. In both cases, a glue protein is the key structural feature triggering adhesion. Given the difference in function, though, these proteins are likely to have different properties.
We measured the gel-stiffening ability of the glue proteins from both species and their effect on a fluid's ability to wet surfaces. The glue protein from slugs was more effective at low concentrations (~0.2 mg/ml), triggering a two to threefold larger increase in gel stiffness.
The effect of land snail glue proteins increased markedly with concentration, though. At 1 mg/ml, their effect was several fold larger than that of the slug glue proteins. Another difference was that the land snail glue proteins had no significant effect on surface wetting, whereas the slug glue proteins decreased the contact angle of water on wax by 63%.
Based on these results and other structural information, we propose that the glue proteins of slugs are more suited to rapid cross-linking and creation of interfacial adhesion, while the glue proteins of land snails create greater ultimate tensile strength.
Contributed by Nancy Pierce