ANDY SMITH, assistant professor in biology, presented a paper titled, “Glue or slime: molluscan glue proteins that control gel mechanics,” at the annual meetings of the Society for Integrative and Comparative Biology in New Orleans, La., in January 2004. This talk was co-authored with four IC students: Jan Pawlicki, Laura Pease, Courtney Pierce and Tom Startz.
A wide variety of molluscs secrete adhesive gels that create powerful attachments. The primary structural difference between these gels and the slimy mucus that these molluscs typically secrete is the presence of a few specific proteins. The presence of these proteins in the gel is correlated with at least an order of magnitude increase in adhesive tenacity with minimal change in the overall concentration.
We tested the hypothesis that these proteins control the mechanics of gels. Using gel filtration chromatography, the proteins were isolated from the adhesive mucus of different molluscs. The proteins were then added to different types of large polysaccharides, creating dilute solutions or gels (1-2 percent total organic content). Using a dynamic rheometer, the stiffness and viscosity of these mixtures was compared to identical mixtures that had bovine serum albumen added instead of the adhesive proteins.
The adhesive proteins triggered gelling or visible stiffening of agar, pectin and polygalacturonic acid. The effect was stronger on more negatively charged polymers. The effect also depended on the adhesive proteins’ concentration and structure. Other proteins and carbohydrates from the mucus had no clear mechanical effect on gels.
These findings suggest that the adhesive proteins crosslink large, anionic polymers. Thus, they appear to play a central role in the formation of a glue from a mucus-like secretion. Such a mechanism may be common among invertebrates, and it may guide biomimetic approaches in the development of glues and gels.
Contributed by Nancy Pierce