Although this structure is novel to materials scientists, it’s old hat to evolution. A similar protein called a toll-like receptor is part of an ancient immune system feature found across plants, invertebrates and vertebrates. These receptors sit on the surface of immune cells, binding tightly to pieces of invading microbes and releasing them later. Harrington and his team suggest the horseshoe-shaped protein may use a similar “host-guest” dynamic to grab onto other proteins in the slime, binding strongly but reversibly to form the powerful fibers. Those are magic words to materials scientists working on developing replacements for plastic that can be broken down easily and re-formed into new shapes.
These horseshoe proteins are a significant find, says Yendry Corrales Ureña, a researcher at Costa Rica’s National Laboratory of Nanotechnology who studies velvet worm slime but wasn’t involved in the study. She adds, however, that these proteins don’t account for important properties of the slime such as its toughness or elasticity. “They are just one piece of the larger puzzle.”
Julian Monge Najera, an ecologist at the University of Costa Rica who researches invertebrate evolution, says the fact that three velvet worm species from different continents have the same protein shape in their slime underscores how incredibly ancient velvet worms are and how long ago their chemical R&D must have occurred.
The fossil record shows that velvet worms have existed almost exactly as they do now for at least 300 million years, predating both dinosaurs and today’s continents. “If I could go back in a time machine, the velvet worms I would catch in the post-Cambrian period would be identical to the ones in Costa Rica’s cloud forests today,” Monge Najera says—phase-shifting slime and all.
Harrington and his team are working to purify the horseshoe protein from the slime and confirm its structure via electron microscopy. “We won’t be milking velvet worms for slime to replace plastics,” Harrington says. “But we hope to copy their chemical tricks.” {read}