For water bears, the glass is all full

SAN DIEGO — Water bears turn into glass when they dry out.

That glazing enables the hardy microscopic creatures, also known as tardigrades, to withstand extreme desiccation, biologist Thomas Boothby of the University of North Carolina at Chapel Hill reported December 15 at the annual meeting of the American Society for Cell Biology.

Boothby and colleagues discovered that water bears make a lot of certain proteins in dry conditions. Those proteins are floppy and unformed when tardigrades are hydrated. As the animals dry, the proteins fold into a glasslike solid that encases and protects other proteins and molecules that would normally fall apart when dried. Adding water melts the glass and the tardigrade recovers. Yeast engineered to produce the tardigrade glass proteins survive desiccation better than they normally do, Boothby’s collaborators discovered.

Reducing levels of the glass proteins hampers the water bears’ desiccation resistance, but doesn’t harm their remarkable ability to withstand extreme cold. That suggests that other proteins offer cold protection, Boothby said.

Tardigrade glass may have practical uses, such as preserving useful proteins in a dry state, experiments with an enzyme called lactate dehydrogenase suggest. The enzyme loses its activity when dried out. But when the researchers mixed the enzyme with the glass proteins before drying, the enzyme bounced back to normal activity when rehydrated. Mixing in water bear proteins after drying didn’t help, indicating that the glass proteins need to encase other molecules to protect them.

Glass proteins may one day help preserve vaccines in parts of the world where keeping them cold is impractical, Boothby suggested.