Abstract
Terrestrial organisms have systems to escape from desiccation stresses. For example, tardigrades (also known as water bears) can survive severe dried and other extreme environments by anhydrobiosis. Although their extraordinary ability has enchanted people, little is known about the detailed molecular mechanisms of anhydrobiosis. Here, we focused on the tardigrade Ramazzottius varieornatus, one of the toughest animals on Earth. A transcriptome database of R. varieornatus shows that genes encoding a Ferritin-like protein are upregulated during desiccation or ultraviolet radiation. This protein shows sequence similarity to enigmatic proteins in desiccation-tolerant bacteria and plants, which are hypothesized to be desiccation-related. However, because these proteins lack detailed biological information, their functions are relatively unknown. We determined an atomic (1.05 Å) resolution crystal structure of a Ferritin-like protein from R. varieornatus. The structure revealed a dinuclear metal binding site, and we showed that this Ferritin-like protein has phosphatase activity toward several metabolite compounds including unusual nucleotide phosphates produced by oxidative or radiation damage. We also found that a homologous protein from a desiccation- and ultraviolet-tolerant bacterium Deinococcus radiodurans is a metabolite phosphatase. Our results indicate that through cleaning up damaged metabolites or regulation of metabolite levels, this phosphatase family can contribute to stress tolerances. This study provides a clue to one of the universal molecular bases of desiccation-stress tolerance.