Tardigrades are a group of small invertebrates that can tolerate extreme deprivation of water (desiccation). While tardigrades produce certain intrinsically disordered proteins and sugars to act as excipients and aid protein recovery from desiccation, we hypothesize that their other proteins have also evolved to withstand desiccation. We assembled an alignment of 30 tardigrade adenylate kinase (ADK) sequences, analyzed their phylogeny and constructed ancestral sequences. We found some conserved features of tardigrade ADKs that are not observed in the ADKs of other closely related species: a 30-aa long N-terminal insertion, an internal disulfide bridge, and altered surface chemistry. We expressed and purified a subset of extant tardigrade ADKs and compared their catalytic ability with E. coli ADK, with future plans to investigate their recovery from desiccation and their interactions with excipients in the desiccated state.
Gu et al. (Sun,) studied this question.