The chromosomal protein Sso7d of the crenarchaeon Sulfolobus solfataricus rescues aggregated proteins in an ATP hydrolysis-dependent manner.

In this work, we show that the nonspecific DNA-bind- ing protein Sso7d from the crenarchaeon Sulfolobus sol- fataricus displays a cation-dependent ATPase activity with a pH optimum around neutrality and a tempera- ture optimum of 70 °C. Measurements of tryptophan flu- orescence and experiments that used 1-anilinonaphtha- lene-8-sulfonic acid as probe demonstrated that ATP hydrolysis induces a conformational change in the mol- ecule and that the binding of the nucleotide triggers the ATP hydrolysis-induced conformation of the protein to return to the native conformation. We found that Sso7d rescues previously aggregated proteins in an ATP hydrol- ysis-dependent manner; the native conformation of Sso7d forms a complex with the aggregates, while the ATP hy- drolysis-induced conformation is incapable of this inter- action. Sso7d is believed to be the first protein isolated from an archaeon capable of rescuing aggregates.