It has a serine and threonine phosphatase activity. Has a specialized role in the heat shock response. May be responsible for the dephosphorylation of hsp90. Also has a role in maintaining osmotic stability. H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Binds 2 magnesium or manganese ions per subunit. Monomer. Belongs to the PP2C family.