A Potentially Versatile Nucleotide Hydrolysis Activity of Group II Chaperonin Monomers from Thermoplasma acidophilum.

Compared to the group I chaperonins such as Escherichia coli GroEL, which facilitate protein folding, many aspects of the functional mechanism of archaeal group 11 chaperonins are still unclear. Here, we show Ihat monomeric forms of archaeal group II chaperonin aand fi from Thermoplasma acidophilum maybe purified stabl2y and that these monomers display a strong AMPase activity in the presence of divalent ions, especially Co2+ ion, in addition to ATPase and ADPase activities. Furthermore, other nucleoside phosphates (guanosine, cytidine, uridine, and inosin phosphates) in addition to adenine nucleotides were hydrolyzed. From analyses of the products of hydrolysis using HPLC, it was revealed that the monomeric chaperonin successively hydrolyzed the phosphoanhydride and phosphoester bonds of ATP in the order of y to a. This activity was strongly suppressed by point mutation of specific essential aspartic acid residues. Although these archaeal monomeric chaperonins did not alter the refolding of MDH, their novel versatile nucleotide hydrolysis activity might fulfill a new function. Western blot experiments demonstrated that the monomeric chaperonin subunits were also present in lysed cell extracts of T. acidophilum, and partially purified native monomer displayed Co2+-dependent AMPase activity. [ABSTRACT FROM AUTHOR]