83-KILODALTON HEAT-SHOCK PROTEINS OF TRYPANOSOMES ARE POTENT PEPTIDE-STIMULATED ATPASES

A Crithidia fasciculata 83-kDa protein purified during a separate study of C. fasciculata trypanothione synthetase was shown to have ATPase activity and to belong to the hsp90 family of stress proteins. Because no ATPase activity has previously been reported for the hsp90 class, ATP utilization by C fasciculata hsp83 was characterized: this hsp83 has an ATPase k(cat) of 150 min-1 and a K(m) of 60-mu-M, whereas the homologous mammalian hsp90 binds ATP but has no ATPase activity. Crithidia fasciculata hsp83 undergoes autophosphorylation on serine and threonine at a rate constant of 3.3 x 10(-3) min-1. Similar analysis was performed on recombinant Trypanosoma cruzi hsp83, and comparable ATPase parameters were obtained (k(cat) = 100 min-1, K(m) = 80-mu-M, k(autophosphorylation) = 6.3 x 10(-3) min-1). The phosphoenzyme is neither on the ATPase hydrolytic pathway nor does it affect ATPase catalytic efficiency. Both C. fasciculata and T. cruzi hsp83 show up to fivefold stimulation of ATPase activity by peptides of 6-24 amino acids.