MOLECULAR AND BIOCHEMICAL-COMPARISON OF THE 70-KDA HEAT-SHOCK PROTEINS OF TRYPANOSOMA-CRUZI

An analysis of the genetic organization, regulated expression and bioc hemical properties of the cytoplasmic/nuclear (hsp70) and mitochondria l (mtp70) 70-kDa heat shock proteins of Trypanosoma cruzi is presented . The two proteins are encoded by tandemly arranged gene families that are located on different chromosomes. Both are mildly heat-inducible but have different optimal temperatures for expression. During the swi tch from proliferation to differentiation that occurs during the growt h of T cruzi in culture, the hsp70 level decreases dramatically while the mtp70 level falls only slightly. The subcellular locations of the two proteins differ during heat shock. While mtp70 remains associated with the kinetoplast at all temperatures, hsp70 becomes more concentra ted in the nucleus at higher temperatures. Biochemical analysis of hsp 70 and mtp70 revealed both to be potent ATPases. Each protein binds AT P with a K(m) of about 70 mum and hydrolyzes ATP with a k(cat) of abou t 100 min-1, 100 times greater than the k(cat) of human hsp70. The hig h ATPase activities of hsp70 and mtp70 are further stimulated by incub ation with peptides, suggesting that these trypanosome heat shock prot eins have protein chaperone activity. Finally, mtp70, but not hsp70, w as found to possess autophosphorylation activity in vitro, a property that it shares with prokaryotic hsp70. These findings demonstrate uniq ue cellular and biochemical characteristics of T. cruzi mtp70 and hsp7 0 that suggest that they play distinct physiologic roles in the biolog y of the cell.