Characterization of Hip and P23 Toxoplasma gondii Hsp90 co-chaperones

PABLO C. ECHEVERRIA, MARIA J. FIGUERAS, NATALIA DE MIGUEL, MARIANA MATRAJT, JEAN FRANÇOIS DUBREMETZ, SERGIO O. ANGEL

Montana, USA

Congreso; Ninth International Congress on Toxoplasmosis; 2007

Recently, we has been shown that expression and subcellular localization of the T. gondii Hsp90 are developmentally regulated. Geldanamycin, a benzoquinone ansamycin antibiotic capable of binding and disrupting the function of Hsp90, blocked the conversion from the tachyzoite to bradyzoite and from bradyzoite to tachyzoite stages suggesting an important role of this protein in stage interconversion regulation. In higher eukaryotes, Hsp90 is regulated by proteins, the so called co-chaperones, that participate in dynamic multi-chaperone complexes (See schematic model, panel C). Co-chaperones can regulate the ATP hydrolysis of Hsp90, thereby influencing its affinity for client proteins, or can target Hsp90 chaperone to its client protein, or to a particular subcellular compartment. Five proteins were determined to be involved in achieving efficient Hsp90-heterocomplex assembly: Hsp90, Hsp70, Hsp organizing protein (Hop), Hsp90-binding co-chaperone P23 and Hsp40 . Another co-chaperone, the Hsp70 interacting protein (Hip), has also being purified by co-immunoprecipitation (coIP), which was detected in early Hsp90-heterocomplex. By contrast, P23 enters at late stage of the cycle, leading to complete inhibition of the ATPase activity and increasing the apparent affinity of Hsp90 for ATP. Therefore, the roles of p23 as Hsp90 co-chaperone are to lock individual subunits of Hsp90 in an ATP-dependent conformational state that has a high affinity for client proteins, and stabilize the heterocomplex. In order to elucidate the role of Hsp90-heterocomplex during T. gondii differentiation, we cloned and characterized Toxoplasma Hip and P23 proteins, as early and mature Hsp90-hetercomplex markers, respectively.