Key words: STI-1 -Hop -HSP70 -stress response -Trypanosoma cruziThe stress-induced protein-1 (STI-1), also known as Hop (HSP70/HSP90-organising protein), is a co-chaperone that interacts with the heat-shock proteins HSP70 and HSP90 (Smith et al. 1993). This multi-chaperone complex is required for steroid receptor (SR) assembly (Chen et al. 1996, Dittmar et al. 1996, Chang et al. 1997 in which STI-1 acts as a mediator, potentially increasing the rate of SR maturation (Morishima et al. 2000). Furthermore, this chaperone complex is able to reconstitute hepadnavirus reverse transcriptase activity in vitro (Hu et al. 2002), suggesting that a purified assembly system could be used to mediate various biological processes requiring HSP90 function (Pratt & Toft 2003).STI-1 acts as an adaptor protein, mediating the interaction between HSP70 and HSP90 through its tetratricopeptide repeat (TPR) domains. The N-terminal TPR domain (TPR1) specifically recognizes the C-terminus of HSP70, whereas the central TPR domain (TPR2A) binds the C-terminus of HSP90 (Chen & Smith 1998, Scheufler et al. 2000. The C-terminal domain of STI-1 seems to be involved in the interactions with both HSPs (Flom et al. 2007, Onuoha et al. 2008. STI-1 may also modulate HSP activities (Johnson et al. 1998, Richter et al. 2003, Odunuga et al. 2004). The STI-1 gene was first isolated and characterized in Saccharomyces cerevisiae during a genetic screen for proteins involved in the heat-shock response. The gene was named "stress-inducible" because, like other wellcharacterized HSP genes, it was induced by heat shock and by the arginine analogue canavanine. However, the nucleotide sequence of STI-1 displayed no similarity to the sequences of other HSP-encoding genes (Nicolet & Craig 1989). Like their counterpart in yeast, the mouse and Caenorhabditis elegans STI-1 homologues are induced by heat shock (Lässle et al. 1997, Song et al. 2009). Interestingly, a soybean homologue has been shown to be induced by either heat or cold stress (Zhang et al. 2003). In addition, the upregulation of STI-1 observed in human SV-40-transformed fibroblasts or mouse macrophages exposed to bacterial lipopolysaccharide demonstrates that stress conditions unrelated to temperature may also lead to the induction of STI-1 expression (Honoré et al. 1992, Heine et al. 1999. The murine STI-1 was identified as a cytoplasmic protein (Lässle et al. 1997). However, a small fraction of STI-1 was found bound to a cellular prion protein at the cell membrane, where it promotes neuroprotection against cell death (Zanata et al. 2002). Moreover, STI-1 accumulates in the nucleus of murine fibroblasts after treatment with leptomycin B, a nuclear export inhibitor . A human homologue has also been found in the Golgi apparatus and in small vesicles within fibroblasts (Honoré et al. 1992).A protozoan orthologue of STI-1 has been characterized in Leishmania major and shown to be upregulated when the parasites are exposed to heat stress conditions (Webb et al. 1997). This parasite, like other trypanoso-S...