Comparative characterisation of Plasmodium falciparum Hsp70-1 relative to E. coli DnaK reveals functional specificity of the parasite chaperone

Abstract

Hsp70 is one of the most prominent molecular chaperones. Although Hsp70s from various organisms are generally conserved, they exhibit specialised cellular functions. It remains to be fully understood how these highly conserved molecules exhibit specialised functional features. Plasmodium falciparum Hsp70-1 (PfHsp70-1) is a cytosol localised molecular chaperone that is implicated in the cyto-protection and pathogenicity of the malaria parasite. In the current study, we investigated the comparative structure-function features of PfHsp70-1 relative to its homologue, E. coli Hsp70 (DnaK) and a chimeric protein, KPf, that was constituted by the ATPase domain of DnaK and the substrate binding domain (SBD) of PfHsp70-1. Recombinant forms of all the three Hsp70s exhibited similar secondary and tertiary structural fold. We further established that compared to DnaK, both KPf and PfHsp70-1 were more stable to heat stress and exhibited higher basal ATPase activity. A recombinant P. falciparum Hsp40 (PfHsp40) stimulated the ATPase activities of all the three Hsp70s. In addition, both PfHsp70-1 and KPf exhibited preference for asparagine rich peptides as opposed to DnaK. Furthermore, all the three proteins exhibited self-association capabilities in vitro. Recombinant P. falciparum adenosylmethionine decarboxylase (PfAdoMetDC) co-expressed in E. coli with either KPf or PfHsp70-1 was produced as a fully folded product. On the other hand, co-expression of PfAdoMetDC with heterologous DnaK in E. coli did not promote folding of the former. These findings demonstrated that the SBD of PfHsp70-1 regulates several functional features of the protein and that this molecular chaperone is tailored to facilitate folding of plasmodial proteins.