Speaker
Description
Of the five malaria-causing species, Plasmodium falciparum accounts for most malaria-related deaths. Central to the survival and infectivity of the parasite is rapid replication coupled to upregulated protein production. Thus, the development of this malaria parasite is supported by the role of several heat shock proteins (Hsps), which facilitate protein folding. P. falciparum Hsp70-1 (PfHsp70-1) and PfHsp70-z are essential molecular chaperones (molecules that assist proteins to fold correctly) that are cytosol-localized. PfHsp70-z belongs to the Hsp110 cluster of Hsp70-like proteins. Whereas PfHsp70-1 serves as a refolding chaperone, PfHsp70-z is restricted to preventing aggregation of proteins in the cell. The structural features underpinning the functional specialization of these chaperones remain elusive. PfHsp70-z possesses a unique linker segment. In the current study, we explored the role of the linker in regulating the functional specialization of the two P. falciparum Hsp70s. Using recombinant forms of PfHsp70-1, PfHsp70-z, and E. coli Hsp70 (DnaK) as well as their linker switch mutant forms, we explored the effects of the linker mutations using circular dichroism, intrinsic and extrinsic fluorescence coupled to biochemical and in cellulo analyses. Our findings demonstrate that the linker of PfHsp70-z modulates global conformation of the chaperone, regulating several functions such as client protein binding, chaperone, and ATPase activities. In addition, as opposed to the flexible linker of PfHsp70-1, the PfHsp70-z linker is rigid, conferring notable conformational stability to this chaperone, making it an effective holdase chaperone. Our findings highlight the role of the linker in regulating the functional specificity of Hsp70. We discuss the implications of our findings to the development of the malaria parasite at the blood stages of the parasite.
