Cholesterol bound Plasmodium falciparum co-chaperone ‘PFA0660w’ complexes with major virulence factor ‘PfEMP1’ via chaperone ‘PfHsp70-x’

Abstract

Lethality of Plasmodium falciparum (Pf) caused malaria results from cytoadherence, which is effected by exported Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family. Several exported Pf proteins (exportome) including chaperones alongside cholesterol rich microdomains are crucial for PfEMP1 translocation to infected erythrocyte surface. An exported Hsp40 (heat shock protein 40) PFA0660w functions as a co-chaperone of PfHsp70-x, and these co-localize to specialized intracellular mobile structures termed J-dots. Our studies attempt to understand the function of PFA0660w-PfHsp70-x chaperone pair using recombinant proteins. Biochemical assays reveal that N and C-terminal domains of PFA0660w and PfHsp70-x respectively are critical for their activity. We show the novel direct interaction of PfHsp70-x with the cytoplasmic tail of PfEMP1, and binding of PFA0660w with cholesterol. PFA0660w operates both as a chaperone and lipid binding molecule via its separate substrate and cholesterol binding sites. PfHsp70-x binds cholesterol linked PFA0660w and PfEMP1 simultaneously in vitro to form a complex. Collectively, our results and the past literature support the hypothesis that PFA0660w-PfHsp70-x chaperone pair assists PfEMP1 transport across the host erythrocyte through cholesterol containing J-dots. Since PFA0660w seems essential for parasite survival, characterization of its interaction with PfHsp70-x and J-dots may form the basis for development of future antimalarials.