Cholesterol bound Plasmodium falciparum co-chaperone \u2018PFA0660w\u2019 complexes with major virulence factor \u2018PfEMP1\u2019 via chaperone \u2018PfHsp70-x\u2019

Ankita Behl,Prakash Chandra Mishra,Vikash Kumar,Rachna Hora,Jiban J Panda,Anjali Bisht

doi:10.1038/s41598-019-39217-y

Abstract

Lethality of Plasmodium falciparum caused malaria results from ‘cytoadherence’, which is mainly effected by exported Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family. Several exported P. falciparum 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 interacts with cholesterol bound 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’. These findings further the understanding of PfEMP1 export in malaria parasites, though their in vivo validation remains to be performed.

Highlights

P. falciparum is the major cause of severe complicated malaria that is responsible for ~0.4 million deaths annually[1]
Parasite encoded exported chaperones are involved in the cellular refurbishment of infected human erythrocytes, and play an important role in the establishment of protein folding pathways in the host cell
We have explored various aspects of PFA0660w-PfHsp70-x interaction, and attempted to delineate its function in infected red blood cells

Summary

Introduction

P. falciparum is the major cause of severe complicated malaria that is responsible for ~0.4 million deaths annually[1] This high mortality rate results from the ability of infected red blood cells (iRBCs) to bind host endothelial receptors by the process of cytoadherence, which is largely due to the PfEMP1 family of proteins[2,3]. PfEMP1 is one of the several exported protein families of P. falciparum that play a crucial role in host erythrocyte remodelling to facilitate virulence, growth and survival of the parasites[4]. Members of the Hsp[40] category of chaperones are classified into four types (I to IV)[17], of which several are believed to be exported These members of the ‘malaria exportome’[5] play crucial roles in cellular processes like protein translation, folding, translocation, and degradation[17], underscoring their importance in parasite biology. Our results provide mechanistic insights into the functional role of the PFA0660w-PfHsp70-x chaperone pair and serve to fill the key knowledge gaps in the understanding of P. falciparum biology

Methods

Results

Conclusion