The exported chaperone Hsp70-x supports virulence functions for Plasmodium falciparum blood stage parasites

Abstract

Malaria is caused by five different Plasmodium spp. in humans each of which modifies the host erythrocyte to survive and replicate. The two main causes of malaria, P. falciparum and P. vivax, differ in their ability to cause severe disease, mainly due to differences in the cytoadhesion of infected erythrocytes (IE) in the microvasculature. Cytoadhesion of P. falciparum in the brain leads to a large number of deaths each year and is a consequence of exported parasite proteins, some of which modify the erythrocyte cytoskeleton while others such as PfEMP1 project onto the erythrocyte surface where they bind to endothelial cells. Here we investigate the effects of knocking out an exported Hsp70-type chaperone termed Hsp70-x that is present in P. falciparum but not P. vivax. Although the growth of Δhsp70-x parasites was unaffected, the export of PfEMP1 cytoadherence proteins was delayed and Δhsp70-x IE had reduced adhesion. The Δhsp70-x IE were also more rigid than wild-type controls indicating changes in the way the parasites modified their host erythrocyte. To investigate the cause of this, transcriptional and translational changes in exported and chaperone proteins were monitored and some changes were observed. We propose that PfHsp70-x is not essential for survival in vitro, but may be required for the efficient export and functioning of some P. falciparum exported proteins.

Cholesterol boundPlasmodium falciparumco-chaperone ‘PFA0660w’ complexes with major virulence factor ‘PfEMP1’ via chaperone ‘PfHsp70-x’

“…Immunofluorescence assays revealed partial co-localization of these GFP-tagged PfHsp40s and PfHsp70-x with PfEMP1, suggesting a role for these chaperones in PfEMP1 transport 30,31 . This was supported by another report where deletion of PfHsp70-x led to delayed export of PfEMP1 to the erythrocyte surface 34 . Another study elucidated the trafficking of PfHsp70x and demonstrated that its export takes place via the PTEX translocon and is directed by an N-terminal secretory signal sequence 35 .…”

The exported chaperone PfHsp70x is dispensable for thePlasmodium falciparumintraerythrocytic lifecycle

“…While this work was under review (and also available on the bioRχiv preprint server), another study was published showing that knockout of PfHsp70x did not affect parasite growth (35). In agreement with these data, our data also demonstrate that PfHsp70x is not required for intraerythrocytic growth, even though PfHsp70x is the only parasite-encoded Hsp70 that is exported to the RBC ( Fig.…”

“…5–8 ). In the case of PfEMP1, the newly published work suggests that knockout of PfHsp70x led to delays in its export and minor loss in cytoadherence, suggesting a role for PfHsp70x in parasite virulence (35). In this case, the data show that PfHsp70x knockout parasites over-express some exported proteins (35).…”

Illuminating how malaria parasites export proteins into host erythrocytes

“…However, what is important to point out is that as no part of the PTEX machinery extends into the host cell (de Koning-Ward et al, 2009;Ho et al, 2018), it is unclear how chaperones in the host cell could dock and retrieve cargo-exiting PTEX to refold and traffic them onto their final destination. The refolding of exported cargo-exiting PTEX and their further trafficking is thought to require exported parasite chaperones or even host HSP70/40 chaperones or the TCP1 ring complex (Batinovic et al, 2017;Charnaud et al, 2017;Jha, Laskar, Dubey, Bhattacharyya, & Bhattacharyya, 2017;Kulzer et al, 2012) However, recently, it was shown that the exported parasite chaperone PfHsp70x was redundant in this process (Cobb et al, 2017), and functional proof for the contribution of other chaperones is still missing.…”