Plasmodium falciparum-encoded exported hsp70/hsp40 chaperone/co-chaperone complexes within the host erythrocyte

Abstract

SummaryMalaria parasites modify their host cell, the mature human erythrocyte. We are interested in the molecules mediating these processes, and have recently described a family of parasite-encoded heat shock proteins (PfHsp40s) that are targeted to the host cell, and implicated in host cell modification. Hsp40s generally function as co-chaperones of members of the Hsp70 family, and until now it was thought that human Hsp70 acts as the PfHsp40 interaction partner within the host cell. Here we revise this hypothesis, and identify and characterize an exported parasite-encoded Hsp70, referred to as PfHsp70-x. PfHsp70-x is exported to the host erythrocyte where it forms a complex with PfHsp40s in structures known as J-dots, and is closely associated with PfEMP1. Interestingly, Hsp70-x is encoded only by parasite species that export the major virulence factor EMP1, implying a possible role for Hsp70-x in EMP1 presentation at the surface of the infected erythrocyte. Our data strongly support the presence of parasite-encoded chaperone/co-chaperone complexes within the host erythrocyte, which are involved in protein traffic through the host cell. The host-pathogen interaction within the infected erythrocyte is more complex than previously thought, and is driven not only by parasite co-chaperones, but also by the parasite-encoded chaperone Hsp70-x itself.

Export of virulence proteins by malaria-infected erythrocytes involves remodeling of host actin cytoskeleton

“…These structures were evident in absence of PfPTP1 and therefore its function is not required for their formation. They may be related vesicular structures called J-dots observed in the cytosol of parasite-infected RBCs 37 and the partial colocalization of PfPTP1 with PfHsp70-x supports this notion. J-dots may be chaperone complex transport vehicles and their membrane characteristics are different from MC.…”

“…To determine whether PfPTP1 was localized to transport vesicles within the RBC cytoplasm, we performed colocalization studies with PfPTP2, a marker for EDVs 38 and PfHsp70-x, which is associated with J-dots. 37 PfPTP1 did not overlap with PfPTP2 indicating it was not localized to EDVs ( Figure 2D). In some instances, EDVs were closely associated with PfPTP1-labeled MC confirming a connection between these structures in transport processes.…”

“…Cells were labeled with antibodies: a-PTP1 (1:500), a-SBP1 (1:500), a-REX1 (1:2000), 32 a-GFP (1:500), a-HA (1:100), a-MAHRP1 (1:100), 33 a-Pf332 (1:500), 34 a-STEVOR (1:500), 35 a-Rif29 (1:200), 36 a-Hsp70-x (1:200), 37 a-PTP2 (1:250). 38 Cells were viewed with a Zeiss Plan-Apochromat 1003/1.4 numeric aperture oil-immersion lens on a Zeiss Axioskop 2 microscope equipped with a PCO SensiCam (12-bit) camera.…”

Maurer's clefts, the enigma of Plasmodium falciparum

“…Additionaly, there is no known vesicular transport to the Maurer's clefts because none of the vesicles observed could be labeled with antibodies against any Maurer's clefts protein (21,36). Whether these proteins travel via a nontypical vesicular transport or as soluble chaperoned protein complexes (76,81,114) remains to be shown, and recently described J-dots carrying parasitederived HSP40 and HSP70 proteins might play a role in this process (49,50).…”

“…Only a few proteins are known to be trafficked to structures in the host cell without passing through the Maurer's cleft hub. These proteins include MAHRP2 at tether-like structures (48), heat shock protein 40 (HSP40) and HSP70-x in or at J-dots (49,50), and some soluble proteins in the cytosol, such as ring exported protein 3 (REX3) (40). Although most resident proteins are encoded by single-copy genes, such as membrane associated histidine rich protein 1 (MAHRP1) (41) or knob associated histidine rich protein (KAHRP) (38, 51), Maurer's clefts gain their importance as sorting stations of a number of exported protein families.…”