Host Chaperones Are Recruited in Membrane-bound Complexes byPlasmodium falciparum

Abstract

The ability of malarial parasite to deploy proteins at the surface of infected erythrocytes is well known. After their synthesis within the parasite, the cargo proteins are exported from the parasite and carried across the erythrocyte cytoplasm to be delivered at the erythrocyte surface. Our knowledge about the mechanisms involved in this complex trafficking path is limited. We have addressed the involvement of chaperones in traffic across erythrocyte cytoplasm. Our analyses of the chaperones available to the parasite indicated that none of the reported chaperones of the parasite origin are present in the erythrocyte cytoplasm. The chaperones of the host (Hsp70, Hsp90, Hop60), on the other hand, were readily detected in the erythrocyte cytosol. Hypotonic lysis and detergent solubilization experiments indicated that unlike their soluble nature in normal erythrocytes, host chaperones are recruited in membrane-bound, detergent-resistant complexes in infected cells. The association of host-Hsp70 with detergent-resistant complexes was ATP-dependent. Importantly, host chaperones could be detected in knob-enriched fractions and could be cross-linked to the knob subunit, PfHRP1, in a large complex at the surface of the infected erythrocytes. Our results implicate host chaperones in the assembly of parasite proteins such as knob subunits at the erythrocyte surface.The cytoadherence property of Plasmodium falciparum-infected erythrocytes is central to the pathogenesis of malaria. The remodeled plasma membrane of the infected erythrocyte is mainly responsible for its ability to adhere to the vascular endothelium (1, 2). As part of the remodeling process, the parasite synthesizes and traffics several proteins to the erythrocyte membrane. Among these, proteins such as erythrocyte membrane proteins 1 and 3 (PfEMP1 and PfEMP3) 1 and histidine-rich protein (PfHRP1) are assembled in complexes identified as knobs, which form the sites of attachment to the endothelium (3). Understanding the trafficking and assembly steps of protein complexes at the surface of infected erythrocytes is an important priority in efforts to counter malaria.Very little is known about the mechanisms and components involved in trafficking parasite-encoded proteins to the erythrocyte membrane. Both, BFA-sensitive as well as BFA-insensitive routes of transport have been described for the delivery of parasite proteins (4-7). Atypical membrane elements like tubovesicular membranes (TVM), Maurer's clefts, and intraerythrocytic inclusions in the erythrocyte cytoplasm have been implicated in trafficking between the parasite and the erythrocyte surface (8, 9). The involvement of molecular chaperones in the erythrocyte cytoplasm is often suggested in facilitating the transport and assembly of proteins destined for the plasma membranes (10 -12). Several candidate chaperones belonging to the heat shock protein family have been identified in the parasite (13-19); however, only limited information is available about their localizations and possible functions. Most imp...

Heat Shock Protein 90 Function Is Essential for Plasmodium falciparum Growth in Human Erythrocytes

“…Reagents and Antibodies-Antisera to PfHsp70 and PfHsp90 were generated against the recombinant COOH-terminal fragments of proteins in rabbit (18). DSP was obtained from Pierce.…”

Functional Analysis of the Exported Type IV HSP40 Protein PfGECO in Plasmodium falciparum Gametocytes

“…As exported proteins need to cross several membranes to target to their final destinations, it is suggested that molecular chaperones, such as the heat shock protein 40-kDa (HSP40) family (also called DnaJ proteins), will be involved to help regulate protein transport (6,55,68). Traditionally, HSP40 proteins regulate the activity of HSP70 in a manner that facilitates the folding of proteins under both normal and stress response conditions (20,34,53,54,90).…”

The heat shock protein 40 family of the malaria parasite Plasmodium falciparum

“…In addition, Banumathy et al observed that KAHRP cofractionated with host chaperones in knob-enriched fractions, and human Hsp70 could be released from these complexes by addition of ATP (24). Taken together, this might indicate that Hsp40s are specifically recruited in membrane-bound and detergent-resistant complexes, and they may exert a function in the assembly of knobs in infected red blood cells.…”

“…We therefore have to assume that, if the exported plasmodial type II Hsp40s provide a similar function in the red blood cell cytoplasm, the interacting partner would have to be human Hsp70. Banumathy et al (24) reported human Hsp70 in the P. falciparum infected erythrocyte to be present in detergent-resistant membranes. However, direct proof of interaction between P. falciparum Hsp40s and human Hsp70 is currently missing.…”