Genesis of and Trafficking to the Maurer's Clefts of Plasmodium falciparum-Infected Erythrocytes

Abstract

Malaria parasites export proteins beyond their own plasma membrane to locations in the red blood cells in which they reside. Maurer's clefts are parasite-derived structures within the host cell cytoplasm that are thought to function as a sorting compartment between the parasite and the erythrocyte membrane. However, the genesis of this compartment and the signals directing proteins to the Maurer's clefts are not known. We have generated Plasmodium falciparum-infected erythrocytes expressing green fluorescent protein (GFP) chimeras of a Maurer's cleft resident protein, the membrane-associated histidine-rich protein 1 (MAHRP1). Chimeras of full-length MAHRP1 or fragments containing part of the N-terminal domain and the transmembrane domain are successfully delivered to Maurer's clefts. Other fragments remain trapped within the parasite. Fluorescence photobleaching and time-lapse imaging techniques indicate that MAHRP1-GFP is initially trafficked to isolated subdomains in the parasitophorous vacuole membrane that appear to represent nascent Maurer's clefts. The data suggest that the Maurer's clefts bud from the parasitophorous vacuole membrane and diffuse within the erythrocyte cytoplasm before taking up residence at the cell periphery.Plasmodium falciparum causes one of the most life-threatening infectious diseases of humans. Malaria is estimated to be responsible for up to 2 million deaths per year (34). The pathogenesis of the disease is associated with the intraerythrocytic cycle of the parasite, involving repeated rounds of invasion, growth, and schizogony. The erythrocyte provides a ready source of protein building blocks, but this quiescent cell provides little in the way of cellular architecture, as it possesses no internal organelles and no protein synthesis or trafficking machinery. As the parasite develops, it effectively remodels its adopted home by generating membranous structures outside its own cell and by implementing a complex and unusual system for transporting proteins across the host cell compartment and to its surface. This has led to particular interest in the membrane-bound compartments that appear in the red blood cell (RBC) cytoplasm as the parasite matures.Once the parasite has invaded a new host cell, it resides within a parasitophorous vacuole (PV). In the ring stage of intraerythrocytic growth, electron microscopy studies have revealed finger-like extensions of the PV membrane (5,11,43). These extensions are thought to remain connected to the PV and to develop to form a tubulovesicular network (TVN). As the parasite matures, disk-like structures appear at the RBC periphery, characterized by a translucent lumen and an electron-dense coat of variable thickness (4,11,22). These structures are referred to as Maurer's clefts, which is something of a misnomer, as they do not appear to be formed by invagina-

A Cluster of Ring Stage–specific Genes Linked to a Locus Implicated in Cytoadherence inPlasmodium falciparumCodes for PEXEL-negative and PEXEL-positive Proteins Exported into the Host Cell

“…Our data suggest, however, that the properties of the membranes of these two compartments are not identical and thus may not be continuous. Our FRAP analysis using REX2-GFP support previous FRAP studies using proteins transiently associating with Maurer's clefts (Knuepfer et al, 2005b) or the resident integral cleft protein MAHRP1 (Spycher et al, 2006). In each case, the data indicate that Maurer's clefts are separate entities.…”

“…Molecular Biology of the Cell 3620 tion and budding of nascent Maurer's clefts (Spycher et al, 2006), although other explanations for this phenomena are possible. These data show that a full-length PEXEL-negative protein fused to GFP can be exported into the host cell and correctly trafficked to the Maurer's clefts.…”

Development and host cell modifications of Plasmodium falciparum blood stages in four dimensions

“…The lack of detectable cleft formation from the early trophozoite onwards has important implications for protein export. It suggests that, at least after this stage, exported membrane proteins reach the clefts in other ways than through the formation of new clefts 2,17,18,22 . To confirm this, we used parasites expressing REX2 fused to the irre versibly photoconvertible protein Dendra2 (refs 46, 47).…”

“…Parasite induced vesicu lar structures in the host cell termed 'Maurer's clefts' are believed to serve as platforms for the trafficking of P. falciparum proteins to the host cell surface 14 . Maurer's clefts can be detected from the late ring stage onwards 5,15 and are thought to originate through budding from the PVM or from extensions of the PVM termed the tubove sicular network, their number increasing as the parasite progresses through the cycle 2,[16][17][18][19][20] . This forms the basis for one model that could solve a mechanistic problem in protein export in malaria parasites: although soluble proteins can pass through the recently described translocon at the PVM 21 , it was proposed that transmembrane pro teins are loaded into nascent Maurer's clefts forming at the PVM and are thereby exported with the new cleft 2,17,18,22,23 .…”

Protein trafficking in Plasmodium falciparum-infected red cells and impact of the expansion of exported protein families

“…MCs are parasite-induced, flattened membranous structures scattered throughout the cytoplasm of infected erythrocytes (Spycher et al 2006). However, it remains to be elucidated how the sorting of proteins to the RBC membrane and the surface of the iRBC occurs following protein traversal of the PVM.…”