The Maurer's cleft protein MAHRP1 is essential for trafficking of PfEMP1 to the surface of Plasmodium falciparum‐infected erythrocytes

Abstract

SummaryDuring the intra-erythrocytic development of Plasmodium falciparum, the parasite modifies the host cell surface by exporting proteins that interact with or insert into the erythrocyte membrane. These proteins include the principal mediator of cytoadherence, P. falciparum erythrocyte membrane protein 1 (PfEMP1). To implement these changes, the parasite establishes a protein-trafficking system beyond its confines. Membrane-bound structures called Maurer's clefts are intermediate trafficking compartments for proteins destined for the host cell membrane. We disrupted the gene for the membrane-associated histidine-rich protein 1 (MAHRP1). MAHRP1 is not essential for parasite viability or Maurer's cleft formation; however, in its absence, these organelles become disorganized in permeabilized cells. Maurer's cleft-resident proteins and transit cargo are exported normally in the absence of MAHRP1; however, the virulence determinant, PfEMP1, accumulates within the parasite, is depleted from the Maurer's clefts and is not presented at the red blood cell surface. Complementation of the mutant parasites with mahrp1 led to the reappearance of PfEMP1 on the infected red blood cell surface, and binding studies show that PfEMP1-mediated binding to CD36 is restored. These data suggest an important role of MAHRP1 in the translocation of PfEMP1 from the parasite to the host cell membrane.

A subset of group A-like var genes encodes the malaria parasite ligands for binding to human brain endothelial cells

“…Two of these genes, MAHRP-1 and PF14_0752 (PHISTa), also were modestly up-regulated in IT parasites selected for rosetting (25). An indirect role for MAHRP-1 in cytoadherence already had been demonstrated, because deletion of the gene leads to depletion of surface-exposed PfEMP1 (46). PF14_0752 is part of the PHISTa subfamily, whose members are specific to P. falciparum (37).…”

Export of PfSBP1 to the Plasmodium falciparum Maurer’s Clefts

“…Mutating residues 2-9, 10-14, 21-26, 27-31 and 32-35, respectively, did not affect trafficking of the chimeric protein to the Maurer's clefts ( Figure 5B). In comparison, introducing alanines at positions 16-20 (A [16][17][18][19][20] seemed to reduce the trafficking efficiency. Now, fluorescence was seen in a dotted pattern surrounding the parasite body and in the Maurer's clefts ( Figure 5B).…”

“…To test this hypothesis, we extended the alanine replacements creating A [10][11][12][13][14][15][16][17][18][19][20] and A [16][17][18][19][20][21][22][23][24][25][26] ( Figure 5A). A [10][11][12][13][14][15][16][17][18][19][20] exhibited the same partial phenotype as did A [16][17][18][19][20] ( Figure 5B). In comparison, substituting amino acids 16-26 by alanines ( Figure 5B) completely abrogated trafficking of the corresponding protein to the Maurer's clefts.…”

“…These proteins are all expressed early during intraerythrocytic development and seem to be accessory or structural components of the trafficking machinery. For example, knockout studies have shown that PfSBP1 and MAHRP-1 are necessary for the trafficking of the immunovariant adhesin PfEMP1 to the erythrocyte surface (18)(19)(20). PfREX-1 seems to play a role in Maurer's cleft morphology (21).…”

Maurer's clefts, the enigma of Plasmodium falciparum

“…This finding was the first proof that Maurer's clefts have a function as an intermediate compartment in transport or sorting of proteins, at least for those destined for the erythrocyte membrane. Erythrocytes infected with parasites lacking MAHRP1 showed widened and fragmented clefts by electron microscopy that indicated a stabilizing role for MAHRP1 (123). Deletions of REX1 and truncation mutants showed a stacked Maurer's clefts phenotype similar to parasites of the D10 strain, which has a naturally occurring deletion of parts of chromosome 9, including all of the REXencoding genes (44).…”