Targeting of the Ring Exported Protein 1 to the Maurer’s Clefts is Mediated by a Two‐Phase Process

Abstract

Early development of Plasmodium falciparum within the erythrocyte is characterized by the large‐scale export of proteins to the host cell. In many cases, export is mediated by a short sequence called the Plasmodium export element (PEXEL) or vacuolar transport signal; however, a number of previously characterized exported proteins do not contain such an element. In this study, we investigated the mechanisms of export of the PEXEL‐negative ring exported protein 1 (REX1). This protein localizes to the Maurer’s clefts, parasite‐induced structures in the host‐cell cytosol. Transgenic parasites expressing green fluorescent protein–REX1 chimeras revealed that the single hydrophobic stretch plus an additional 10 amino acids mediate the export of REX1. Biochemical characterization of these chimeras indicated that REX1 was exported as a soluble protein. Inclusion of a sequence containing a predicted coiled‐coil motif led to the correct localization of REX1 at the Maurer’s clefts, suggesting that association with the clefts occurs at the final stage of protein export only. These results indicate that PEXEL‐negative exported proteins can be exported in a soluble state and that sequences without any apparent resemblance to a PEXEL motif can mediate export across the parasitophorous vacuole membrane.

Export of PfSBP1 to the Plasmodium falciparum Maurer’s Clefts

“…In comparison to SBP full and the endogenous PfSBP1, the chimeric proteins A [16][17][18][19][20][21][22][23][24][25][26] and SBP Tm behaved differently. A [16][17][18][19][20][21][22][23][24][25][26] was exclusively present in the SLO pellet fraction ( Figure 8C). Some protein could be released into the supernatant after SLO/SAP treatment of the infected erythrocytes, albeit the vast majority of the protein was found in the SLO/SAP pellet fraction ( Figure 8C).…”

“…Given that this is only a partial phenotype, we hypothesized that a broader region might be responsible for export of PfSBP1 to the Maurer's clefts. 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 the case of PfREX-1, a hydrophobic stretch plus an additional 10 amino acids seem to be important for export (22). Unlike PfMAHRP-1, PfREX-1 seems to traverse the secretory pathway in a soluble state and only after delivery into the erythrocyte cytosol does the protein associate with the Maurer's clefts through a predicted coiled-coil motif (22).…”

“…For PfMAHRP-1, it has been suggested that the transmembrane domain and the second half of the N-terminus contain the signals for directing the protein in a membraneassociated state to the Maurer's clefts (16). In the case of PfREX-1, a hydrophobic stretch plus an additional 10 amino acids seem to be important for export (22). Unlike PfMAHRP-1, PfREX-1 seems to traverse the secretory pathway in a soluble state and only after delivery into the erythrocyte cytosol does the protein associate with the Maurer's clefts through a predicted coiled-coil motif (22).…”

PEXEL-independent trafficking of Plasmodium falciparum SURFIN4.2 to the parasite-infected red blood cell and Maurer's clefts

“…SBP1, MAHRP1 and REX2 lack a signal peptide but contain a transmembrane (TM) region which, along with sequences at their N-terminal region, has been implicated in protein transport [22 -24]; however, the hydrophobic N-terminal region of the REX1 protein has been shown to be the only region required for transport of this particular protein. [25].…”