The Cytoplasmic Region of <i>Plasmodium falciparum</i> SURFIN_4.2 Is Required for Transport from Maurer’s Clefts to the Red Blood Cell Surface

Abstract

Background: Plasmodium, the causative agent of malaria, exports many proteins to the surface of the infected red blood cell (iRBC) in order to modify it toward a structure more suitable for parasite development and survival. One such exported protein, SURFIN4.2, from the parasite of human malignant malaria, P. falciparum, was identified in the trypsin-cleaved protein fraction from the iRBC surface, and is thereby inferred to be exposed on the iRBC surface. SURFIN4.2 also localize to Maurer’s clefts—parasite-derived membranous structures established in the RBC cytoplasm and tethered to the RBC membrane—and their role in trafficking suggests that they are a pathway for SURFIN4.2 transport to the iRBC surface. It has not been determined the participation of protein domains and motifs within SURFIN4.2 in transport from Maurer’s clefts to the iRBC surface; and herein we examined if the SURFIN4.2 intracellular region containing tryptophan-rich (WR) domain is required for its exposure on the iRBC surface. Results: We generated two transgenic parasite lines which express modified SURFIN4.2, with or without a part of the intracellular region. Both recombinant SURFIN4.2 proteins were exported to Maurer’s clefts. However, only SURFIN4.2 possessing the intracellular region was efficiently cleaved by surface treatment of iRBC with proteinase K. Conclusions: These results indicate that SURFIN4.2 is exposed on the iRBC surface and that the intracellular region containing WR domain plays a role on the transport from Maurer’s clefts to the iRBC membrane.

Tryptophan-rich domains of Plasmodium falciparum SURFIN4.2 and Plasmodium vivax PvSTP2 interact with membrane skeleton of red blood cell

“…However, NTC-4.2WRD2-GFP produced signals beyond the PVM with a diffused localization pattern in the iRBCs, which only partially co-localized with the Maurer’s cleft marker SBP1 and with PfEMP1, suggesting that it was likely transported beyond Maurer’s clefts and to the RBC cytosol or membrane (Fig. 1 b), a result that is consistent with previous reports [ 6 , 19 ].

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“…For another member SURFIN 4.1 , the N-terminal 50 amino acids, transmembrane domain, and adjacent intracellular region contain sufficient information for recruiting a recombinant protein into the classical ER/Golgi secretory pathway, and for efficient translocation across the PVM to the Maurer’s clefts [ 18 ]. The mechanism by which SURFIN proteins are anchored into the iRBC membrane has yet to be elucidated, but recombinant SURFIN 4.2 possessing the intracellular WRD can be cleaved by surface treatment of iRBC with proteinase K, suggesting the WRD of SURFIN 4.2 may be responsible for transport of the protein from Maurer’s clefts to the iRBC membrane [ 19 ]. Interestingly, intracellular region of Pf332 that is homologous to the SURFIN WRD is found to associate with actin filaments of RBC membrane skeleton [ 12 ].…”

Multiple charged amino acids of Plasmodium falciparum SURFIN4.1 N-terminal region are important for efficient export to the red blood cell

“…Ala replacement of Glu residues regarding export of PfHsp70x (SNNAEES) was also found to be essential as it led to the accumulation of this protein in the parasitophorous vacuole (PV) [30]. In the case of SBP1, Ala replacement of the N-terminal DEPTQLQDAVP (amino acid positions [16][17][18][19][20][21][22][23][24][25][26], which contains three negatively charged residues, stopped export of this protein [17]. A net negative charge of the N-terminal region at a neutral pH was proposed to be important for SBP1 export to Maurer's clefts (pI of N-terminal 35 amino acid residues of SBP1 is 4.50) [17].…”

“…Herein we report the presence of five charged amino acid residues (3 glutamic acid and 2 lysine residues) in the Nterminal sequence of SURFIN 4.1 that independently contribute to efficient export of recombinant mini-SURFIN 4.1 to Maurer's clefts. We also show that elements required for export of SURFIN 4.1 are conserved in the paralog SURFIN 4.2 , for which infected RBC (iRBC) surface exposure has been shown [18,21]. We additionally determined that the N terminal sequences of SURFIN 4.1 and SURFIN 4.2 are not processed during export to Maurer's clefts.…”

Selections, frameshift mutations, and copy number variation detected on the surf 4.1 gene in the western Kenyan Plasmodium falciparum population

“…1 ). Since the intracellular region containing WR domain has an important role for the iRBC surface expression in the case of SURFIN 4.2 [ 5 ], SURFIN 4.1 would be expressed on the iRBC surface only by P. falciparum isolates possessing WR domain. SURFIN 4.1 variants without WR domain would be expressed only on the merozoite surface.…”