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

<b>Background</b>: <i>Plasmodium</i>, the causative agent of malaria, exports many proteinsto the surface of the infected red blood cell (iRBC) in order to modify ittoward a structure more suitable for parasite development and survival. Onesuch exported protein, SURFIN_4.2, from the parasite of humanmalignant malaria, <i>P. falciparum,</i> wasidentified in the trypsin-cleaved protein fraction from the iRBC surface, andis thereby inferred to be exposed on the iRBC surface. SURFIN_4.2 alsolocalize to Maurer’s clefts – parasite-derived membranous structures establishedin the RBC cytoplasm and tethered to the RBC membrane – and their role intrafficking suggests that they are a pathway for SURFIN_4.2 transportto the iRBC surface. It has not been determined the participation of proteindomains and motifs within SURFIN_4.2 in transport from Maurer’sclefts to the iRBC surface; and herein we examined if the SURFIN_4.2 intracellularregion containing tryptophan-rich (WR) domain is required for its exposure on theiRBC surface. <b>Results</b>: We generated two transgenic parasite lineswhich express modified SURFIN_4.2, with or without a part of the intracellularregion. Both recombinant SURFIN_4.2 proteins were exported to Maurer’sclefts. However, only SURFIN_4.2 possessing the intracellular region wasefficiently cleaved by surface treatment of iRBC with proteinase K. <b>Conclusions</b>: These results indicate that SURFIN_4.2is exposed on the iRBC surface and that the intracellular region containing WRdomain plays arole on the transport from Maurer’s clefts to the iRBC membrane.

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

Background: <i>Plasmodium</i>, 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, SURFIN_4.2, from the parasite of human malignant malaria, <i>P. falciparum</i>, was identified in the trypsin-cleaved protein fraction from the iRBC surface, and is thereby inferred to be exposed on the iRBC surface. SURFIN_4.2 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 SURFIN_4.2 transport to the iRBC surface. It has not been determined the participation of protein domains and motifs within SURFIN_4.2 in transport from Maurer’s clefts to the iRBC surface; and herein we examined if the SURFIN_4.2 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 SURFIN_4.2, with or without a part of the intracellular region. Both recombinant SURFIN_4.2 proteins were exported to Maurer’s clefts. However, only SURFIN_4.2 possessing the intracellular region was efficiently cleaved by surface treatment of iRBC with proteinase K. Conclusions: These results indicate that SURFIN_4.2 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.

Positive Diversifying Selection on the <i>Plasmodium falciparum</i> <i>surf_4.1</i> Gene in Thailand

<i>Plasmodium falciparum</i> SURFIN_4.1 is a type I transmembrane protein thought to locate on the merozoite surface and to be responsible for a reversible adherence to the erythrocyte before invasion. In this study, we evaluated <i>surf_4.1</i> gene segment encoding extracellular region for polymorphism, the signature of positive selection, the degree of linkage disequilibrium, and temporal change in allele frequency distribution in <i>P. falciparum</i> isolates from Thailand in 1988–89, 2003, and 2005. We found that SURFIN_4.1 is highly polymorphic, particularly at the C-terminal side of the variable region located just before a predicted transmembrane region. A signature of positive diversifying selection on the variable region was detected by multiple tests and, to a lesser extent, on conserved N-terminally located cysteine-rich domain by Tajima’s <i>D</i> test. Linkage disequilibrium between sites over a long distance (> 1.5 kb) was detected, and multiple SURFIN_4.1 haplotype sequences detected in 1988/89 still circulated in 2003. Few of the single amino acid polymorphism allele frequency distributions were significantly different between the 1988/89 and 2003 groups, suggesting that the frequency distribution of SURFIN_4.1 extracellular region remained stable over 14 years.<br>

Positive Diversifying Selection on the <i>Plasmodium falciparum</i> <i>surf_4.1</i> Gene in Thailand

<i>Plasmodium falciparum</i> SURFIN_4.1 is a type I transmembrane protein thought to locate on the merozoite surface and to be responsible for a reversible adherence to the erythrocyte before invasion. In this study, we evaluated <i>surf_4.1</i> gene segment encoding extracellular region for polymorphism, the signature of positive selection, the degree of linkage disequilibrium, and temporal change in allele frequency distribution in <i>P. falciparum</i> isolates from Thailand in 1988–89, 2003, and 2005. We found that SURFIN_4.1 is highly polymorphic, particularly at the C-terminal side of the variable region located just before a predicted transmembrane region. A signature of positive diversifying selection on the variable region was detected by multiple tests and, to a lesser extent, on conserved N-terminally located cysteine-rich domain by Tajima’s <i>D</i> test. Linkage disequilibrium between sites over a long distance (> 1.5 kb) was detected, and multiple SURFIN_4.1 haplotype sequences detected in 1988/89 still circulated in 2003. Few of the single amino acid polymorphism allele frequency distributions were significantly different between the 1988/89 and 2003 groups, suggesting that the frequency distribution of SURFIN_4.1 extracellular region remained stable over 14 years.