The upstream sequence segment of the C-terminal cysteine-rich domain is required for microneme trafficking of Plasmodium falciparum erythrocyte binding antigen 175

Abstract

Erythrocyte invasion is a critical step for survival of Plasmodium parasites, the causative agents of malaria, in their host and recognition of the host cell receptors by Plasmodium erythrocyte-binding-like (EBL) proteins plays an important role. Although EBL subcellular localization was shown to be closely linked to parasite virulence in the rodent model of malaria, the trafficking of EBL to micronemes, the secretory organelle in the invasive parasite is not fully understood. In this study, we assessed the impact of the deletion and amino acid replacement of Plasmodium falciparum EBL (EBA-175) using transgenic P. falciparum lines expressing modified EBA-175. We found that, in addition to a signal peptide and a cysteine rich region (region 6) to the cytoplasmic tail, a previously unrecognized sequence segment in region 5 was required for correct microneme trafficking of EBA-175. Replacement of Arg or Phe residues in this segment altered microneme trafficking, suggesting that the sequence itself contained critical information. Based on these findings, we propose that the sequence segment in region 5 is also required for the recognition of EBA-175 by the trafficking machinery to direct this protein to the microneme. Our results provide key information to clarify an as yet unidentified EBA-175 trafficking mechanism.