Exported proteins and their role in Plasmodium infection

• Main Author: Loh, Han Ping
• Other Authors: Peter Rainer Preiser
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: Science::Biological sciences::Molecular biology
• Online Access: https://hdl.handle.net/10356/100418; http://hdl.handle.net/10220/49978
• Institution: Nanyang Technological University

Malaria is caused by the protozoan genus Plasmodium and infects about 200 – 300 million people annually. Due to the rise in drug resistance in malaria parasites, it is of utmost importance to develop an effective vaccine that can confer sterile protection in humans. Although extensive efforts to develop vaccines are underway, current vaccine strategy based on malaria antigens failed to confer substantial protection in humans. The failure of current vaccine candidates to confer protection implies that the antigens associated with protection are still unknown. In order to try and address this problem, my project focuses on two approaches to study antigens and their impact on the immune system. The first is an untargeted approach method in which immune sera were screened to identify antigens which are highly associated with protection. The second method is a targeted approach focusing on the studying of the Plasmodium interspersed repeat (pir) multigene family using the rodent malaria parasite (RMP) Plasmodium yoelii as a model organism to understand the impact these proteins play in immunity. The pir multigene family was chosen for the targeted approach due to the variant nature of these protein which suggested that these proteins might be exposed to the immune system and therefore are under immune pressure. From the untargeted approach, we intend to elucidate the mechanism of protective immunity by using a malaria mouse model to identify potential parasite antigens that can confer sterile protection in mice. A prior study in our lab had generated a library of parasite antigens that are recognized by the sera from sterile protected mice. Based on this data, I have shortlisted three novel proteins which are highly associated with protection. I show that these three proteins are found within the parasite throughout the erythrocytic lifecycle and are present in the free merozoites as well. However, none of these three proteins could protect mice from the lethal P. yoelii YM infection. Interestingly many of the hits in the screen are parasite proteins found within the merozoites, suggesting that immunity against P. yoelii infection is directed towards the merozoite stages rather than the erythrocytic stage. For the second part of the project, I aimed to study the Plasmodium interspersed repeat (PIR) multigene family and its role in malaria infection. The pir multigene family is the largest multigene family in Plasmodium however research on these proteins is hampered by the inability to study these genes in isolation. Using the rodent malaria parasite P. yoelii orthologs known as yir, I aim to constitutively activate a single yir gene to study its functional role. In this study, I had successfully adopted a skip peptide approach to constitutively activate a single member of the yir gene within the parasite. RNAseq data showed that activation of a single yir caused a global silencing of the majority of yirs within the parasite population. I also observed that the activation of a single yir variant resulted in the upregulation of 4 additional yirs in the population. Analysis of the YIR protein sequence revealed that the YIRs which are co-regulated contain a PLASMED motif. The exact mechanism of how these PLASMED containing YIRs are co-regulation is currently unclear; however, my results suggest that there are subsets of yirs in the parasite which are regulated independently.