Lees, Rebecca Anne (2024) The role of merozoite surface protein 1 in Plasmodium falciparum egress from erythrocytes. PhD thesis, Birkbeck, University of London.
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Abstract
During the erythrocytic lifecycle of the malaria parasite P. falciparum, merozoites invade red blood cells (RBC) in which they replicate asexually. Daughter merozoites are eventually produced by a process called segmentation, then released in a lytic process known as egress to invade new RBCs. Merozoite Surface Protein 1 (MSP1) is an abundant GPI-anchored protein that decorates the merozoite surface membrane. Just before egress, MSP1 undergoes proteolytic maturation by a parasite serine protease called SUB1; the processing products remain associated at the merozoite surface where they form a complex with other partner proteins. Both MSP1 processing and complex formation are thought to be important for egress, and MSP1 has also been implicated in RBC invasion. However, the composition, structure and function of the MSP1 complex, and the precise role of SUB1 processing, are poorly understood. We report that conditional depletion of MSP1 results in defective egress but has no effect on rupture of the RBC and parasitophorous vacuole membrane or invasion of new RBCs by those merozoites that are released. Electron microscopic examination revealed that defective egress of the MSP1-null mutant could be due to a ‘bystander’ effect on parasite segmentation, perhaps due to loss of GPI from the outer leaflet of the parasite plasma membrane. To address MSP1 function in a more nuanced manner, we generated parasites conditionally expressing a mutant MSP1 refractory to SUB1 processing. These parasites also display abnormal egress, suggesting that SUB1-mediated cleavage is important for MSP1 function. To glean further insights into MSP1 function, we have purified the native protein complex in both SUB1 processed and unprocessed forms for analysis by single particle cryo-EM. Models of this structure in comparison to the published recombinant structure indicate the presence of partner proteins and the regions of MSP1 with which the partners interact. The N and C termini of SERA5 (p47p18), which remain associated after SUB1 processing, appear to bind cleaved MSP1 in proximity of the 38/42 cleavage site. Localisation of SERA5 p47p18 to the merozoite surface appears to aid merozoite dispersal at egress.
Metadata
| Item Type: | Thesis |
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| Copyright Holders: | The copyright of this thesis rests with the author, who asserts his/her right to be known as such according to the Copyright Designs and Patents Act 1988. No dealing with the thesis contrary to the copyright or moral rights of the author is permitted. |
| Depositing User: | Acquisitions And Metadata |
| Date Deposited: | 21 Jun 2024 14:24 |
| Last Modified: | 22 Jun 2024 13:13 |
| URI: | https://eprints.bbk.ac.uk/id/eprint/53747 |
| DOI: | https://doi.org/10.18743/PUB.00053747 |
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