Date of Award

1-11-2022

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Molecular Microbiology & Microbial Pathogenesis)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

Following invasion of a host red blood cell (RBC), the malaria parasite Plasmodium falciparum undertakes a program of dramatic host cell renovation. The parasite exports hundreds of effectors into the RBC, altering its shape and rigidity, increasing its permeability to nutrients, and constituting an intracellular transport network that traffics adhesins to the RBC surface. These adhesins mediate binding of the parasitized RBC to the host vascular endothelium, allowing the parasite to avoid destruction in the spleen, but contributing to the pathogenesis of cerebral malaria. Most of these exported effectors bear a pentameric amino acid sequence that marks them for protein export, called the Plasmodium export element (PEXEL), with consensus sequence RxLxE/Q/D. PEXEL is cleaved in the parasite endoplasmic reticulum (ER) by the aspartic protease plasmepsin V (PM V), a step necessary for export. Following cleavage, the new N-terminus is acetylated by some unknown N-acetyltransferase (NAT), the role of which remains unclear. For my Ph. D. thesis work, I used parasite genetics to interrogate the roles of these early players in the protein export pathway. First, I used a recently described post-transcriptional depletion method to lethally deplete PM V, finding this enzyme to be maintained by the parasite in substantial excess, and involved in an export-independent process that remains to be elucidated. Second, I used this depletion line to dissect PM V’s structure, finding that the enzyme requires an unusual nepenthesin insert to carry out its function. Finally, I searched for the PEXEL NAT, lethally depleting the likeliest candidate, and finding that it is required for parasite growth, but uninvolved in protein export. Taken together, this data provides further insight into how the parasite uses these ER-resident enzymes to enable its complex growth and protein sorting needs. Further, this serves as a foundation for future research, opening questions about the role of PM V, the nepenthesin insert’s contribution to PM V function (and protease function more generally), and the contribution of N-terminal acetylation to PEXEL function.

Language

English (en)

Chair and Committee

Daniel Goldberg

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Microbiology Commons

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