Biology subjects

Swift, R. P.

Publications and source records attributed to Swift, R. P..

4 recordsLinked to original sources

bioRxiv2026

Acyl Carrier Protein is Essential for Apicoplast Biogenesis in Malaria Parasites Independent of Fatty Acid Synthesis

Acyl carrier protein (ACP) and its 4-phosphopantetheine prosthetic group canonically function as the soluble scaffold for acyl chain assembly and elongation during type-II fatty acid synthesis (FASII). Plasmodium malaria parasites retain a FASII pathway in the apicoplast organelle that has been the subject of considerable scrutiny and confusion. Although apicoplast FASII is essential for P. falciparum growth within mosquitoes and the human liver, this pathway is dispensable and largely inactive in blood-stage parasites that can scavenge host fatty acids. In contrast to FASII enzymes that can be disrupted without fitness defect, we report that knockout or ligand-dependent knockdown of apicoplast ACP is lethal to blood-stage P. falciparum, indicating an essential FASII-independent function. Loss of ACP impairs the biosynthesis of essential isoprenoid precursors and blocks apicoplast biogenesis. Using proximity biotinylation and biochemical interaction studies, we identified a key role for ACP in binding and stabilizing apicoplast pyruvate kinase II (PKII). This critical enzyme is the only known source of nucleoside triphosphates (NTPs) in this organelle and is required for isoprenoid synthesis and apicoplast biogenesis. Our work reveals that ACP knockdown results in destabilization and loss of PKII, which is sufficient to explain ACP essentiality in this stage. This work unveils essential ACP function at a key biochemical hub controlling broad apicoplast metabolism in malaria parasites that is independent of the canonical ACP role in FASII.

biochemistry↗

bioRxiv2024

tRNA modifying enzymes MnmE and MnmG are essential for Plasmodium falciparum apicoplast maintenance

The circular genome of the Plasmodium falciparum apicoplast contains a complete minimal set of tRNAs, positioning the apicoplast as an ideal model for studying the fundamental factors required for protein translation. Modifications at tRNA wobble base positions, such as xm5s2U, are critical for accurate protein translation. These modifications are ubiquitously found in tRNAs decoding two-family box codons ending in A or G in prokaryotes and in eukaryotic organelles. Here, we investigated the xm5s2U biosynthetic pathway in the apicoplast organelle of P. falciparum. Through comparative genomics, we identified orthologs of enzymes involved in this process: SufS, MnmA, MnmE, and MnmG. While SufS and MnmA were previously shown to catalyze s2U modifications, we now show that MnmE and MnmG are apicoplast-localized and contain features required for xm5s2U biosynthetic activity. Notably, we found that P. falciparum lacks orthologs of MnmC, MnmL, and MnmM, suggesting that the parasites contain a minimal xm5s2U biosynthetic pathway similar to that found in bacteria with reduced genomes. Deletion of either MnmE or MnmG resulted in apicoplast disruption and parasite death, mimicking the phenotype observed in {Delta}mnmA and {Delta}sufS parasites. Our data strongly support the presence and essentiality of xm5s2U modifications in apicoplast tRNAs. This study advances our understanding of the minimal requirements for protein translation in the apicoplast organelle. ImportanceThe apicoplast of Plasmodium falciparum is an ideal model for studying minimal translation machinery since it contains the fewest number of tRNA isotypes required for protein translation. In such reduced systems, tRNA modifications, particularly at the wobble anticodon position, are critical for proper decoding of mRNA codons by tRNAs. In this study, we investigated the enzymes responsible for the wobble modification xm5s2U in the apicoplast. Our findings reveal that only four enzymes are required in the apicoplast to carry out this modification, similar to the situation found in bacteria with highly reduced genomes. Based on their phylogenetic conservation, these four enzymes have been included in all proposed minimal genome concepts to date and it appears that the apicoplast has retained the same core machinery. Our findings provide novel insight into apicoplast biology and into minimal requirements for protein translation.

microbiology↗

bioRxiv2022

The Plasmodium falciparum apicoplast cysteine desulfurase provides sulfur for both iron sulfur cluster assembly and tRNA modification

Iron sulfur clusters (FeS) are ancient and ubiquitous protein cofactors that play fundamental roles in many aspects of cell biology. These cofactors cannot be scavenged or trafficked within a cell and thus must be synthesized in any subcellular compartment where they are required. We examined the FeS synthesis proteins found in the relict plastid organelle, called the apicoplast, of the human malaria parasite Plasmodium falciparum. Using a chemical bypass method, we deleted four of the FeS pathway proteins involved in sulfur acquisition and cluster assembly and demonstrated that they are all essential for parasite survival. However, the effect that these deletions had on the apicoplast organelle differed. Deletion of the cysteine desulfurase SufS led to disruption of the apicoplast organelle and loss of the organellar genome, whereas the other deletions did not affect organelle maintenance. Ultimately, we discovered that the requirement of SufS for organelle maintenance is not driven by its role in FeS biosynthesis, but rather, by its function in generating sulfur for use by MnmA, a tRNA modifying enzyme that we localized to the apicoplast. By complementing the activity of the parasite MnmA and SufS with a bacterial MnmA and its cognate cysteine desulfurase, we showed that the parasite SufS provides sulfur for both FeS biosynthesis and tRNA modification in the apicoplast. The dual role of parasite SufS is likely to be found in other plastid-containing organisms and highlights the central role of this enzyme in plastid biology.

microbiology↗

bioRxiv2021

Critical Role for Isoprenoids in Apicoplast Biogenesis by Malaria Parasites

Isopentenyl pyrophosphate (IPP) is an essential metabolic output of the apicoplast organelle in Plasmodium falciparum malaria parasites and is required for prenylation-dependent vesicular trafficking and other cellular processes. We have elucidated a critical and previously uncharacterized role for IPP in apicoplast biogenesis. Inhibiting IPP synthesis blocks apicoplast elongation and inheritance by daughter merozoites, and apicoplast biogenesis is rescued by exogenous IPP and polyprenols. Knockout of the only known isoprenoid-dependent apicoplast pathway, tRNA prenylation by MiaA, has no effect on blood-stage parasites and thus cannot explain apicoplast reliance on IPP. However, we have localized an annotated polyprenyl synthase (PPS) to the apicoplast lumen. PPS knockdown is lethal to parasites, rescued by IPP, and blocks apicoplast biogenesis, thus explaining apicoplast dependence on isoprenoid synthesis. We hypothesize that PPS synthesizes long-chain polyprenols critical for apicoplast membrane fluidity and biogenesis. This work critically expands the paradigm for isoprenoid utilization in malaria parasites and identifies a novel essential branch of apicoplast metabolism suitable for therapeutic targeting.

microbiology↗