Biology subjects

Harrigan, O.

Publications and source records attributed to Harrigan, O..

3 recordsLinked to original sources

bioRxiv2025

In situ cryo-ET reveals restricted docking of intraflagellar transport at the base of the trypanosome flagellum

Cilia and flagella are conserved organelles essential for sensory and motility functions and are assembled and maintained by bidirectional intraflagellar transport (IFT) along the axoneme. In Trypanosoma brucei, IFT is concentrated at the flagellar base near the transition zone and is restricted to four microtubule doublets (MTDs) as it traverses from the transition zone to the axoneme before reaching the extra-axonemal structure, the paraflagellar rod (PFR), associated region. To gain an insight on its initial working model before IFT restriction occurs, we revealed the in situ architecture of the IFT complex during the initial and complete landing to the transition zone using cryo-focused ion beam (cryo-FIB) milling and cryo-electron tomography (cryo-ET). IFT proteins assemble into polymeric trains upon landing. However, in the proximal portion of the flagellum, subtomogram averaging revealed that each single train is associated with individual MTDs at variable A- or B-tubule positions. By using miniaturized and enucleated T. brucei zoids that preserve the full circular arrangement of MTDs without milling, we revealed an alternating but spatially restricted IFT train pattern during the landing process, resembling the anterograde train scaffold known in Chlamydomonas. Magnify expansion microscopy further confirmed this restricted distribution of IFT proteins at the basal pool. Depletion of the IFT component IFT46 protein reduced the number of simultaneously docked trains without altering the restricted landing spatial pattern. These findings reveal a previously unrecognized spatial regulation governing IFT train initiation at the flagellar base, which could operate independently of IFT-B structural integrity, bridging the gap between the IFT architecture and doublet-spatial docking prior to anterograde transport.

cell biology↗

bioRxiv2025

Cellular and molecular basis of PfCoronin function in artemisinin resistance in Plasmodium falciparum

Artemisinin-based therapies are central to malaria treatment, but their efficacy is threatened by the emergence of resistant Plasmodium falciparum strains. While the role of Pfkelch13 mutations in clinical resistance is well established, recent reports from Africa implicate Pfcoronin mutations in treatment failure, adding to the complexity of resistance mechanisms. Here, we show that PfCoronin, a non-essential actin regulator active during the ring-stage, facilitates efficient hemoglobin uptake. We demonstrate that resistance-associated Pfcoronin mutations disrupt PfCoronins interaction with PfActin and its ring-stage localization, leading to impaired endocytosis and reduced hemoglobin acquisition. PfCoronin and PfKelch13 function in distinct cellular regions; mutations in both converge to limit heme availability and artemisinin activation. Although PfCoronin is dispensable for parasite viability, our findings demonstrate that Pfcoronin mutations reduce endocytosis and modulate artemisinin susceptibility during the clinically relevant ring stage--highlighting how non-essential, temporally restricted proteins can shape antimalarial drug response and resistance.

cell biology↗

bioRxiv2025

An Essential Adaptor for Apicoplast Fission and Inheritance in Malaria Parasites

Blood-stage Plasmodium falciparum parasites rely on a non-photosynthetic plastid, the apicoplast, for survival, making it an attractive target for antimalarial intervention. Like the mitochondrion, the apicoplast cannot be generated de novo and must be inherited by daughter parasites during cell division. This inheritance relies on coordinated apicoplast positioning and fission, but the molecular mechanisms controlling these processes remain poorly understood. Here, we identify a previously uncharacterized P. falciparum protein (Pf3D7_0613600), which we name PfAnchor, as a key regulator of apicoplast fission. Using Ultrastructure Expansion Microscopy (U-ExM), we show that PfAnchor localizes to the apicoplast throughout the asexual blood-stage. Conditional depletion disrupts apicoplast fission, leading to incomplete cytokinesis and parasite death. Notably, loss of the apicoplasts elongated branched structure via azithromycin treatment rescues these defects, underscoring Anchors specific role in apicoplast fission. Immunoprecipitation identified an interaction with the dynamin-like GTPase PfDyn2, a key mediator of both apicoplast and mitochondrial fission, establishing PfAnchor as the first apicoplast-specific dynamin adaptor protein. Our findings define PfAnchor as an essential factor for apicoplast fission and inheritance in P. falciparum blood-stage parasites, highlighting parasite-specific organelle division as a potential vulnerability for therapeutic intervention.

cell biology↗