Artemisinin-based combination therapies (ACTs) have saved millions of lives and remain the cornerstone of treatment for Plasmodium falciparum malaria. However, parasites in Africa and Asia are now showing reduced susceptibility, threatening recent gains in malaria control. A central challenge is to understand how a parasite can evade a drug that is activated by its own biology.

        Artemisinin and its derivatives are prodrugs. Their antimalarial activity depends on cleavage of an endoperoxide bridge, a reaction largely driven by heme and ferrous iron within the parasite. In blood-stage infections, the major heme source is hemoglobin digestion in an acidic organelle called the digestive vacuole. The parasite ingests red blood cell cytoplasm, including hemoglobin, and delivers it to the digestive vacuole, where hemoglobin is broken down and free heme is released. Heme then reacts with artemisinin to generate highly reactive intermediates that damage parasite proteins and membranes. Conceptually, this creates a simple relationship: endocytosis-driven hemoglobin uptake → heme production in the DV → artemisinin activation. Any reduction in this uptake pathway weakens drug activation and favors parasite survival during artemisinin exposure.

        Over the past decade, mutations in Pfkelch13 have emerged as the major molecular marker of delayed parasite clearance in patients and increased ring-stage survival in vitro. These mutations are associated with altered endocytosis and reduced uptake of host cytoplasm into the early ring-stage parasite. Our interest in another gene, PfCoronin, began with an unexpected, highly reproducible observation. While selecting P. falciparum lines of Senegalese origin in vitro under artemisinin pressure, we repeatedly recovered parasites carrying mutations in Pfcoronin. Strikingly, these lines did not acquire canonical Pfkelch13 resistance mutations. At the time, PfCoronin’s role in infected red blood cells was poorly understood, but the consistency of Pfcoronin mutations under drug pressure suggested a functional connection to hemoglobin uptake and, by extension, to artemisinin activation.

        PfCoronin belongs to the coronin family of actin-associated proteins, which regulate cytoskeletal organization and membrane trafficking across many organisms. Unlike most eukaryotes, which encode multiple coronins, P. falciparum appears to have only a single coronin ortholog, making PfCoronin non-redundant. Yet previous knockout studies suggested that PfCoronin is not strictly essential for asexual blood-stage growth under standard in vitro conditions. This unusual combination—a unique, actin-related protein that seems dispensable for basic growth yet repeatedly mutates under artemisinin selection—motivated us to probe its function more deeply in the context of hemoglobin endocytosis.

        We first asked where PfCoronin is located within the parasite and what it interacts with. Using tagged parasite lines and ultrastructure expansion microscopy in collaboration with Dr. Sabrina Absalon (Indiana University School of Medicine, USA), we found that in wild-type parasites, PfCoronin is enriched at the parasite periphery, in the digestive vacuole, and on vesicle-like structures that contain host-derived material. Biochemical analyses identified PfActin as a major interacting partner. These data pointed toward a role for PfCoronin in organizing actin‑dependent endocytic and trafficking processes, particularly in the very early ring stages that are most relevant for artemisinin susceptibility critical.

        Introducing artemisinin-associated PfCoronin mutations fundamentally altered this picture. In mutant parasites, PfCoronin’s characteristic peripheral and vesicular pattern was disrupted, and overall PfCoronin protein levels were significantly reduced. Its interaction with PfActin was impaired, and PfActin abundance was specifically decreased in early rings. Moreover, these mutants were hypersensitive to perturbations in actin dynamics. Together, these findings support a model in which PfCoronin coordinates actin-driven endocytosis and trafficking in young rings, and in which resistance-associated mutations compromise this role, reducing the upstream flow of hemoglobin to the digestive vacuole.

        We next examined how this altered actin organization impacts parasite physiology. By quantifying host-cell material uptake in very young rings, we found that PfCoronin mutant parasites internalized significantly less red blood cell cytoplasm than wild-type parasites. Notably, the magnitude of this defect was comparable to that observed in parasites carrying PfKelch13 mutations, which are known to impair the cytostome, the parasite’s primary structure for ingesting host cytoplasm. Thus, two distinct proteins—PfKelch13 and PfCoronin—appear to converge on a shared functional outcome: reduced hemoglobin uptake during the early ring stage, and therefore reduced delivery of the heme-generating substrate to the DV.

        This reduction in endocytosis has direct consequences for artemisinin action. If less hemoglobin is delivered to the digestive vacuole, less heme is generated, and artemisinin activation is reduced. Consistent with this mechanism, PfCoronin mutant parasites exhibited increased survival in the ring-stage artemisinin assay, but this effect was tightly restricted to the early ring window, when hemoglobin uptake is most critical. Later developmental stages remained largely unaffected, mirroring the well-known stage specificity that defines artemisinin resistance.

        Importantly, this adaptation carries a measurable cost. In the absence of drug pressure, PfCoronin mutant parasites were consistently outcompeted by wild-type parasites, even though their asexual life cycle timing remained broadly similar. This fitness trade-off—enhanced survival under artemisinin exposure but diminished competitiveness without it—likely reflects the central role of efficient hemoglobin uptake and trafficking in parasite biology: dialing down endocytosis protects against artemisinin activation but also limits access to this critical nutrient source.

        Our findings add a new layer to the understanding of artemisinin resistance. Rather than being driven solely by mutations in Pfkelch13, resistance can arise from a broader network of proteins that regulate hemoglobin uptake and its trafficking to the digestive vacuole, thereby controlling how much artemisinin is activated inside the parasite. PfCoronin, although not essential for basic in vitro growth, exerts strong control over early ring-stage endocytosis and thereby over the heme-dependent activation of artemisinin.

         More broadly, this work highlights endocytic and trafficking pathways as central, upstream determinants of artemisinin action. Proteins that a parasite can technically live without under ideal laboratory conditions may nonetheless have outsized influence on the efficiency with which hemoglobin is captured, transported to the DV, and converted into the heme that activates artemisinin. As ACTs continue to be deployed worldwide, understanding—and monitoring—this network of hemoglobin-uptake and trafficking factors will be critical for anticipating, tracking, and ultimately mitigating the spread of artemisinin resistance.  

        Read the full article: Ullah I et al. (2026) ‘Cellular and molecular basis of PfCoronin function in artemisinin resistance in Plasmodium falciparum’, Nature Communications. Available at: https://doi.org/10.1038/s41467-026-72834-6