Investigating ribosome hibernation and activation during the infectious cycle of microsporidia

Ribosomes are the cellular protein-producing factories in all known life forms. They are central metabolic hubs and tightly regulated in response to physiological or environmental conditions. Protein biosynthesis is energy-expensive, consuming up to 40% of a cell's adenosine triphosphate (ATP). To survive shortages of ATP (e.g. caused by environmental or nutrient stress) cells can enter an energy-saving mode called dormancy, where most ribosomes are shifted into a “hibernating” state. Dormancy is typical for plant seeds or fungal spores that must endure drought or winter and underlies various infectious diseases and cancer. Dormancy is integral to life cycles of parasites that alternate between metabolically active phases inside hosts and dormant phases in the environment. A striking example is found in microsporidia—eukaryotic parasites capable of infecting a broad range of animals, including humans. Microsporidia exist as dormant spores in the environment, such as in contaminated water, and infect new hosts upon ingestion. During infection, microsporidia deploy a specialised invasion organelle, the polar tube (PT), to enter host cells. Fuelled by the host cell’s resources, the parasite then activates its metabolism, proliferates, and forms new dormant spores that ultimately kill the host cell and propagate the infection (Fig.1). Dormancy enables microsporidia to remain viable in the environment for weeks, poised to infect their next host. In humans, microsporidia are a health threat to immunocompromised individuals—including those with AIDS, transplant recipients, and malnourished children—causing chronic diarrhoea, wasting, and in severe cases, organ failure or brain infections leading to seizures. In agriculture, microsporidia devastate farmed animals such as fish and honeybees, endangering food security and agricultural economies. Despite their clinical and ecological importance, fundamental molecular questions about the microsporidian life cycle are poorly understood. For instance, how do microsporidia suppress most ribosomes to conserve energy during dormancy while keeping a subset active for survival? Equally mysterious is how ribosomes reactivate to power the parasite's protein metabolism during host invasion. This frontier biosciences proposal will quantify ribosomal activity and deconstruct the structural and mechanistic principles of ribosomal regulation across the microsporidian life cycle by harnessing the power of cutting-edge bioimaging and omics approaches. Our Objectives are to: O1: Study the structural basis of ribosome hibernation within dormant spores to determine the key factors that suppress most ribosomes O2: Map the dormant spore’s baseline ribosomal activity to decipher the minimum protein biosynthesis regime that keeps the spores alive O3: Investigate ribosome activation during host cell invasion to shed light on its triggers O4: Image the intracellular life cycle of microsporidia across scales to determine when protein biosynthesis is at its maximum and how ribosomes are switched off again when new spores are formed. To achieve these objectives, we will leverage an interdisciplinary and cutting-edge bioimaging and omics approach to advance knowledge of ribosome biology, cellular dormancy, and parasitic infection. This proposal unites a unique team of experts in microsporidian biology (Daum & Williams), structural biology (Daum & Isupov), omics (Williams), and bioimaging (Hacker & McLaren). The project will establish cutting-edge, multimodal pipelines, foster new skills, and train the next generation of researchers. Our proposal is poised to generate world-leading research that will contribute textbook-defining knowledge to the fields of microbiology, cell biology, and ribosome biology. Finally, our work will inspire innovations to combat parasitic infections, benefiting health care and food security.