PolTube · A molecular model of the microsporidian infection apparatus

Microsporidia are opportunistic fungal pathogens that infect organisms as evolutionarily divergent as protists and mammals. Due to their growing impact on the global food supply chain, the environment, and human health, these unusual spore-forming organisms have been classified as emerging pathogens of high priority. Intriguing cell biological features that are central to microsporidian infectivity and pose challenges to drug development are poorly understood due to a lack of structural information and the absence of genetic tools. As energy parasites, microsporidia survive with the smallest eukaryotic genome and without classical mitochondria through an obligate intracellular lifestyle. A fascinating infection mechanism, which involves a long, hollow protein structure, is essential for efficient host invasion. The microsporidia-specific infection apparatus consists of several structural proteins that form the polar tube, which is used to inject the entire cytoplasm from the infectious spore into the host cell. Here, we will use an innovative approach to provide the structural and mechanistic basis of the microsporidian infection mechanism by using cutting-edge structural biology techniques and novel developed in-vivo tools. By studying the endogenous polar-tube, we will identify new elements and provide an architectural model of the invasion organelle. Reconstitution and biochemical characterization of the major components of the polar tube, followed by high-resolution cryo-EM studies, will unravel the polar tube protein interaction network and provide near-atomic information to complement the architectural model. Together with the development of genetic methods to tag, visualize and manipulate components in-vivo, we will provide a comprehensive model of the infection process, give insights into the specialization and evolution of a fascinating and understudied organism and deliver ground-breaking tools to open new frontiers in microsporidian research.