Molecular mechanism of tetanus neurotoxin pathogenesis

Project Summary Tetanus has been a major deadly infectious disease throughout human history. It is caused by the spore-forming anaerobic bacterial pathogen Clostridium tetani, which can germinate within the deep wound and produce a potent bacterial toxin known as tetanus neurotoxin (TeNT), which is the sole cause of tetanus’s characteristic spastic paralysis symptoms. The mysterious connection between deep puncture wounds and tetanus disease was already recognized by ancient civilizations. Modern studies have now established the structure and function of TeNT: it acts by first targeting motor nerve terminals and then mysteriously undergoes retrograde transport into the spinal cord and then re-enters inhibitory neurons and blocks inhibitory neurons, leading to hyperactivity of motoneurons and muscle spasms. However, how the toxin traffics into the spinal cord has remained a major mystery for over a century. Here our preliminary studies have identified potential host factors that may mediate trafficking of TeNT into the spinal cord and our proposal seeks to carry out a comprehensive set of studies to examine TeNT binding to host factors at the biochemical level, resolve the toxin-host factor complex structure using an X-ray crystal structure approach, examine co-trafficking of TeNT and host factors within compartmentalized neuronal cultures, and evaluate the role of host factors for TeNT in vivo dynamics and pathogenesis using genetically modified mouse models. Our proposed studies will establish the long-sought-after host factor that mediates trafficking and pathogenesis of TeNT in animal models, thus solving a century-old major puzzle in our understanding of tetanus etiology. Our studies may also reveal retrograde trafficking pathways important for neuronal health and for delivery of therapeutics into the central nervous system.