MULTISCALE ANALYSIS OF MYOSINA-BASED MOTILITY IN TOXOPLASMA GONDII

Toxoplasmic encephalitis (TE) is a life-threatening infection of the brain in AIDS patients caused by theopportunistic pathogen, Toxoplasma gondii. Drugs are available to treat acute T. gondii infection in thesepatients, and to suppress its re-emergence in those who are chronically infected, but for many patients theadverse effects of the drugs are severe, resulting in their discontinuation. Thus, there is a need to develop new,better-tolerated drugs to treat AIDS-related TE. This, in turn, requires a better understanding of the biology of T.gondii and the mechanisms underlying its virulence, so that critical points of vulnerability in the parasite?s lifecycle can be identified and targeted. The life cycle stage of T. gondii responsible for disease pathogenesis, the tachyzoite, is highly motile.Tachyzoite motility is required for host cell invasion, migration across biological barriers, and disseminationthrough host tissues. T. gondii MyosinA (TgMyoA) is an unconventional myosin motor protein that plays a centralrole in parasite motility, and tachyzoites lacking TgMyoA are completely avirulent. The overarching goals of thisproject are to advance our mechanistic understanding of tachyzoite motility and to test whether small moleculestargeting the motility machinery can ameliorate disease in an animal model of infection. The Specific Aims areto: (1) Determine how altering specific aspects of TgMyoA motor function affects parasite motility, bycharacterizing how recently identified small-molecule inhibitors of the TgMyoA motor affect its biomechanicalactivity and connecting these changes in motor function to effects on parasite 3D motility; and (2) Determine howinhibiting TgMyoA impacts parasite dissemination and disease progression, in vivo, to better understand the roleof TgMyoA and parasite motility during infection and to provide the first direct evaluation of the TgMyoA motoras a drug target for preventing or treating toxoplasmosis. Recent technological advances have created an unprecedented opportunity to manipulate and study parasitemotility in a truly integrated way. This project will capitalize on that opportunity across the full range of scales ?from the biochemical and biophysical properties of the TgMyoA motor, to the characteristics of parasite motilitywithin a model 3D extracellular matrix, to the ability of parasites to disseminate and cause disease in infectedanimals. The results will therefore significantly enhance our mechanistic understanding of how T. gondii moveswithin its hosts to cause disease. Because TgMyoA is both essential for virulence and distinctly different fromhuman myosins it is also a potential target for drug development; by directly testing the druggability of TgMyoAin an animal model of infection, this work will contribute to ongoing efforts to develop new and improvedchemotherapeutics for managing T. gondii infections in AIDS patients.