Kelli Hvorecny (University of Washington)| Joel Quispe (University of Washington)| William Hardin (University of Washington)| Germain Alas (University of Washington)| Alex Paredez (University of Washington)| Justin Kollman (University of Washington)
Current treatments for the unicellular parasite Giardia lamblia, which infects over 300 million people annually, target all anaerobic organisms in the gut, decimating the commensal flora of patients and leading to other pathologies, including irritable bowel syndrome. Further, 20% of infections are resistant to front-line treatment. Thus, there is a need for new targets in the development of anti-Giardia therapies. Actin from Giardia is one potential target. In canonical eukaryotic systems, the tight conservation of actin underscores the fundamental role that the protein plays in maintaining cell shape and forming cellular structures. While actin controls these processes in Giardia, the actin sequence from Giardia is the most divergent identified in eukaryotes to date, and small molecules that target canonical actin are ineffective in Giardia. Additionally, the parasite lacks all canonical actin-binding proteins, many of which are essential in other eukaryotes. This suggests that actin in Giardia avoided the evolutionary constraints faced by other eukaryotes. However, the divergence of actin in Giardia makes the protein and its regulatory network a potential therapeutic target. Using fluorescent microscopy, we visualize actin in the ventrolateral flange, a membrane protrusion resembling a lamellipodium involved in attachment by Giardia. Further, knockdown of actin decreases both the width of the flange and attachment by Giardia to a surface. We have begun biochemical and cryo-electron microscopy studies to explore how the large amount of variation in actin from Giardia affects actin filament structure, as well as electron cryotomography studies to examine the cytoskeletal architecture of the flange. Identifying functional properties that distinguish the actin cytoskeleton of Giardia from its vertebrate homolog will provide opportunities for new drugs that specifically target the parasite without harming the host all the while providing a natural experimental system to probe fundamental actin functions.
Support or Funding Information
NIH F32AI145111; NIH R01AI110708; University of Washington Office of Postdoctoral Affairs