Bacteria use distinct mechanisms to inhibit SNARE-mediated membrane fusion
The intracellular transport of cargo and the subsequent fusion of cargo-loaded vesicles with their target compartments are essential for the function and survival of eukaryotic cells. The immune system in particular, is a complex network of secretory and endocytic events that orchestrate immune responses against invading pathogens as well as those against non-infectious particles like allergens. Pathogenic bacteria, such as Chlamydia trachomatis, inhibit membrane fusion events with the phagocytic pathway to circumvent the anti-bacterial immune response, thus impairing the ability of the immune system to clear the pathogen. Certain non-pathogenic bacteria also impair vesicular trafficking, yet this inhibition is beneficial to the host as it dampens inflammation and disease. Thus, interfering with membrane fusion has profound effects on the development of immune responses. The goal of this dissertation is three-fold. (i) Identify the SNARE proteins involved in phagocytosis and thus potential targets for intracellular bacteria. Using a mast cell-E. coli model of phagocytosis, we identify SNAP29 as a novel phagocytic SNARE. (ii) Elucidate the mechanism by which non-pathogenic bacteria inhibit mast cell secretion in the context of allergy. In this section, we show that the inhibition of mast cell secretion following Escherichia coli exposure is due to impaired exocytic SNARE complex formation. (iii) Determine how Chlamydia blocks membrane fusion events involved in phagosome maturation. Using biochemical and cellular approaches we demonstrate that the chlamydial protein IncA directly and specifically inhibits late endocytic SNARE-mediated membrane fusion. Furthermore, we identify a highly structured alpha-helical core that encodes the inhibitory and fusogenic functions of IncA. Ultimately, these results illustrate that both pathogenic and non-pathogenic bacteria regulate immune cell function through the manipulation membrane fusion events. These findings have potential implications for the development of novel anti-bacterial therapeutics and the management of hyperactive immune disorders.
Wesolowski, Jordan, "Bacteria use distinct mechanisms to inhibit SNARE-mediated membrane fusion" (2015). ETD Collection for Thomas Jefferson University. AAI3705122.