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Wednesday, September 19, 2018 at 4:00pm
Clark Hall, 700
Andreas Gahlmann, University of Virginia
Host: Peng Chen
Towards a molecular-level understanding of bacterial type 3 secretion:
Resolving cytosolic complex formation in living cells using 3D single-molecule tracking
About a third of bacterial proteins are either transported across or integrated into the cell membranes, so that they can perform functions that are vital for bacterial survival in specific environmental niches. Directional transport of selected proteins often relies on large membrane-embedded biomolecular assemblies. For example, the dual membrane-spanning Type 3 Secretion System (T3SS) enables Gram-negative bacterial pathogens to inject so-called effector proteins directly into the cytosol of eukaryotic host cells – a virulence mechanism that currently results in more than 1 million human deaths per year. While the cocktail of injected effector proteins differs for each pathogen, the structural proteins of T3SSs are highly conserved, making Type 3 secretion systems a key target for the development of anti-virulence drugs that would provide valuable alternatives to broad-spectrum antibiotics in use today. Our research focuses on providing a detailed understanding of how membrane-embedded biomolecular assemblies, like the T3SS, are functionally regulated at the molecular level and how these assemblies ultimately enable bacterial survival and virulence. To achieve this goal, we use super-resolution optical imaging technologies, primarily single-molecule localization microscopy and lattice-light sheet microscopy, to investigate molecular-level spatial and temporal phenomena inside living bacterial cells and cellular-level phenotypes within developing microbial communities.
In this talk, I will describe how shaping of light waves enables measurements of 3D motion trajectories of individual bacterial proteins in living cells at high spatial and temporal resolution. Analyzing the trajectories of thousands of intracellular proteins allows us to resolve their prevalent diffusion states and the relative abundances of these states. Our results indicate that structural T3SS proteins are capable of forming distinct oligomeric complexes in the bacterial cytosol. Some, but not all, of these complexes are dependent on the presence of other T3SS proteins and they change upon functional activation of type 3 secretion. Resolving the cytosolic diffusion states of T3SS proteins that are directly associated with T3SS function provides a path towards describing the molecular basis of type 3 secretion in bacterial pathogens.