Abstract: Autotransporters are a large superfamily of proteins produced by Gram-negative bacteria that consist of two domains. The N-terminal “passenger” domain is exposed on the cell surface and often mediates a virulence function. The C-terminal domain anchors the protein to the outer membrane and, like most bacterial outer membrane proteins, folds into a cylindrical structure known as a β barrel. It was proposed many years ago that the passenger domain is secreted through a channel formed by the covalently linked β barrel domain, but a variety of studies have challenged this hypothesis.

I will describe work from my laboratory that indicates that passenger domain secretion is promoted by the Bam complex, a hetero-oligomer that has been shown to catalyze the insertion of β barrel proteins into the outer membrane. This work suggests that the secretion of the passenger domain and the assembly of the β barrel domain are intimately linked. I will also describe recent evidence that autotransporter β barrel domains and other types of β barrel proteins that reside in the outer membrane are assembled by distinct pathways.

Suggested Readings:
1. Bernstein, H.D., 2015. Looks can be deceiving: recent insights into the mechanism of protein secretion by the autotransporter pathway. Mol. Microbiol. 97, 205–215.

2. Roman-Hernandez, G., Peterson, J.H., Bernstein, H.D., 2014. Reconstitution of bacterial autotransporter assembly using purified components. Elife 3, e04234.

3. Wilson, M.M., Anderson, D.E., Bernstein, H.D., 2015. Analysis of the outer membrane proteome and secretome of Bacteroides fragilis reveals a multiplicity of secretion mechanisms. PLoS One 10, e0117732.

4. Wilson, M.M., Bernstein, H.D., 2015. Surface-Exposed Lipoproteins: An Emerging Secretion Phenomenon in Gram-Negative Bacteria. Trends Microbiol.

Event Contact:
Dr. Daniel Slade