Perfringolysin O Recognition of Cholesterol in the Target Membrane

Some bacterial protein toxins function by binding to the surface of mammalian cells, inserting into the bilayer, and creating holes in the membrane that lead to cell death. Perfringolysin O (PFO) is secreted by Clostridium perfringens, the pathogenic bacteria that cause gas gangrene. PFO binds to cholesterol-containing membranes and oligomerizes to form large pores with diameters of ~300 Å. The C-terminus of PFO (domain 4) mediates its initial binding to the membrane, and this binding triggers the structural rearrangements required to initiate the oligomerization of PFO monomers.
Using multiple independent fluorescence techniques we are investigating the role of cholesterol in pore formation and the nature of the PFO-cholesterol interaction. For example, does PFO bind to a single cholesterol molecule or to a surface feature of a cholesterol-rich domain in the membrane? Is cholesterol required only for membrane binding, or it also plays an additional role in toxin oligomerization and/or membrane insertion? Given its unique ability to only detect high cholesterol levels in membranes, PFO constitutes an attractive tool to study the role of cholesterol and its regulation in cardiovascular diseases and other cholesterol related health problems.

Injection of Virulence Factors Through the Cell Membrane

Several pathogenic bacteria including Yersina ssp., Salmonella ssp., enterophatogenic E. coli, Pseudomonas aeruginosa, Shigella flexneri, etc., inject proteins directly into the eukaryotic cell cytoplasm to interfere with and to alter host processes. These proteins are presumably injected through the eukaryotic cell membrane via a proteinaceous transmembrane channel known as translocon, which is of bacterial origin. The translocons are thought to be transmembrane protein complexes consisting of several components. Our goal is to understand, at a molecular level, how the translocon is assembled into the target membrane and functions to translocate virulence factors into the cell cytoplasm.

We employ a variety of biophysical, biochemical, and molecular biological approaches to study protein structure, protein-membrane and protein-protein interactions.