Molecular Playground/ClyA

From Proteopedia

Introduction

Pore-forming toxins (PFTs) are virulence factors secreted by pathogenic organisms. These are proteins that form transmembrane channels on target cell membranes. They cause cell death by making the cell membrane permeable, leading to osmotic imbalance and lysis. There are two classes of PFTs based on their secondary structure, alpha-PFTs and beta-PFTs. Cytolysin A (ClyA) is an alpha-PFT and is secreted by Salmonella, Shigella and E. coli strains.

About Cytolysin A

1qoy is a 34 kDa monomer from Escherichia coli (E. coli). It is an alpha-PFT comprised of four alpha helicies, a smaller fifth alpha helix, and a beta tongue. The N-terminus and the C-terminus are highlighted. ClyA has been shown to form pores through a non-classical assembly pathway, excreted in oligomeric form in outer-membrane vesicles (OMV) as pre-pores. Only until ClyA reaches the target host membrane does it form the dodecameric PFT with hemolytic activity, possessing the ability to lyse the host cell.

The protomer of ClyA reveals slight differences between the monomer and protomer (from the dodecameric oligomer). The major conformational changes between the monomer and the protomer are the positions of the N-terminal helix and the beta-tongue. As ClyA oligomerizes and forms a pore, the N-terminal helix swings to the opposite side of the molecule while the beta-tongue changes its conformation and turns into an alpha-helix that interacts with the lipid bilayer.

Its crystal structure, 2WCD, reveals a dodecamer. Larger pores have been isolated, as well. A few research endeavors involving ClyA include using ClyA as part of cancer therapy, as well as a DNA delivery vehicle.

Research on ClyA at UMass Amherst

The Chen Lab recently published a paper on ClyA non-classical assembly. We use a technique commonly used for nanopore sensing called electrophysiology, which allows us to measure the ionic current through the ClyA nanopore.

Current ClyA projects focus on 3 main areas:

ClyA non-classical assembly and attack

ClyA engineered for cancer therapy

Studies of electro-osmosis using ClyA nanopore

References

1. Wallace, a J. et al. E. coli hemolysin E (HlyE, ClyA, SheA): X-ray crystal structure of the toxin and observation of membrane pores by electron microscopy. Cell 100, 265–76 (2000).

2. Atkins, a et al. Structure-function relationships of a novel bacterial toxin, hemolysin E. The role of alpha G. J. Biol. Chem. 275, 41150–5 (2000).

3. Mueller, M., Grauschopf, U., Maier, T., Glockshuber, R. & Ban, N. The structure of a cytolytic alpha-helical toxin pore reveals its assembly mechanism. Nature 459, 726–30 (2009).

4. Fahie, M. et al. A non-classical assembly pathway of Escherichia coli pore-forming toxin cytolysin A. J. Biol. Chem. 288, 31042–51 (2013).