The major focus of this group's work currently is to solve the atomic resolution structure of alpha toxin. Alpha-toxin is implicated in diseases such as gas gangrene and cot death. It is one of the twelve toxins produced by the anaerobic bacterium C. perfringens to maintain its environment. Gas gangrene develops in anoxic environments, such as wounds, suitable for the bacteriums growth. The major tissue damage associated with the disease is probably caused by the actions of alpha-toxin, as described below.
Enzyme is kindly supplied by Julie Miller and Rick Titball from CBDE, Porton Down. Last year some of us presented the progress to date at the XVIIth congress of the International Union of Crystallography in Seattle, WA. Things have moved on since then and we now have a partially refined model of the 370 amino acid proten.
Alpha-toxin is actually a phospholipase C. It is dependent on two to three zinc atoms and possibly calcium. It is haemolytic, necrotic and lethal. Its main activity is believed to be cleavage of phospholipids in the cell membrane, and its toxic effects are thought to be primarily the result of its rapid action, which destroys the membrane more quickly than it is replaced by the cell's biosynthetic pathways. However, one of the products of the reaction, diacyl glycerol, also interacts with and disrupts the cell's second messenger systems.
Alpha-toxin has two domains. The n-terminal domain shares a 30% identity with another, non-toxic phospholipase C, from Bacillus cereus . The structure of this protein was solved by Hough et al , in 1989. It is an all helical protein, with three zinc ions at the active site, which are bound by a series of conserved histidines and aspergines. Additionally, the N-terminal tryptophan is involved in metal binding. The B. cereus structure is illustrated below.
The c-terminal domain of alpha-toxin shows homology to the n-terminal domain of human arachidonate 5-lipoxygenase, (HA5L) which is involved in the immune response. The structure of HA5L is not known, and we hope our structure of alpha-toxin will be able to shed light on the structure/function of this protein.
This toxin has been linked to lots of different diseases. It's particularly assosciated with gas gangrene, so here's list of gangreneous sites.
