2003 IRISH SCIENTIST YEAR BOOK

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University of Limerick
Jakki Cooney & Todd Kagawa
Structural dissection of bacterial virulence

A demonstration of the key stages of structure determination for the Streptococcal cysteine proteinase SpeB. From left to right: A. Crystals of the SpeB protein, B. X-ray diffraction data, C. density map, and D. built model of the protein
See below for C. and D.

The bacterium Streptococcus pyogenes , also known as Group A Streptococcus (GAS), is the bacterium that causes Strep sore-throat. This is a common infection which is not life threatening and which currently responds well to standard antibiotic therapy. However, GAS also causes less benign diseases such as Streptococcal toxic shock, and necrotizing fasciitis ('flesh-eating disease'). These invasive diseases are not very common; however, they have high mortality rates (approx 30%). They are difficult to diagnose and the progression of the disease is very rapid. Furthermore, these invasive diseases do not respond well to standard antibiotic therapies.

During infection, the bacterial cells produce a variety of agents that are detrimental to the human host. Some of these agents are proteins that aid the bacterial cell to adhere to and/or invade human tissue, or are involved in avoiding detection by the host immune system; others are involved in tissue destruction. The purpose of our studies is to design specific inhibitors targeting bacterial factors and develop novel approaches in combating disease. Using a combination of molecular biological, protein chemistry and structural biology, studies on proteins involved at various stages of the pathogenic process are being undertaken at the University of Limerick.

Solution of protein structure was achieved using X-ray crystallographic methods. The naturally occurring precursor form of the Streptococcal cysteine proteinase, SpeB, was solved at atomic level resolution, which provided a 3D image of the protein molecule. Information provided by analysis of the structure showed that the propeptide-protease interaction was different from those observed in related eukaryotic proteins. Furthermore, the fine detail architecture of the SpeB active site is different. These two findings have allowed development of specific inhibitors of the SpeB protease. It has also allowed structure/ function analysis of key residues involved in stability of the zymogen, a naturally inhibited precursor of an enzyme (e.g. protease), and those contributing to the active site cleft. These studies provide information which drive inhibitor design experiments.


Contact: Dr. Jakki Cooney; Dr. Todd Kagawa; Department of Chemical and Environmental Sciences, University of Limerick. E-mail: [email protected] ; [email protected]