Grant: Discovery Grants Program - Individual

The primary goal of the proposed research is to characterize proteins that protect organisms against oxidative stress. For over 20 years, research in the Loewen laboratory has been focused on monofunctional catalases and bifunctional catalase-peroxidases which have as their main physiological role the degradation of potentially toxic hydrogen peroxide to harmless water and oxygen. Work has progressed from bacterial genetic analysis, through molecular genetic characterization to protein structure determination and has provided a greatly improved understanding of how the enzymes respond to physiological challenge in different organisms. The recent adoption of protein X-ray crystallography procedures in the laboratory has made it possible to address questions about the catalytic mechanisms operating in the enzymes; the proposed research will continue in this direction. The goal of the proposed research is to characterize factors that protect organisms against hydrogen peroxide and the specific objectives are to characterize and rationalize structural features that affect the catalytic mechanisms in catalase-peroxidases and monofunctional catalases. The bifunctional catalase-peroxidases have gained considerable notoriety from their role as the activator of the widely used anti-tubercular pro-drug isoniazid. In particular, strains of M. tuberculosis lacking the enzyme are resistant to the drug, giving rise to the most common cause of the spread of isoniazid-resistant tuberculosis and producing a serious health risk. One branch of the proposed research will focus on defining the catalytic mechanism involved in isoniazid activation. The research will enhance our knowledge of enzyme catalysis by providing a better understanding of the mechanisms of hydrogen peroxide degradation and of isoniazid activation as a drug against tuberculosis.