Characterization of a Glutathione Metabolic Mutant of Mycobacterium tuberculosis and Its Resistance to Glutathione and Nitrosoglutathione

Abstract

ABSTRACT Glutathione is a tripeptide and antioxidant, synthesized at high levels by cells during the production of reactive oxygen and nitrogen intermediates. Glutathione also serves as a carrier molecule for nitric oxide in the form of S -nitrosoglutathione. Previous studies from this laboratory have shown that glutathione and S -nitrosoglutathione are directly toxic to mycobacteria. Glutathione is not transported into the cells as a tripeptide. Extracellular glutathione is converted to a dipeptide due to the action of transpeptidase, and the dipeptide is then transported into the bacterial cells. The processing of glutathione and S -nitrosoglutathione is brought about by the action of the enzyme γ-glutamyl transpeptidase. The function of γ-glutamyl transpeptidase is to cleave glutathione and S -nitrosoglutathione to the dipeptide (Cys-Gly), which is then transported into the bacterium by the multicomponent ABC transporter dipeptide permease. We have created a mutant strain of Mycobacterium tuberculosis lacking this metabolic enzyme. We investigated the sensitivity of this strain to glutathione and S -nitrosoglutathione compared to that of the wild-type bacteria. In addition, we examined the role of glutathione and/or S -nitrosoglutathione in controlling the growth of intracellular M. tuberculosis inside mouse macrophages.