Research Groups

Host generated anti-mycobacterial redox stress

Mammalian Biology: Immunology

Research Interests and Description

Research Scientist: Amit Singh, PhD

Research Interests

Molecular mechanisms underlying Mycobacterium tuberculosis dormancy and reactivation.

Description of Research

Mycobacterium tuberculosis (Mtb) is an extremely successful pathogen due to its ability to persist, and to latently infect more than one third of the world’s population. The increasing emergence of MDR-TB and XDR-TB is particularly disturbing and poses significant problems in the treatment and control of TB. How Mtb can persist in human tissues for decades without replicating and then abruptly resume growth and cause disease is a fundamental question in the TB field. Understanding the molecular mechanism(s) of Mtb dormancy and reactivation has become the focus of increased attention chiefly because Mtb persists in a state of “drug unresponsiveness”.
The role of oxygen tension in Mtb persistence has received wide attention because Mtb persists for decades under low oxygen (O2) tension in caseous granulomas and reactivates in the oxygen rich upper lobe of the lung. Studies have revealed that a rapid shift from aerobic to an O2-deficient environment results in bacterial death. However, the bacilli survive upon gradual depletion of O2, indicating that an ordered metabolic shutdown is necessary for adaptation to anoxia. Of particular interest, a significant degree of overlap exists between Mtb gene expression patterns seen in response to hypoxia and those observed after exposure to NO. These studies have revealed intriguing insights into the respiratory networks of Mtb that presumably lead to decreased energy production during in vivo adaptation.
Our long term goal is to understand the molecular mechanism of the way in which NO and hypoxia is sensed by Mtb to induce metabolic adaptation for long term persistence. The focus of the lab is to identify one or more sophisticated “sensor systems” required by Mtb to precisely monitor and respond to environmental signals such as O2 and NO, to promote persistence or reactivation. Our work suggests that the Mtb WhiB family functions as a Fe-S based “sensor system” to precisely monitor O2, NO and cellular redox stress to promote bacterial persistence. Recently, we have fully characterized WhiB3 (homologue of a Streptomyces protein required for sporulation) as the first intracellular redox sensor from Mtb. Mtb WhiB3 contains a redox-responsive [4Fe-4S]2+ cluster that senses and integrates the environmental signals O2 and NO by a novel redox switching mechanism with the production of complex virulence lipids essential for modulating host innate immunity. We plan to further investigate the function of the WhiB proteins in controlling dormancy and reactivation of Mtb. We will exploit EDFS-EPR to analyze the Fe-S clusters of WhiB proteins and utilize a novel protein interaction technology, Mycobacterial-Protein Fragment Complementation (M-PFC), to generate an extensive network of proteins which communicate with the WhiB proteins. We will analyze the regulatory role of WhiB proteins in response to oxido-reductive stress. Lastly, our plan is to investigate the in vivo role of the WhiB family using various animal models.
HIV infection and oxidative stress
Our lab is focused on developing a series of non-invasive biosensors to measure redox changes associated with HIV infection in real-time. This study may lead to the development of more affordable anti-oxidant based strategies for the control of AIDS.

Recent Publications

Ahmad, F.K., Chandra, P., Chopra, A., Siddiqui, Z., Bhaskar, A., Singh, A., Kumar, D. 2011. Express path analysis identifies tyrosine kinase Src centric network regulating divergent host responses to mycobacterium tuberculosis infection. J Biol Chem In press PubMed link

Farhana, A., Guidry, L., Srivastava, A., Singh, A., Hondalus, M.K., Steyn, A.J. 2010. Reductive stress in microbes: implications for understanding Mycobacterium tuberculosis disease and persistence. Adv Microb Physiol 57, 43-117 PubMed link

Singh, A., Crossman, D.K., Mai, D., Guidry, L., Voskuil, M.V., Renfrow, M.B., Steyn, A.J.C. 2009. Mycobacterium tuberculosis WhiB3 maintains intrabacterial redox homeostasis by modulating virulence lipid anabolism to subvert innate immunity. PLoS Pathog 5, e1000545 PubMed link

Singh, A., Guidry, L., Narasimhulu, K.V., Mai, D., Trombley, J., Redding, K.E., Giles, G.I., Lancaster, J. Jr., Steyn, A.J.C. 2007. Mycobacterium tuberculosis WhiB3 responds to O2 and nitric oxide via its [4Fe-4S] cluster and is essential for nutrient starvation survival. Proc Natl Acad Sci USA 104, 11562-11567 PubMed link

Singh, A., Mai, D., Kumar, A., Steyn, A.J.C. 2006. Dissecting virulence pathways of Mycobacterium tuberculosis through protein-protein association. Proc Natl Acad Sci USA 103, 11346-11351 PubMed link

Singh, R., Singh, A., Tyagi, A.K. 2005. Deciphering the genes involved in pathogenesis of Mycobacterium tuberculosis. Tuberculosis 85, 325-335 PubMed link