The role of thioredoxin proteins in Mycobacterium tuberculosis probed by proteome-wide target profiling

Mycobacterium tuberculosis encounters diverse microenvironments as it attempts to establish itself within its human host. The bacterium survives oxidative assault (ROS and RNS) when it is inside the host macrophages. Redox sensory and regulation processes therefore assume significant importance, as these are essential processes for M. tuberculosis to survive under these hostile conditions. The thioredoxin system that maintains balance between the thiol/dithiol couple plays a key role in maintaining redox homeostasis in M. tuberculosis. The most explored function of the thioredoxin system is elimination of toxic molecules such as free radicals, while very little is known about its role in other metabolic processes. In the present study, we aimed to reduce the knowledge gap about the thioredoxin system in M. tuberculosis. We attempted to capture targets of all the thioredoxins (viz., TrxB and TrxC) and a thioredoxin-like protein, NrdH in M. tuberculosis under aerobic and hypoxic conditions by performing thioredoxin trapping chromatography followed by mass spectrometry. Targets were classified using the PANTHER classification system and most enriched processes were figured out using Gene Ontology analysis. We found that TrxC captured the maximum number of targets in both the physiological conditions. Also, we suggest that the thioredoxin system might play an important role in hypoxic conditions by targeting proteins responsible to sense and maintain hypoxic conditions. Furthermore, our studies establish a link between TrxB and iron-sulfur cluster biogenesis in M. tuberculosis. Ultimately, these findings open a novel avenue to target the thioredoxin system for screening new anti-mycobacterial drug targets. ImportanceTuberculosis (TB), an infectious disease caused by bacteria M. tuberculosis, is the leading cause of death in the list of infectious diseases. Worldwide 1.7 billion people are estimated to be infected with TB, containing active and latent cases. An alarming situation is that M. tuberculosis has developed resistance against one or many of the first line drugs leading to emergence of drug resistant or multidrug resistant TB. Novel drugs targeting the drug resistant bacteria is an urgent need to cure the disease. Our study provides the framework to identify new drug targets. The significance of our study is to understand the thioredoxin system in more details by identifying their target proteins, which might facilitate development of new anti-tubercular drugs.