Uncovering the Roles ofMycobacterium tuberculosis melHin Redox and Bioenergetic Homeostasis: Implications for Antitubercular Therapy

Abstract

AbstractMycobacterium tuberculosis(Mtb), the pathogenic bacterium that causes tuberculosis, has evolved sophisticated defense mechanisms to counteract the cytotoxicity of reactive oxygen species (ROS) generated within host macrophages during infection. ThemelHgene inMtbandMycobacterium marinum(Mm) plays a crucial role in defense mechanisms against ROS generated during infection. We demonstrate thatmelHencodes an epoxide hydrolase and contributes to ROS detoxification. Deletion ofmelHinMmresulted in a mutant with increased sensitivity to oxidative stress, increased accumulation of aldehyde species, and decreased production of mycothiol and ergothioneine. This heightened vulnerability is attributed to the increased expression ofwhiB3, a universal stress sensor. The absence ofmelHalso resulted in reduced intracellular levels of NAD+, NADH, and ATP. Bacterial growth was impaired, even in the absence of external stressors, and the impairment was carbon-source-dependent. Initial MelH substrate specificity studies demonstrate a preference for epoxides with a single aromatic substituent. Taken together, these results highlight the role ofmelHin mycobacterial bioenergetic metabolism and provide new insights into the complex interplay between redox homeostasis and generation of reactive aldehyde species in mycobacteria.ImportanceThis study unveils the pivotal role played by themelHgene inMycobacterium tuberculosisandMycobacterium marinumin combatting the detrimental impact of oxidative conditions during infection. This investigation revealed notable alterations in the level of cytokinin-associated aldehyde,para-hydroxybenzaldehyde, as well as the redox buffer ergothioneine, upon deletion ofmelH. Moreover, changes in crucial cofactors responsible for electron transfer highlightedmelH’s crucial function in maintaining a delicate equilibrium of redox and bioenergetic processes. MelH prefers epoxide small substrates with a phenyl substituted substrate. These findings collectively emphasize the potential ofmelHas an attractive target for the development of novel antitubercular therapies that sensitize mycobacteria to host stress, offering new avenues for combating tuberculosis.