The functional interplay of low molecular weight thiols in Mycobacterium tuberculosis

Abstract

BackgroundThree low molecular weight thiols are synthesized by Mycobacterium tuberculosis (M.tb), namely ergothioneine (ERG), mycothiol (MSH) and gamma-glutamylcysteine (GGC). They are able to counteract reactive oxygen species (ROS) and/or reactive nitrogen species (RNS). In addition, the production of ERG is elevated in the MSH-deficient M.tb mutant, while the production of MSH is elevated in the ERG-deficient mutants. Furthermore, the production of GGC is elevated in the MSH-deficient mutant and the ERG-deficient mutants. The propensity of one thiol to be elevated in the absence of the other prompted further investigations into their interplay in M.tb.MethodsTo achieve that, we generated two M.tb mutants that are unable to produce ERG nor MSH but are able to produce a moderate (ΔegtD-mshA) or significantly high (ΔegtB-mshA) amount of GGC relative to the wild-type strain. In addition, we generated an M.tb mutant that is unable to produce GGC nor MSH but is able to produce a significantly low level of ERG (ΔegtA-mshA) relative to the wild-type strain. The susceptibilities of these mutants to various in vitro and ex vivo stress conditions were investigated and compared.ResultsThe ΔegtA-mshA mutant was the most susceptible to cellular stress relative to its parent single mutant strains (ΔegtA and ∆mshA) and the other double mutants. In addition, it displayed a growth-defect in vitro, in mouse and human macrophages suggesting; that the complete inhibition of ERG, MSH and GGC biosynthesis is deleterious for the growth of M.tb.ConclusionsThis study indicates that ERG, MSH and GGC are able to compensate for each other to maximize the protection and ensure the fitness of M.tb. This study therefore suggests that the most effective strategy to target thiol biosynthesis for anti-tuberculosis drug development would be the simultaneous inhibition of the biosynthesis of ERG, MSH and GGC.

New roles for glutathione: Modulators of bacterial virulence and pathogenesis

“…This includes the upregulation of polyketide biosynthesis genes and ESX-1 secretion, which restricts phagosomal acidification and induces phagosomal rupture respectively [ 72 ]. This could explain why the M. tuberculosis ΔmshA mutant defective in mycothiol synthesis has lower expression of ESX-1 secretion system genes [ 73 ], and significantly lower intracellular bacterial loads in murine macrophages at later timepoints of a low dose of infection [ 74 ]. This demonstrates that M. tuberculosis utilizes the MSH redox system to respond to the acidic pH of the phagosomal compartment for its virulence.…”

From infection niche to therapeutic target: the intracellular lifestyle of Mycobacterium tuberculosis

“…The only attenuated growth defect of the MSH-deficient mutants in animal models suggest compensation by other LMW thiols, supported by earlier studies showing elevated production of MSH in other thiol-deficient Mtb mutants [ 110, 111 ]. Further investigations demonstrated that Mtb mutants deficient in more than one LMW thiol had the most severe growth defect in both human and mouse macrophages [ 112 ]. These results confirm the interplay of LMW thiols to maximize the protection of Mtb and sustain its survival in macrophages, and highlight their potential as therapeutic targets.…”

Redox homeostasis as a target for new antimycobacterial agents

“…One susceptible pathway in the bacterial cell is the thiol-based redox metabolism, which plays a key role in many cellular processes, including protection of the bacterial cell against endogenous and exogenous reactive oxygen species, proper protein folding, and DNA synthesis [9]. While glutathione (GSH) is rarely detected in pathogenic prokaryotes, ergothioneine (ERG) and mycothiol (MSH) are the most important low molecular weight thiols in mycobacteria [9], [10]. They preserve cellular homeostasis by maintaining a reducing environment, and function as detoxification agents against antibiotics, alkylating agents, electrophiles, and other reactive intermediates [10].…”