Association of mycothiol with protection of Mycobacterium tuberculosis from toxic oxidants and antibiotics

Abstract

SummaryMycothiol, MSH or 1 D -myo -inosityl 2-( N -acetyl-Lcysteinyl)amido-2-deoxy-a -D -glucopyranoside, is an unusual conjugate of N -acetylcysteine (AcCys) with 1 D -myo -inosityl 2-acetamido-2-deoxy-a a a a -D -glucopyranoside (GlcN-Ins), and is the major low-molecularmass thiol in mycobacteria. Mycothiol has antioxidant activity as well as the ability to detoxify a variety of toxic compounds. Because of these activities, MSH is a candidate for protecting Mycobacterium tuberculosis from inactivation by the host during infections as well as for resisting antituberculosis drugs. In order to define the protective role of MSH for M. tuberculosis , we have constructed an M. tuberculosis mutant in Rv1170, one of the candidate MSH biosynthetic genes. During exponential growth, the Rv1170 mutant bacteria produced ª ª ª ª 20% of wild-type levels of MSH. Levels of the Rv1170 substrate, GlcNAc-Ins, were elevated, whereas those of the product, GlcN-Ins, were reduced. This establishes that the Rv1170 gene encodes for the major GlcNAc-Ins deacetylase activity (termed MshB) in the MSH biosynthetic pathway of M. tuberculosis. The Rv1170 mutant grew poorly on agar media lacking catalase and oleic acid, and had heightened sensitivities to the toxic oxidant cumene hydroperoxide and to the antibiotic rifampin. In addition, the mutant was more resistant to isoniazid, suggesting a role for MSH in activation of this prodrug. These data indicate that MSH contributes to the protection of M. tuberculosis from oxidants and influences resistance to two first-line antituberculosis drugs.

Monocyte Differentiation, Activation, and Mycobacterial Killing Are Linked to Transsulfuration-dependent Redox Metabolism

“…In fact, sulfur metabolism has been implicated in mycobacterial virulence, antioxidant defense, and antibiotic resistance (27,28). The high proportion of genes encoding lipid biosynthetic functions that generate the diverse set of lipids found in mycobacteria suggest that sulfur acquisition from the host is critically important for microbial growth in the infected host.…”

Differential Expression of Mycothiol Pathway Genes: Are they Affected by Antituberculosis Drugs?

“…Therefore, mycothiol action may influence INH (isoniazid) action in M. tuberculosis, as was recently shown (11,13,14). Since INH is used for treatment of active TB cases and in prophylaxis of so-called latent TB cases, it would be important to understand the interaction between INH and mycothiol and the genes encoding enzymes responsible for the synthesis of mycothiol, since lack of mycothiol can contribute towards INH resistance (14). INH resistance is relatively common (15) and is usually attribu- We therefore investigated the expression and structure of the genes implicated in the biosynthesis and detoxification pathway of mycothiol in mycobacteria.…”

“…These authors hypothesized that this enzyme may furthermore play a role in the adaptive response to and detoxification of antibiotics. Therefore, mycothiol action may influence INH (isoniazid) action in M. tuberculosis, as was recently shown (11,13,14). Since INH is used for treatment of active TB cases and in prophylaxis of so-called latent TB cases, it would be important to understand the interaction between INH and mycothiol and the genes encoding enzymes responsible for the synthesis of mycothiol, since lack of mycothiol can contribute towards INH resistance (14).…”

Crystal Structures and Site-directed Mutagenesis of a Mycothiol-dependent Enzyme Reveal a Novel Folding and Molecular Basis for Mycothiol-mediated Maleylpyruvate Isomerization

“…It is believed that MSH functions similarly to GSH in many microbial activities (6). However, the understanding of MSH physiological function was limited to detoxification of reactive oxygen/alkalating species and to protection of pathogens such as Mycobacterium tuberculosis from host cell defense systems (1,7,8). Very recently, a novel physiological role of MSH in assimilation of aromatic compounds was described and an MSH-dependent maleylpyruvate isomerase (MDMPI) was identified in Corynebacterium glutamicum (9).…”

“…Mycothiol, also known as MSH 4 and chemically 1D-myo-inosityl-2-(N-acetyl-L-cysteinyl)-amido-2-deoxy-␣-D-glucopyranoiside (1)(2)(3)(4), is the major low molecule mass thiol in many groups of Gram-positive bacteria such as coryneform bacteria, mycobacteria, and streptomycetes (5,6). These bacteria synthesize MSH but lack GSH molecule that plays important roles in many physiological processes.…”