Mycothiol regulates and is regulated by a thiol‐specific antisigma factor RsrA and σ^R in Streptomyces coelicolor

Abstract

SummaryMycothiol (MSH) is a small thiol molecule with a cysteine-ligated disaccharide structure found in actinomycetes that include streptomycetes and mycobacteria. In Streptomyces coelicolor, a model organism for antibiotic production and differentiation, the amount of MSH is under the control of a sigma factor s R , which is regulated by an antisigma factor RsrA with a thiol-disulphide redox switch. We found that the first gene (mshA) in the biosynthetic pathway for MSH and the gene for amidase (mca) that participates in detoxifying mycothiol-reactive drugs are under direct control of s R . The s R target genes are induced not only by a thiol oxidant diamide, but also by alkylating agents that cause a rapid decrease in MSH. Expression of the s R regulon was also elevated in MSH-deficient mutants, suggesting that a decrease in the level of MSH is a natural intracellular trigger for s R activation. We found that MSH was capable of reducing RsrA to bind s R , whereas glutathione was not. These results support a proposal that the RsrA-s R system senses the intracellular level of reduced MSH, and that MSH serves as a natural modulator of the transcription system for its own replenishment in addition to being a redox buffer and drug detoxifier.

Biosynthesis and Functions of Mycothiol, the Unique Protective Thiol of Actinobacteria

“…When MSH levels were examined in a R -deficient mutant, they were fourfold lower than parental levels during all phases of growth. More recently, the role of R in MSH metabolism was elaborated by Park and Roe (106). A complex is formed between R and the reduced form of the R regulator.…”

“…R activates direct expression of a host of genes, including mshA and mca, and indirect expression of mshB, mshC, and mshD (106). Treatment of cells with reagents that deplete MSH, including the thiol oxidant diamide and the thiol alkylating agents monobromobimane (mBBr) and N-ethylmaleimide, leads to oxidation of RsrA and the release of R , with subsequent expression of the R regulon.…”

Regulation of Bacillus subtilis bacillithiol biosynthesis operons by Spx

“…In its reduced state, an anti-s R , RsrA, will sequester the sigma factor and prevent its interaction with the RNA polymerase. Under conditions of thiol stress, two cysteine residues in the RsrA will be oxidized, causing the dissociation of the s R , which will induce its regulon including the mshA gene (Park & Roe, 2008). Moreover, it was shown that MSH is the biological reductant that modulates RsrA activity, suggesting that the RsrA-s R system is a sensor for MSH levels in the cell (Park & Roe, 2008).…”

“…The induction of BSH biosynthesis genes is analogous to the stress-responsive induction of MSH synthesis in the actinomycetes. MSH production in Streptomyces coelicolor is under the regulation of the general stress sigma factor, s B (Lee et al, 2005) and the thiol-oxidative stress responsive sigma factor, s R (Park & Roe, 2008). In its reduced state, an anti-s R , RsrA, will sequester the sigma factor and prevent its interaction with the RNA polymerase.…”

“…Under conditions of thiol stress, two cysteine residues in the RsrA will be oxidized, causing the dissociation of the s R , which will induce its regulon including the mshA gene (Park & Roe, 2008). Moreover, it was shown that MSH is the biological reductant that modulates RsrA activity, suggesting that the RsrA-s R system is a sensor for MSH levels in the cell (Park & Roe, 2008). Our results suggest that in the Bacilli, Spx functions as the thiol stress sensor analogous to the RsrAs R system to upregulated LMW thiol synthesis.…”