Accepted name: S-(hydroxymethyl)mycothiol dehydrogenase
Reaction: S-(hydroxymethyl)mycothiol + NAD+ = S-formylmycothiol + NADH + H+
Glossary: mycothiol = 1-O-[2-(N2-acetyl-L-cysteinamido)-2-deoxy-α-D-glucopyranosyl]-1D-myo-inositol
Other name(s): NAD/factor-dependent formaldehyde dehydrogenase; mycothiol-dependent formaldehyde dehydrogenase
Systematic name: S-(hydroxymethyl)mycothiol:NAD+ oxidoreductase
Comments: S-hydroxymethylmycothiol is believed to form spontaneously from formaldehyde and mycothiol. This enzyme oxidizes the product of this spontaneous reaction to S-formylmycothiol, in a reaction that is analogous to EC, S-(hydroxymethyl)glutathione dehydrogenase.
1.  Misset-Smits, M., Van Ophem, P.W., Sakuda, S. and Duine, J.A. Mycothiol, 1-O-(2′-[N-acetyl-L-cysteinyl]amido-2′-deoxy-α-D-glucopyranosyl)-D-myo-inositol, is the factor of NAD/factor-dependent formaldehyde dehydrogenase. FEBS Lett. 409 (1997) 221–222. [PMID: 9202149]
2.  Norin, A., Van Ophem, P.W., Piersma, S.R., Person, B., Duine, J.A. and Jornvall, H. Mycothiol-dependent formaldehyde dehydrogenase, a prokaryotic medium-chain dehydrogenase/reductase, phylogenetically links different eukaryotic alcohol dehydrogenase's - primary structure, conformational modelling and functional correlations. Eur. J. Biochem. 248 (1997) 282–289. [PMID: 9346279]
3.  Vogt, R.N., Steenkamp, D.J., Zheng, R. and Blanchard, J.S. The metabolism of nitrosothiols in the Mycobacteria: identification and characterization of S-nitrosomycothiol reductase. Biochem. J. 374 (2003) 657–666. [PMID: 12809551]
4.  Rawat, M. and Av-Gay, Y. Mycothiol-dependent proteins in actinomycetes. FEMS Microbiol. Rev. 31 (2007) 278–292. [PMID: 17286835]
[EC created 2010 as EC, transferred 2010 to EC]
Transferred entry: mycothiol-dependent formaldehyde dehydrogenase. Now EC, S-(hydroxymethyl)mycothiol dehydrogenase
[EC created 2000, deleted 2010]
Accepted name: mycothione reductase
Reaction: 2 mycothiol + NAD(P)+ = mycothione + NAD(P)H + H+
Glossary: mycothiol = 1-O-[2-(N2-acetyl-L-cysteinamido)-2-deoxy--D-glucopyranosyl]-1D-myo-inositol
mycothione = oxidized (disulfide) form of mycothiol
Other name(s): mycothiol-disulfide reductase
Systematic name: mycothiol:NAD(P)+ oxidoreductase
Comments: Contains FAD. No activity with glutathione, trypanothione or coenzyme A as substrate.
1.  Patel, M.P. and Blanchard, J.S. Expression, purification, and characterization of Mycobacterium tuberculosis mycothione reductase. Biochemistry 38 (1999) 11827–11833. [PMID: 10512639]
2.  Patel, M.P. and Blanchard, J.S. Mycobacterium tuberculosis mycothione reductase: pH dependence of the kinetic parameters and kinetic isotope effects. Biochemistry 40 (2001) 5119–5126. [PMID: 11318633]
[EC created 2002]
Accepted name: mycoredoxin-dependent peroxiredoxin
Reaction: mycoredoxin + ROOH = mycoredoxin disulfide + H2O + ROH
Other name(s): ahpE (gene name)
Systematic name: mycoredoxin:hydroperoxide oxidoreductase
Comments: Peroxiredoxins (Prxs) are a ubiquitous family of antioxidant proteins. They can be divided into three classes: typical 2-Cys, atypical 2-Cys and 1-Cys peroxiredoxins [1]. The peroxidase reaction comprises two steps centred around a redox-active cysteine called the peroxidatic cysteine. All three peroxiredoxin classes have the first step in common, in which the peroxidatic cysteine attacks the peroxide substrate and is oxidized to S-hydroxycysteine (a sulfenic acid) (see mechanism). The second step of the peroxidase reaction, the regeneration of cysteine from S-hydroxycysteine, distinguishes the three peroxiredoxin classes. For typical 2-Cys Prxs, in the second step, the peroxidatic S-hydroxycysteine from one subunit is attacked by the ‘resolving’ cysteine located in the C-terminus of the second subunit, to form an intersubunit disulfide bond, which is then reduced by one of several cell-specific thiol-containing reductants completing the catalytic cycle. In the atypical 2-Cys Prxs, both the peroxidatic cysteine and its resolving cysteine are in the same polypeptide, so their reaction forms an intrachain disulfide bond. The 1-Cys Prxs conserve only the peroxidatic cysteine, so its regeneration involves direct interaction with a reductant molecule. Mycoredoxin-dependent enzymes are found in Mycobacteria. Following the reduction of the substrate, the sulfenic acid derivative of the peroxidatic cysteine forms a protein mixed disulfide with the N-terminal cysteine of mycoredoxin, which is then reduced by the C-terminal cysteine of mycoredoxin, restoring the peroxiredoxin to active state and resulting in an intra-protein disulfide in mycoredoxin. The disulfide is eventually reduced by mycothiol.
1.  Wood, Z.A., Schröder, E., Harris, J.R. and Poole, L.B. Structure, mechanism and regulation of peroxiredoxins. Trends Biochem. Sci. 28 (2003) 32–40. [PMID: 12517450]
2.  Hugo, M., Turell, L., Manta, B., Botti, H., Monteiro, G., Netto, L.E., Alvarez, B., Radi, R. and Trujillo, M. Thiol and sulfenic acid oxidation of AhpE, the one-cysteine peroxiredoxin from Mycobacterium tuberculosis: kinetics, acidity constants, and conformational dynamics. Biochemistry 48 (2009) 9416–9426. [PMID: 19737009]
3.  Hugo, M., Van Laer, K., Reyes, A.M., Vertommen, D., Messens, J., Radi, R. and Trujillo, M. Mycothiol/mycoredoxin 1-dependent reduction of the peroxiredoxin AhpE from Mycobacterium tuberculosis. J. Biol. Chem. 289 (2014) 5228–5239. [PMID: 24379404]
4.  Kumar, A., Balakrishna, A.M., Nartey, W., Manimekalai, M.SS. and Gruber, G. Redox chemistry of Mycobacterium tuberculosis alkylhydroperoxide reductase E (AhpE): Structural and mechanistic insight into a mycoredoxin-1 independent reductive pathway of AhpE via mycothiol. Free Radic. Biol. Med. 97 (2016) 588–601. [PMID: 27417938]
5.  Pedre, B., van Bergen, L.A., Pallo, A., Rosado, L.A., Dufe, V.T., Molle, I.V., Wahni, K., Erdogan, H., Alonso, M., Proft, F.D. and Messens, J. The active site architecture in peroxiredoxins: a case study on Mycobacterium tuberculosis AhpE. Chem. Commun. (Camb.) 52 (2016) 10293–10296. [PMID: 27471753]
[EC created 1983 as EC, part transferred 2020 to EC]
Accepted name: mycoredoxin
Reaction: arseno-mycothiol + mycoredoxin = arsenite + mycothiol-mycoredoxin disulfide
Glossary: mycothiol = 1-O-[2-(N2-acetyl-L-cysteinamido)-2-deoxy-α-D-glucopyranosyl]-1D-myo-inositol
Other name(s): Mrx1; MrxI
Systematic name: arseno-mycothiol:mycoredoxin oxidoreductase
Comments: Reduction of arsenate is part of a defense mechanism of the cell against toxic arsenate. The substrate arseno-mycothiol is formed by EC (arsenate:mycothiol transferase). A second mycothiol recycles mycoredoxin and forms mycothione.
1.  Ordonez, E., Van Belle, K., Roos, G., De Galan, S., Letek, M., Gil, J.A., Wyns, L., Mateos, L.M. and Messens, J. Arsenate reductase, mycothiol, and mycoredoxin concert thiol/disulfide exchange. J. Biol. Chem. 284 (2009) 15107–15116. [PMID: 19286650]
[EC created 2010]
Accepted name: mycothiol synthase
Reaction: desacetylmycothiol + acetyl-CoA = CoA + mycothiol
Glossary: desacetylmycothiol = 1-O-[2-(L-cysteinamido)-2-deoxy-α-D-glucopyranosyl]-1D-myo-inositol
mycothiol = 1-O-[2-(N2-acetyl-L-cysteinamido)-2-deoxy-α-D-glucopyranosyl]-1D-myo-inositol
Other name(s): MshD
Systematic name: acetyl-CoA:desacetylmycothiol O-acetyltransferase
Comments: This enzyme catalyses the last step in the biosynthesis of mycothiol, the major thiol in most actinomycetes, including Mycobacterium [1]. The enzyme is a member of a large family of GCN5-related N-acetyltransferases (GNATs) [2]. The enzyme has been purified from Mycobacterium tuberculosis H37Rv. Acetyl-CoA is the preferred CoA thioester but propionyl-CoA is also a substrate [3].
1.  Spies, H.S. and Steenkamp, D.J. Thiols of intracellular pathogens. Identification of ovothiol A in Leishmania donovani and structural analysis of a novel thiol from Mycobacterium bovis. Eur. J. Biochem. 224 (1994) 203–213. [PMID: 8076641]
2.  Koledin, T., Newton, G.L. and Fahey, R.C. Identification of the mycothiol synthase gene (mshD) encoding the acetyltransferase producing mycothiol in actinomycetes. Arch. Microbiol. 178 (2002) 331–337. [PMID: 12375100]
3.  Vetting, M.W., Roderick, S.L., Yu, M. and Blanchard, J.S. Crystal structure of mycothiol synthase (Rv0819) from Mycobacterium tuberculosis shows structural homology to the GNAT family of N-acetyltransferases. Protein Sci. 12 (2003) 1954–1959. [PMID: 12930994]
[EC created 2010]
Accepted name: D-inositol-3-phosphate glycosyltransferase
Reaction: UDP-N-acetyl-α-D-glucosamine + 1D-myo-inositol 3-phosphate = 1-O-(2-acetamido-2-deoxy-α-D-glucopyranosyl)-1D-myo-inositol 3-phosphate + UDP
Glossary: mycothiol = 1-O-[2-(N2-acetyl-L-cysteinamido)-2-deoxy-α-D-glucopyranosyl]-1D-myo-inositol
Other name(s): mycothiol glycosyltransferases; MshA; UDP-N-acetyl-D-glucosamine:1D-myo-inositol 3-phosphate α-D-glycosyltransferase
Systematic name: UDP-N-acetyl-α-D-glucosamine:1D-myo-inositol 3-phosphate α-D-glycosyltransferase (configuration-retaining)
Comments: The enzyme, which belongs to the GT-B fold superfamily, catalyses the first dedicated reaction in the biosynthesis of mycothiol [1]. The substrate was initially believed to be inositol, but eventually shown to be D-myo-inositol 3-phosphate [2]. A substantial conformational change occurs upon UDP binding, which generates the binding site for D-myo-inositol 3-phosphate [3].
1.  Newton, G.L., Koledin, T., Gorovitz, B., Rawat, M., Fahey, R.C. and Av-Gay, Y. The glycosyltransferase gene encoding the enzyme catalyzing the first step of mycothiol biosynthesis (mshA). J. Bacteriol. 185 (2003) 3476–3479. [PMID: 12754249]
2.  Newton, G.L., Ta, P., Bzymek, K.P. and Fahey, R.C. Biochemistry of the initial steps of mycothiol biosynthesis. J. Biol. Chem. 281 (2006) 33910–33920. [PMID: 16940050]
3.  Vetting, M.W., Frantom, P.A. and Blanchard, J.S. Structural and enzymatic analysis of MshA from Corynebacterium glutamicum: substrate-assisted catalysis. J. Biol. Chem. 283 (2008) 15834–15844. [PMID: 18390549]
[EC created 2010]
Accepted name: arsenate-mycothiol transferase
Reaction: arsenate + mycothiol = arseno-mycothiol + H2O
Glossary: mycothiol = 1-O-[2-(N2-acetyl-L-cysteinamido)-2-deoxy--D-glucopyranosyl]-1D-myo-inositol
Other name(s): ArsC1; ArsC2; mycothiol:arsenate transferase
Systematic name: mycothiol:arsenate S-arsenotransferase
Comments: Reduction of arsenate is part of a defence mechanism of the cell against toxic arsenate. The product arseno-mycothiol is reduced by EC (mycoredoxin) to arsenite and mycothiol-mycoredoxin disulfide. Finally, a second mycothiol recycles mycoredoxin and forms mycothione.
1.  Ordonez, E., Van Belle, K., Roos, G., De Galan, S., Letek, M., Gil, J.A., Wyns, L., Mateos, L.M. and Messens, J. Arsenate reductase, mycothiol, and mycoredoxin concert thiol/disulfide exchange. J. Biol. Chem. 284 (2009) 15107–15116. [PMID: 19286650]
[EC created 2010]
Accepted name: N-acetyl-1-D-myo-inositol-2-amino-2-deoxy-α-D-glucopyranoside deacetylase
Reaction: 1-O-(2-acetamido-2-deoxy-α-D-glucopyranosyl)-1D-myo-inositol + H2O = 1-O-(2-amino-2-deoxy-α-D-glucopyranosyl)-1D-myo-inositol + acetate
Glossary: mycothiol = 1-O-[2-(N2-acetyl-L-cysteinamido)-2-deoxy-α-D-glucopyranosyl]-1D-myo-inositol
Other name(s): MshB
Systematic name: 1-(2-acetamido-2-deoxy-α-D-glucopyranosyl)-1D-myo-inositol acetylhydrolase
Comments: This enzyme is considered the key enzyme and rate limiting step in the mycothiol biosynthesis pathway [1]. In addition to acetylase activity, the enzyme possesses weak activity of EC, mycothiol S-conjugate amidase, and shares sequence similarity with that enzyme [2]. The enzyme requires a divalent transition metal ion for activity, believed to be Zn2+ [3].
1.  Rawat, M., Kovacevic, S., Billman-Jacobe, H. and Av-Gay, Y. Inactivation of mshB, a key gene in the mycothiol biosynthesis pathway in Mycobacterium smegmatis. Microbiology 149 (2003) 1341–1349. [PMID: 12724395]
2.  Newton, G.L., Av-Gay, Y. and Fahey, R.C. N-Acetyl-1-D-myo-inosityl-2-amino-2-deoxy-α-D-glucopyranoside deacetylase (MshB) is a key enzyme in mycothiol biosynthesis. J. Bacteriol. 182 (2000) 6958–6963. [PMID: 11092856]
3.  Maynes, J.T., Garen, C., Cherney, M.M., Newton, G., Arad, D., Av-Gay, Y., Fahey, R.C. and James, M.N. The crystal structure of 1-D-myo-inosityl 2-acetamido-2-deoxy-α-D-glucopyranoside deacetylase (MshB) from Mycobacterium tuberculosis reveals a zinc hydrolase with a lactate dehydrogenase fold. J. Biol. Chem. 278 (2003) 47166–47170. [PMID: 12958317]
[EC created 2010]
Accepted name: mycothiol S-conjugate amidase
Reaction: a mycothiol S-conjugate + H2O = an N-acetyl L-cysteine-S-conjugate + 1-O-(2-amino-2-deoxy-α-D-glucopyranosyl)-1D-myo-inositol
Glossary: mycothiol = 1-O-[2-(N2-acetyl-L-cysteinamido)-2-deoxy-α-D-glucopyranosyl]-1D-myo-inositol
N-acetyl L-cysteine-S-conjugate = mercapturic acid
Other name(s): MCA
Systematic name: mycothiol S-conjugate 1D-myo-inositol 2-amino-2-deoxy-α-D-glucopyranosyl-hydrolase
Comments: The enzyme that is found in actinomycetes is involved in the detoxification of oxidizing agents and electrophilic antibiotics. The enzyme has low activity with 1-O-(2-acetamido-2-deoxy-α-D-glucopyranosyl)-1D-myo-inositol as substrate (cf. EC, N-acetyl-1-D-myo-inositol-2-amino-2-deoxy-α-D-glucopyranoside deacetylase) [2].
1.  Newton, G.L., Av-Gay, Y. and Fahey, R.C. A novel mycothiol-dependent detoxification pathway in mycobacteria involving mycothiol S-conjugate amidase. Biochemistry 39 (2000) 10739–10746. [PMID: 10978158]
2.  Steffek, M., Newton, G.L., Av-Gay, Y. and Fahey, R.C. Characterization of Mycobacterium tuberculosis mycothiol S-conjugate amidase. Biochemistry 42 (2003) 12067–12076. [PMID: 14556638]
[EC created 2013]
Accepted name: L-cysteine:1D-myo-inositol 2-amino-2-deoxy-α-D-glucopyranoside ligase
Reaction: 1-O-(2-amino-2-deoxy-α-D-glucopyranosyl)-1D-myo-inositol + L-cysteine + ATP = 1-O-[2-(L-cysteinamido)-2-deoxy-α-D-glucopyranosyl]-1D-myo-inositol + AMP + diphosphate
Glossary: mycothiol = 1-O-[2-(N2-acetyl-L-cysteinamido)-2-deoxy--D-glucopyranosyl]-1D-myo-inositol
Other name(s): MshC; MshC ligase; Cys:GlcN-Ins ligase; mycothiol ligase
Systematic name: L-cysteine:1-O-(2-amino-2-deoxy-α-D-glucopyranosyl)-1D-myo-inositol ligase (AMP-forming)
Comments: This enzyme is a key enzyme in the biosynthesis of mycothiol, a small molecular weight thiol found in Mycobacteria spp. and other actinomycetes. Mycothiol plays a fundamental role in these organisms by helping to provide protection from the effects of reactive oxygen species and electrophiles, including many antibiotics. The enzyme may represent a novel target for new classes of antituberculars [2].
1.  Fan, F., Luxenburger, A., Painter, G.F. and Blanchard, J.S. Steady-state and pre-steady-state kinetic analysis of Mycobacterium smegmatis cysteine ligase (MshC). Biochemistry 46 (2007) 11421–11429. [PMID: 17848100]
2.  Gutierrez-Lugo, M.T., Newton, G.L., Fahey, R.C. and Bewley, C.A. Cloning, expression and rapid purification of active recombinant mycothiol ligase as B1 immunoglobulin binding domain of streptococcal protein G, glutathione-S-transferase and maltose binding protein fusion proteins in Mycobacterium smegmatis. Protein Expr. Purif. 50 (2006) 128–136. [PMID: 16908186]
3.  Tremblay, L.W., Fan, F., Vetting, M.W. and Blanchard, J.S. The 1.6 Å crystal structure of Mycobacterium smegmatis MshC: the penultimate enzyme in the mycothiol biosynthetic pathway. Biochemistry 47 (2008) 13326–13335. [PMID: 19053270]
[EC created 2009]