Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.5.1.4 (deaminase)
 5,113 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Porcine calpains (Ca2+-dependent cysteine proteinases) I and II, which had been purified each to a homogeneous state, were found to hydrolyze specifically carboxyl-terminal amide of substance P and several other biologically active peptidyl amides. This amidase-like activity was demonstrated both by determining released ammonia and by separating products on high-performance liquid chromatography followed by amino acid analysis. The calpain-catalyzed deamidation of substance P occurred exclusively at the carboxyl-terminal amide, leaving the side-chain glutamine intact. Enkepharinamide and MSH-release inhibiting factor were scarcely deamidated. Calpains I and II showed similar specificities for these amide substances and similar profiles of inhibitions by various protease inhibitors, but distinctly different Ca2+ requirements. The specificity constants, kcat/Km, for substance P were found to be three to four orders of magnitude higher than those for the synthetic substrates.
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PMID:Amidase-like activity of calpain I and calpain II on substance P and its related peptides. 241 62

Mycothiol, 1-D-myo-inosityl-2-(N-acetylcysteinyl)amido-2-deoxy-alpha-D-glucopyranoside (MSH), is composed of N-acetylcysteine (AcCys) amide linked to 1-D-myo-inosityl-2-amino-2-deoxy-alpha-D-glucopyranoside (GlcN-Ins) and is the major thiol produced by most actinomycetes. When Mycobacterium smegmatis was treated with the alkylating agent monobromobimane (mBBr), the cellular mycothiol was converted to its bimane derivative (MSmB). The latter was rapidly cleaved to produce GlcN-Ins and the bimane derivative of N-acetylcysteine (AcCySmB), a mercapturic acid that was rapidly exported from the cells into the medium. The other product of cleavage, GlcN-Ins, was retained in the cell and utilized in the resynthesis of mycothiol. The mycothiol S-conjugate amidase (amidase) responsible for cleaving MSmB was purified to homogeneity from M. smegmatis. A value of K(m) = 95 +/- 8 microM and a value of k(cat) = 8 s(-)(1) was determined for the amidase with MSmB as substrate. Activity with 100 microM mycothiol or with the monobromobimane derivative of 1-D-myo-inosityl-2-(L-cysteinyl)amido-2-deoxy-alpha-D-glucopyra nos ide (CySmB-GlcN-Ins) or of 2-(N-acetyl-L-cysteinyl)amido-2-deoxy-(alpha, beta)-D-glucopyranoside (AcCySmB-GlcN) was at least 10(3) lower than with 100 microM MSmB, demonstrating that the amidase is highly specific for S-conjugates of mycothiol. Conjugates of mycothiol with the antibiotic cerulenin, N-ethylmaleimide, 3-(N-maleimidopropionyl)-biocytin, and 7-diethylamino-3-(4'-maleimidylphenyl)-4-methylcoumarin also exhibited significant activity. The sequence of the amino-terminal 20 residues was determined, and an open reading frame (Rv1082) coding for 288 residues having an identical predicted amino-terminal amino acid sequence was identified in the Mycobacterium tuberculosis genome. The Rv1082 gene (mca) from M. tuberculosis was cloned and expressed in Escherichia coli, and the expressed protein was shown to have substrate specificity similar to the amidase from M. smegmatis. These results indicate that mycothiol and mycothiol S-conjugate amidase play an important role in the detoxification of alkylating agents and antibiotics.
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PMID:A novel mycothiol-dependent detoxification pathway in mycobacteria involving mycothiol S-conjugate amidase. 1097 58

Mycothiol (MSH) is a novel thiol comprised of N-acetylcysteine amide-linked to GlcN-alpha(1-1)-Ins. It is the major thiol in most actinomycetes and is produced at millimolar levels in mycobacteria and streptomycetes. MSH biosynthesis occurs by linkage of GlcNAc to Ins, deacetylation to GlcN-Ins, ligation of the latter to L-cysteine, and transacetylation of the cysteinyl residue by CoASAc to produce MSH. The genes encoding the respective enzymes have been designated mshA, mshB, mshC, and mshD; all but mshA have been identified. Mycobacterium smegmatis mutants deficient in mshA, mshC, and mshD have been characterized. MSH plays a significant role in the detoxification of thiol-reactive substances, including formaldehyde, various electrophiles, and antibiotics. Mycothiol S-conjugates derived from electrophiles and antibiotics are cleaved by mycothiol S-conjugate amidase to release GlcN-Ins, used to resynthesize MSH, and a mercapturic acid which is excreted from the cell. A mycothiol-disulfide-selective reductase has been identified and likely helps to maintain cellular MSH in the reduced state. Mycothiol biochemistry has characteristics similar to those of glutathione but also has a variety of unique features.
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PMID:Mycothiol biochemistry. 1242 Jan 57

Mycothiol (1-D-myo-inosityl 2-(N-acetyl-L-cysteinyl)amido-2-deoxy-alpha-D-glucopyranoside, MSH or AcCys-GlcN-inositol (Ins)) is the major reducing agent in actinomycetes, including Mycobacterium tuberculosis. The biosynthesis of MSH involves a deacetylase that removes the acetyl group from the precursor GlcNAc-Ins to yield GlcN-Ins. The deacetylase (MshB) corresponds to Rv1170 of M. tuberculosis with a molecular mass of 33,400 Da. MshB is a Zn2+ metalloprotein, and the deacetylase activity is completely dependent on the presence of a divalent metal cation. We have determined the x-ray crystallographic structure of MshB, which reveals a protein that folds in a manner resembling lactate dehydrogenase in the N-terminal domain and a C-terminal domain consisting of two beta-sheets and two alpha-helices. The zinc binding site is in the N-terminal domain occupying a position equivalent to that of the NAD+ co-factor of lactate dehydrogenase. The Zn2+ is 5 coordinate with 3 residues from MshB (His-13, Asp-16, His-147) and two water molecules. One water would be displaced upon binding of substrate (GlcNAc-Ins); the other is proposed as the nucleophilic water assisted by the general base carboxylate of Asp-15. In addition to the Zn2+ providing electrophilic assistance in the hydrolysis, His-144 imidazole could form a hydrogen bond to the oxyanion of the tetrahedral intermediate. The extensive sequence identity of MshB, the deacetylase, with mycothiol S-conjugate amidase, an amide hydrolase that mediates detoxification of mycothiol S-conjugate xenobiotics, has allowed us to construct a faithful model of the catalytic domain of mycothiol S-conjugate amidase based on the structure of MshB.
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PMID:The crystal structure of 1-D-myo-inosityl 2-acetamido-2-deoxy-alpha-D-glucopyranoside deacetylase (MshB) from Mycobacterium tuberculosis reveals a zinc hydrolase with a lactate dehydrogenase fold. 1295 17

Mycothiol (MSH) is the major cellular thiol in Mycobacterium tuberculosis (M.tb). We hypothesize that the mycothiol-dependent detoxification pathway may serve an important role during oxygen stress management in M. tuberculosis, derived from normal aerobic metabolism, the macrophage environment and through the action of anti-tubercular antibiotics, such as Isoniazid (INH). Total mRNA and DNA were isolated from M. bovis BCG at different stages of growth in 7H9 mycobacterial medium. Three genes involved in mycothiol metabolism and encoding the enzymes mycothiol S-conjugate amidase (Mca, Rv1082), NADPH dependent mycothiol reductase (mtr, Rv2855), and N-Acetyl-1-D-myo-Inosityl-2-Amino-2-Deoxy-alpha-D-Glucopyranoside Deacetylase (GlcNAc-Ins deacetylase, Rv1170 or mshB) were investigated for genomic rearrangements and expression. The results show that the genomic domains of the genes remain conserved in evolutionary diverse and unrelated M. tuberculosis isolates. The genes encoding enzymes implicated in mycothiol reduction, mtr (Rv2855) and the mycothiol-dependant detoxification of electrophilic agents, Mca (Rv1082), are shown to be actively transcribed during logarithmic M. bovis BCG growth. The gene encoding GlcNAc-Ins deacetylase (the rate limiting mycothiol biosynthesis step) shows induction in the presence of INH. Antisense oligonucleotides to both GlcNAc-Ins deacetylase (Rv1170) and mtr (Rv2855) mRNA affect mycobacterial growth. In conclusion the results presented here suggest that these enzymes are sensitive to free radical generating antituberculosis drugs and may be useful targets for new drug development.
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PMID:Differential expression of mycothiol pathway genes: are they affected by antituberculosis drugs? 1518 46

Mycothiol (MSH), a functional analogue of glutathione (GSH) that is found exclusively in actinomycetes, reacts with electrophiles and toxins to form MSH-toxin conjugates. Mycothiol S-conjugate amidase (Mca) then catalyzes the hydrolysis of an amide bond in the S conjugates, producing a mercapturic acid of the toxin, which is excreted from the bacterium, and glucosaminyl inositol, which is recycled back to MSH. In this study, we have generated and characterized an allelic exchange mutant of the mca gene of Mycobacterium smegmatis. The mca mutant accumulates the S conjugates of the thiol-specific alkylating agent monobromobimane and the antibiotic rifamycin S. Introduction of M. tuberculosis mca epichromosomally or introduction of M. smegmatis mca integratively resulted in complementation of Mca activity and reduced levels of S conjugates. The mutation in mca renders the mutant strain more susceptible to electrophilic toxins, such as N-ethylmalemide, iodoacetamide, and chlorodinitrobenzene, and to several oxidants, such as menadione and plumbagin. Additionally we have shown that the mca mutant is also more susceptible to the antituberculous antibiotic streptomycin. Mutants disrupted in genes belonging to MSH biosynthesis are also more susceptible to streptomycin, providing further evidence that Mca detoxifies streptomycin in the mycobacterial cell in an MSH-dependent manner.
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PMID:Targeted mutagenesis of the Mycobacterium smegmatis mca gene, encoding a mycothiol-dependent detoxification protein. 1534 74

Mycothiol (MSH, AcCys-GlcN-Ins) is the major low molecular weight thiol in actinomycetes and is essential for growth of Mycobacterium tuberculosis. MshB, the GlcNAc-Ins deacetylase, is a key enzyme in MSH biosynthesis. MshB from M. tuberculosis was cloned, expressed, purified, and its properties characterized. Values of k(cat) and K(m) for MshB were determined for the biological substrate, GlcNAc-Ins, and several other good substrates. The substrate specificity of MshB was compared to that of M. tuberculosis mycothiol S-conjugate amidase (Mca), a homologous enzyme having weak GlcNAc-Ins deacetylase activity. Both enzymes are metalloamidases with overlapping amidase activity toward mycothiol S-conjugates (AcCySR-GlcN-Ins). The Ins residue and hydrophobic R groups enhance the activity with both MshB and Mca, but changes in the acyl group attached to GlcN have opposite effects on the two enzymes.
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PMID:Purification and characterization of Mycobacterium tuberculosis 1D-myo-inosityl-2-acetamido-2-deoxy-alpha-D-glucopyranoside deacetylase, MshB, a mycothiol biosynthetic enzyme. 1663 Jul 24

Mycothiol (MSH) is the major thiol in Actinobacteria and plays a role analogous to that of glutathione. The biosynthetic pathway has been established in mycobacteria and is initiated by the glycosyltransferase MshA. A key mycothiol-dependent detoxification pathway utilizes the amidase (Mca) to cleave mycothiol S-conjugates to produce GlcN-Ins and a mercapturic acid excreted from the cell. How expression of mycothiol genes is regulated in mycobacteria has been unclear so the report in this issue by Park and Roe showing that in Streptomyces coelicolor the redox controlled anti-sigma factor RsrA that binds the regulator sigma(R) controls key elements of mycothiol metabolism is a major advance. Conditions that deplete thiols are shown to induce directly expression of sigR, rsrA, mshA and mca, as well as the thioredoxin reductase-thioredoxin system, generating an autoregulatory cycle that persists until the thiol-depleting condition is alleviated. Evidence for indirect induction of mshB-D to support mycothiol biosynthesis is also presented. It was shown in vitro that mycothiol, like reduced thioredoxin and dithiothreitol, can reduce oxidized RsrA to activate its binding to sigma(R). These studies establish for the first time how mycothiol metabolism is regulated to cope with stress from thiol reactive toxins.
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PMID:Regulation of mycothiol metabolism by sigma(R) and the thiol redox sensor anti-sigma factor RsrA. 1843 82

Mycothiol (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 sigma(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 sigma(R). The sigma(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 sigma(R) regulon was also elevated in MSH-deficient mutants, suggesting that a decrease in the level of MSH is a natural intracellular trigger for sigma(R) activation. We found that MSH was capable of reducing RsrA to bind sigma(R), whereas glutathione was not. These results support a proposal that the RsrA-sigma(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.
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PMID:Mycothiol regulates and is regulated by a thiol-specific antisigma factor RsrA and sigma(R) in Streptomyces coelicolor. 1843 78

Marine actinomycetes have generated much recent interest as a potentially valuable source of novel antibiotics. Like terrestrial actinomycetes the marine actinomycetes are shown here to produce mycothiol as their protective thiol. However, a novel thiol, U25, was produced by MAR2 strain CNQ703 upon progression into stationary phase when secondary metabolite production occurred and became the dominant thiol. MSH and U25 were maintained in a reduced state during early stationary phase, but become significantly oxidized after 10 days in culture. Isolation and structural analysis of the monobromobimane derivative identified U25 as a homolog of mycothiol in which the acetyl group attached to the nitrogen of cysteine is replaced by a propionyl residue. This N-propionyl-desacetyl-mycothiol was present in 13 of the 17 strains of marine actinomycetes examined, including five strains of Salinispora and representatives of the MAR2, MAR3, MAR4 and MAR6 groups. Mycothiol and its precursor, the pseudodisaccharide 1-O-(2-amino-2-deoxy-alpha-D-glucopyranosyl)-D-myo-inositol, were found in all strains. High levels of mycothiol S-conjugate amidase activity, a key enzyme in mycothiol-dependent detoxification, were found in most strains. The results demonstrate that major thiol/disulfide changes accompany secondary metabolite production and suggest that mycothiol-dependent detoxification is important at this developmental stage.
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PMID:An N-acyl homolog of mycothiol is produced in marine actinomycetes. 1862 74


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