Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0026918 (Mycobacterium)
 52,428 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rifampin resistance in respiratory isolates of Mycobacterium tuberculosis from Mozambique was detected by screening for point mutations using polymerase chain reaction (PCR) and DNA sequence analysis. The target template was a 350-bp fragment of rpoB encoding the beta-subunit of the RNA polymerase. Of the 66 strains studied, 38 were rifampin resistant by susceptibility testing with the radiometric method, 3 were intermediately resistant, and 25 were susceptible to rifampin. In 39 of the 41 rifampin-resistant strains, base-substitutions in the rpoB fragment were detected, and a total of 13 distinct mutations affecting 6 amino acids were observed. One of these mutations (His-->Thr in amino acid 526) was not previously described. The isolates were also investigated by restriction fragment length polymorphism (RFLP) analysis using the insertion element IS6110 as a hybridization probe. A total of 47 RFLP patterns were identified, with up to 9 isolates having the same RFLP pattern. Strains with the same RFLP pattern harbored different mutations in rpoB, suggesting that acquisition of rifampin resistance followed the spread of a rifampin-susceptible clone. The data showed that rifampin resistance can be detected with a high sensitivity by DNA sequence analysis of this fragment of rpoB. However, a few strains with rifampin resistance due to factors other than base substitutions in rpoB could be missed.
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PMID:Detection of rifampin resistance among isolates of Mycobacterium tuberculosis from Mozambique. 915 3

Glycine 99 in L-lactate monooxygenase (LMO) from Mycobacterium smegmatis was mutated to serine and threonine, and the resultant mutants were studied extensively to explore the role of this residue in maintaining monooxygenase activity and in controlling the reactivity with molecular oxygen. Both mutants were observed to lose monooxygenase activity completely and generate H2O2 and pyruvate as reaction products. However, the mutants have much lower activities than a true L-lactate oxidase. The oxygen reactivities of the reduced and semiquinone forms of the mutant enzymes were significantly different from those of wild type enzyme. These results confirm our previous suggestion that the electronic interactions in the active site are a crucial factor that governs the oxygen reactivity of the enzyme (Sun, W., Williams, C. H., Jr., and Massey, V. (1996) J. Biol. Chem. 271, 17226-17233). In addition, the mutants cause a dramatic decrease of the rate of flavin reduction by L-lactate compared with the wild type enzyme, mainly due to the much lower stabilization of the transition state.
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PMID:The role of glycine 99 in L-lactate monooxygenase from Mycobacterium smegmatis. 934 Nov 46

We have charterized a Mycobacterium smegmatis gene encoding a homolog of the ATP-dependent protease Lon (La). Our identification of a Lon homolog, in conjunction with our previous work, identifies M. smegmatis as the first known example of a eubacterium containing both Lon and a complete 20S proteasome (containing both alpha- and beta-subunits). Despite the significant primary sequence divergence between M. smegmatis Lon (Ms-Lon) and E. coli Lon (Ec-Lon), expression of Ms-Lon was only moderately toxic to E. coli cells. The ability of E. coli cells to tolerate expression of Ms-Lon reveals that Ms-Lon does not recognize and degrade essential E. coli proteins. We conclude that discrimination against nonsubstrate proteins is broadly conserved between Ec-Lon and Ms-Lon. Additional conservation of substrate recognition was demonstrated by the ability of Ms-Lon to degrade efficiently RcsA, a natural substrate of Ec-Lon. Purified Ms-Lon displays chymotrypsin-like specificity in peptidase assays that are stimulated by unfolded protein and supported by nonhydrolyzed nucleotide analogs. Maximal peptidase activity requires ATP or dATP. Replacement of Ms-Lon's catalytic Ser with Ala (S675A), Thr (S675T), or Cys (S675C) reduced to background levels Ms-Lon's in vitro peptidase activity. However, by employing a sensitive in vivo assay, based on the degradation of RcsA, we demonstrated that the S675C variant retained specific protease activity. Finally, variants of Ms-Lon, with substututions at or near S675, reduce the enzyme's basal ATPase activity, suggesting a structural interaction between the peptidase and ATPase active sites of Ms-Lon.
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PMID:The lon protease from Mycobacterium smegmatis: molecular cloning, sequence analysis, functional expression, and enzymatic characterization. 942 59

Several genes from prokaryotes and lower eukaryotes have been found to contain an in-frame open reading frame, which encodes for an internal protein (intein). Post-translationally, the internal polypeptide auto-splices and ligates the external sequences to yield a functional external protein (extein) and an intein. Most, but not all inteins, contain, apart from a splicing domain, a separate endonucleolytic domain that enables them to maintain their presence by a homing mechanism. We report here the crystal structure of an intein found in the gyrase A subunit from Mycobacterium xenopi at 2.2 A resolution. The structure contains an unusual beta-fold with the catalytic splice junctions at the ends of two adjacent antiparallel beta-strands. The arrangement of the active site residues Ser 1, Thr 72, His 75, His 197, and Asn 198 is consistent with a four-step mechanism for the cleavage-ligation reaction. Using site-directed mutagenesis, the N-terminal cysteine, proposed as the nucleophile in the first step of the splicing reaction, was changed to a Ser 1 and Ala 0, thus capturing the intein in a pre-spliced state.
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PMID:Crystal structure of GyrA intein from Mycobacterium xenopi reveals structural basis of protein splicing. 943 16

The characteristic lipids and specific surface antigens which typify serotypes of Mycobacterium avium-intracellulare complex (MAC) serogroup have been examined. The characteristic lipids are recognized as glycopeptidolipid (GPL) antigen consisted of short-chain acylated oligosaccharides linked to long-chain fatty acyl-D-Phe-D-allo Thr-D-Ala-L-alaninol-O-3, 4-di-O-methyl rhamnose 'core'. The lack of information on the properties of GPL antigen from serovar 16 and a large number of patients infected with MAC serovar 16 have prompted an examination of the chemical structures utilizing the analytical techniques of alditol acetates with GC or GC/MS, and making use of FAB/MS and 1H-NMR to analyze the intact GPLs. The following structure of serovar 16 GPL antigen was proposed with molecular weight: 1933, main fatty acyl component: OH-C32:0, and oligosaccharides: 3-amido (2'-methyl, 3'-hydroxy, 4'-methoxy pentanoyl) 3, 6-dideoxy hexose-->4-O-methyl-L-rhamnose-->L-rhamnose-->L-rhamnose-->6-deoxy-L-talose The unique structure may be an important factor in physiological and pathological roles. The GPL antigens were highly reactive in ELISA against sera from rabbits hyperimmunized with MAC strains, indicating its basic antigenicity. The type-specific antigen of serovar 16 was also specifically reactive against sera from patients infected with MAC serovar 16, but invariant core was not. Apparently, the epitope of GPL antigen of serovar 16 was specific oligosaccharides, 3-amido (2'-methyl, 3'-hydroxy, 4'-methoxy pentanoyl) 3, 6-dideoxy hexose. It was found that the ELISA using GPL antigens was particularly useful for the serovar diagnosis of human infections with MAC.
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PMID:[Structure and antigenicity of the glycopeptidolipid antigen of Mycobacterium avium-intracellulare complex (MAC) serovar 16]. 961 50

We have examined the functional properties including autophosphorylation of the Mycobacterium leprae Hsp70 homologue. Recombinant M. leprae Hsp70 had pH optima for its adenosine triphosphatase and autophosphorylating activities which were near pH 8 and 6, respectively. Both these activities were inhibited by reduced and alkylated bovine pancreatic trypsin inhibitor, but not other tested substrates. Autophosphorylation was augmented by up to 25 mM Ca2+. Using site-directed mutagenesis to construct two Thr-->Ala mutants at positions 175 and 193, and phosphoamino acid analysis, it was shown that Thr175 was the dominant threonine residue autophosphorylated in M. leprae Hsp70. Phosphorylation led to an increased affinity for a model polypeptide substrate, reduced and alkylated bovine albumin. These properties are compared with those of the DnaK protein of Escherichia coli.
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PMID:Phosphorylation of Mycobacterium leprae heat-shock 70 protein at threonine 175 alters its substrate binding characteristics. 974 55

A series of mutants bearing single amino acid substitutions often encountered in the catalase/peroxidase, KatG, from isoniazid-resistant isolates of Mycobacterium tuberculosis has been produced by site-directed mutagenesis. The resultant enzymes were overexpressed, purified and characterized. Replacing Cys-20 by Ser abolished disulphide-bridge formation, but did not affect either dimerization of the enzyme or catalysis. The substitution of Thr-275, which is probably involved in electron transfer from the haem, by proline resulted in a highly unstable enzyme with insignificant enzyme activities. The most commonly occurring substitution in drug-resistant clinical isolates is the replacement of Ser-315 by Thr; this lowered catalase and peroxidase activities by 50% and caused a significant decrease in the KatG-mediated inhibition of the activity of the NADH-dependent enoyl-[acyl-carrier protein] reductase, InhA, in vitro. The ability of this enzyme to produce free radicals from isoniazid was severely impaired, as judged by its loss of NitroBlue Tetrazolium reduction activity. Replacement of Leu-587 by Pro resulted in marked instability of KatG, indicating that the C-terminal domain is also important for structural and functional integrity.
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PMID:Use of site-directed mutagenesis to probe the structure, function and isoniazid activation of the catalase/peroxidase, KatG, from Mycobacterium tuberculosis. 1005 49

Homoserine kinase, the product of the thrB gene, catalyses an obligatory step of threonine biosynthesis. In Pseudomonas aeruginosa, unlike Escherichia coli, inactivation of the previously identified thrB gene does not result in threonine auxotrophy. A new gene, named thrH, was isolated that, when expressed in E. coli thrB mutant strains, results in complementation of the mutant phenotype. In P. aeruginosa, threonine auxotrophy is observed only when both thrB and thrH are simultaneously inactivated. Thus, thrH encodes a protein with an in vivo homoserine-kinase-like activity. Surprisingly, thrH overexpression allows complementation of serine auxotrophy of E. coli and P. aeruginosa serB mutants. These mutants are affected in the phosphoserine phosphatase protein, an enzyme involved in serine biosynthesis. Comparison analysis revealed sequence homology between ThrH and the SerB proteins from different organisms. This could explain the in vivo phosphoserine phosphatase activity of ThrH when overproduced. ThrH differs from the protein encoded by the serB gene which was identified in P. aeruginosa. Thus, two SerB-like proteins co-exist in P. aeruginosa, a situation also found in Mycobacterium tuberculosis.
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PMID:ThrH, a homoserine kinase isozyme with in vivo phosphoserine phosphatase activity in Pseudomonas aeruginosa. 1022 Jan 64

The Mycobacterium tuberculosis complex includes M. tuberculosis, M. bovis, M. africanum, and M. microti. Most clinical isolates are M. tuberculosis or M. bovis. These species can be distinguished by phenotypes and genotypes. However, there is no simple definition of M. africanum, and some authors question the validity of this species. We analyzed 17 human isolates from Sierra Leone, identified as M. africanum by biochemical and growth characteristics. We sequenced polymorphic genes and intergenic regions. We amplified DNA from six loci with variable numbers of tandem repeats (VNTRs) and determined the exact number of repeats at each locus in each strain. All M. africanum isolates had the ancestral CTG Leu at katG codon 463. Drug-resistant M. africanum isolates had katG and rpoB mutations similar to those found in drug-resistant M. bovis and M. tuberculosis. Fourteen Sierra Leone M. africanum isolates (designated group A) had katG codon 203 ACC Thr, also found in M. africanumT (the T indicates type strain) from Senegal. Group A isolates clustered with M. africanumT by VNTR analysis. Three M. africanum isolates (group B) had katG codon 203 ACT Thr, found in M. tuberculosisT, and clustered with M. tuberculosisT by VNTR analysis. Phenotypic identification of M. africanum yielded a heterogeneous collection of strains. Genotypic analyses identified a cluster (M. africanum group A) which included M. africanumT and was distinct from the rest of the M. tuberculosis complex. Future studies of M. africanum should include both phenotypic and genotypic analyses.
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PMID:Phenotypic and genotypic characterization of Mycobacterium africanum isolates from West Africa. 1032 47

PknB is a member of the newly discovered eukaryotic-like protein serine/threonine kinase (PSTK) family of proteins. The pknB gene was cloned and expressed in Escherichia coli. The active recombinant protein was purified and shown to be reactive with antiphosphoserine antibodies, as well as with antibodies to the phosphorylated eukaryotic Ser/Thr kinases mitogen-activated protein kinase kinase 3 and 6, P38, and Creb. In vitro kinase assays demonstrated that PknB is a functional kinase that is autophosphorylated on serine/threonine residues and is also able to phosphorylate the peptide substrate myelin basic protein. Analysis of pknB expression in Mycobacterium tuberculosis indicates the presence of pknB mRNA in (i) organisms grown in vitro in bacteriological media, (ii) a murine macrophage in vitro infection model, and (iii) in vivo alveolar macrophages from a patient with tuberculosis.
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PMID:Expression and characterization of the Mycobacterium tuberculosis serine/threonine protein kinase PknB. 1053 Dec 15


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