Redox processes play an important role in the physiology of M. tuberculosis. Since, M. tuberculosis spend substantial amount of time in the phagosomal milieu of host macrophages, it is believed that modulation of the redox reactions might help M. tuberculosis survive the hostile environment therein. We are interested in the structure and biochemical characterization of redox reactions in M.tuberculosis, with the hope that this will offer useful insights into the natural resistance of Mycobacteria towards oxidative killing. Towards achieving this objective, we have undertaken analysis of M. tuberculosis thioredoxins, alkylhydroperoxidase and inositol-1-phosphate synthase.
The thioredoxin system in prokaryotes consists of thioredoxins, thioredoxin reductase and NADPH. Using electrons from the cellular pool of NADPH, the thioredoxins act as the major reductants of cellular substrates, transferring electrons via the thioredoxin reductase. The other major redox buffer in prokaryotes is glutathione, which is absent in M. tuberculosis. However, M. tuberculosis possess equivalent mycothiol system, which might buffer redox equilibria. According to the originally annotated genome sequence, there are three thioredoxins and one thioredoxin reductase present in M. tuberculosis. Our characterization has revealed that atleast one of the three thioredoxins is a pseudo gene, while the redox potential of the other two thioredoxins is slightly lower than their E. coli homologues.
The only gene that appears to be induced by peroxides in M. tuberculosis is the katG gene encoding the catalase peroxidase. This is because of the canonical regulator of oxidative stress-oxyR appears to be mutated in M. tuberculosis. In the isoniazid resistant bacilli, the katG gene accumulates mutations, thereby potentially rendering oxidative response ineffective. In these bacilli, the ahpC gene has been observed to be overexpressed. Our characterization of AhpC has revealed that it undergoes interesting conformational and quaternary structural changes during catalysis. It appears to shuttle between dimeric and decameric states during reaction cycle. The dimers within the decamers are held together by ionic forces.
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Conformational flexibility of M. tuberculosis Thioredoxin reductase: Crystal Structure and Normal Mode Analysis (PDF)
Mohd. Akif, K. Suhre, C. Verma and S. C. Mande
Acta crystallogr. (2005) D61, 1603- 1611.
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Expression, purification, crystallization and preliminary X-ray crystallographic studies of Mycobacterium tuberculosis thioredoxin reductase (PDF)
Mohd. Akif, R. Chauhan and S. C. Mande
Acta Crystallogr D (2004) 60, 777-779
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Site directed mutagenesis reveals a novel catalytic mechanism of Mycobacterium tuberculosis Alkylhydroperoxidase C (PDF)
R. Chauhan and S. C. Mande
Biochem J. (2002) 367, 255- 261.
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Characterization of the Mycobacterium tuberculosis H37Rv alkyl hydroperoxidase AhpC points to the importance of ionic interactions in oligomerization and activity (PDF)
R. Chauhan and S. C. Mande
Biochem J. (2001) 354, 209- 215.
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Complex evolution of the inositol-1-phosphate synthase gene among archaea and eubacteria (PDF)
N. Bachhawat and S. C. Mande
Trends Genet. (2000) 16, 111- 113.
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Identification of the ino1 gene of Mycobacterium tuberculosis H37Rv reveals a novel class of inositol-1-phosphate synthase enzyme (PDF)
N. Bachhawat and S. C. Mande.
J. Mol. Biol. (1999) 291, 531-536.
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