The superoxide dismutases (SODs) are a family of metalloproteins that catalyse the disproportionation of the toxic superoxide anion into hydrogen peroxide and oxygen. The iron-coordinating SOD of Mycobacterium tuberculosis is an ideal candidate for structure-function analysis by site-directed mutagenesis and X-ray crystallographic techniques. Comparison of the previously determined M. tuberculosis structure with other known SOD structures and mycobacterial SOD sequences highlighted candidate residues for mutagenesis to study their roles in areas of interest, both to the enzyme family and the intracellular survival of the bacterium, the causal agent of tuberculosis. Individual members of the SOD family are generally only active with either iron or manganese as the catalytic ion, despite high conservation of the active site. Histidine 145 was highlighted as a potential discriminating residue, with the residue being glutamine in the closely related M. leprae manganese-SOD. Mutation to glutamine did not alter the metal ion specificity, although mutation to glutamate produced a manganese-binding M. tuberculosis mutant. These findings suggest that the charge of the residue in this position plays a role in metal ion deternlination. The 88 kD tetramer is compact in nature, primarily due to novel dimer-dimer interactions. A serine residue (123) that hydrogen bonds to the corresponding residue in the neighbouring monomer was mutated to cysteine in an attempt to produce a stabilising disulphide bridge. Although the presence of a disulphide bridge was demonstrated, there was a slight reduction in stability of the mutant compared to the wild type enzyme, presumably owing to unfavourable dihedral angles.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:483469 |
| Date | January 1999 |
| Creators | Bunting, Karen Ann |
| Publisher | Birkbeck (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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