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Title: Characterisation of the essential transcription factor, WhiB1, from Mycobacterium tuberculosis
Author: Smith, L.
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2012
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Mycobacterium tuberculosis is a major human pathogen, infecting approximately one third of the world's population. The majority of infected individuals are asymptomatic, and in these cases M. tuberculosis is present in a non-replicating persistent state. Mycobacterium tuberculosis is capable of emerging from this persistent state and causing active disease. Extensive gene regulation facilitates the entry into and emergence from the persistent state, and understanding this reprogramming of genes may help provide novel methods of treatment. The cAMP receptor protein Rv3676 is a global gene regulator in M. tuberculosis that is required for virulence, regulating ~100 genes including whiB1. The whiB1 gene encodes a member of the Wbl family of proteins, which are iron-sulphur cluster-containing transcription factors associated with a role in developmental processes in the actinomycetes. WhiB1, one of seven Wbl proteins encoded by M. tuberculosis, was the focus of this study. The whiB1 gene was identified as being essential for M. tuberculosis survival. The WhiB1 protein incorporated a [4Fe-4S] cluster, ligated by four essential cysteine residues, which was stable in the presence of oxygen but reacted rapidly with nitric oxide in a multiphasic reaction forming an unusual octa-nitrosylated cluster. The reduced and oxidised apo-WhiB1 bound both the whiB1 and groEL2 promoter regions, but the [4Fe-4S] containing form of WhiB1 (holo-WhiB1) was unable to bind DNA. Treatment of holo-WhiB1 with nitric oxide led to restoration of DNA-binding. The DNA-binding capabilities of WhiB1 were found to be, in part, due to specific amino acid residues in the helix-turn-helix region of the protein. Transcription of whiB1 is negatively-regulated by apo-WhiB1 in both the presence and absence of Rv3676, which has been identified as activating whiB1 expression. Thus whiB1 expression is regulated by two important infection signals viz. nitric oxide and cAMP, suggesting a role for WhiB1 in tuberculosis pathogenesis.
Supervisor: Green, J. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available