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Structural analysis of transcription factors involved in Mycobacterium tuberculosis mycolic acid biosynthesis

par Tanina, ABDALKARIM
Président du jury Fontaine, Véronique
Promoteur Wintjens, René
Co-Promoteur Wohlkönig, Alexandre
Publication Non publié, 2020-07-10

Thèse de doctorat

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Résumé :

Tuberculosis (TB) remains the leading cause of death due to a single infectious agent with more than 1.5 million people killed each year. In 2018, the World Health Organization (WHO) estimated that one third of the world’s population was infected with Mycobacterium tuberculosis (Mtb), the pathogen responsible for the disease.In 2000, EthR, a mycobacterial transcriptional repressor, was identified as a key modulator of ethionamide (ETH) bioactivation. ETH is one of the main second-line drugs used to treat drug-resistant strains and it is a prodrug that is activated in Mtb by the mono-oxygenase EthA and then inhibits InhA, an enzyme involved in the mycolic acid biosynthesis. In 2009, it was demonstrated that co-administration of ETH with the drug-like inhibitors of EthR was able to boost ETH activity by a factor three in a mouse-model of TB-infection, thus validating EthR protein as a target for a new therapeutic strategy. The first part of this thesis deals with the validation and deep characterization of the solved EthR-ligand structures based on all analysis of how each ligand bind to the EthR. In this section, based on the study of both co-crystal structures and the physicochemical properties of the ligands, we have rationalized the information currently available and understood the interaction of all EthR inhibitors in order to lead to more effective inhibitor design.More recently, another mycobaterial repressor, denoted EthR2, was identified as a putative target that appears to be functionally comparable to EthR (then the locus has been termed EthA2/EthR2, due to its similarity to the EthA/EthR locus). Furthermore, a spiroisoxazoline family of small-molecules, generically denoted as SMARt, has been identified as effective ligand of EthR2. However, according to the data present in the literature, this spiroisoxazoline family can also bind to the former EthR. In order to investigate this proposition, I have solved these small molecules in complex with EthR and compared their binding interactions to the EthR2 protein as well. The opportunity for the design small-molecules is capable of targeting both repressors, thereby opening the way to a dual-target approach.Finally, the third part of this thesis is devoted to the mycobacterial transcriptional factor MabR (Rv2242). Several studies identified this protein as a regulatory transcription factor of the fatty acid synthase II operon, which is mainly responsible for the mycolic acid biosynthesis in Mtb. I therefore purified to homogeneity and characterized the MabR protein as well as I determined the crystal structure of its C-terminal part. Finally, the functional role of MabR is largely discussed, and the way on how to interfere with its DNA binding ability is commented with respect to our results.