| Tuberculosis (TB) is a devastating infectious disease caused by the bacterium Mycobacterium tuberculosis. The ability to persist in host tissues for a long period of time makes M. tuberculosis an unusually successful pathogen, causing latent TB infection in one third of the world's population. The ability to uptake scarcely available iron during infection using the siderophore-mediated iron uptake system makes M. tuberculosis highly virulent and capable to replicate inside the host. The iron-dependent regulator (IdeR) controls the iron-uptake system and is essential for survival of M. tuberculosis under low iron conditions. When facing low oxygen tension or nitric oxide exposure, M. tuberculosis uses the two-component regulatory system DosS-DosR to switch into a dormant state, which may lead to latent TB infection. The research described in this dissertation focuses on structures and functions of two important M. tuberculosis transcription regulators, IdeR and DosR, and their complexes with DNA, which provide platforms for future rational anti-TB drug design.; Structures of IdeR-DNA complex reveal IdeR binding to DNA duplex as a "double-dimer" complex with two dimers on opposite sides of the DNA. The SH3-like third domain adopts a "wedge" position to interact with the other two domains, and provides two ligands for metal site 1. Ser37 and Pro39 make specific interactions with conserved thymine bases.; Full-length DosR exhibits an unusual (betaalpha)4 topology of the receiver domain and an extensive interaction with the receiver domain of helix alpha10 in a novel position in the DNA binding domain. Our panel of structures suggests a "three helix displacement" mechanism with helices alpha4, alpha5, and alpha10 adopting canonical positions when DosR is activated by phosphorylation of Asp54. Dimerization of the DNA-binding domain using the alpha10 helix interface enables DosR to bind cognate DNA with its alpha9 helix. |
