Structural Characterisation of MenJ, a Novel Oxidoreductase Involved in Mycobacterium tuberculosis virulence

Abstract

According to the World Health Organisation, tuberculosis (TB) has recently become the leading cause of death due to infectious disease, surpassing HIV. Challenges to the treatment of TB include drug resistant strains of the causative pathogen, Mycobacterium tuberculosis (Mtb), and the latency of the bacterium that allows it to persist in a non-replicative, drug-insensitive state. To address these challenges, new therapeutics must be designed that target novel mechanisms essential for Mtb's survival. One such mechanism is the partial saturation of menaquinone, the lipoquinone that functions to ferry electrons across the electron transport chain during oxidative phosphorylation. The enzyme catalysing this reaction, MenJ, is non-essential for in vitro growth but is conditionally essential for Mtb's survival within host macrophages. Thus, inhibition of MenJ would potentially prevent Mtb from surviving within macrophages. MenJ is a FAD-containing protein, homologous to bacterial geranylgeranyl reductases. Despite Mtb utilising menaquinone as the sole lipoquinone in vivo, MenJ has been shown to recognise both menaquinone and ubiquinone in vitro and localise to the cell membrane. Understanding substrate recognition by regiospecificity and the mechanism of membrane adherence would be enabled by a high-resolution crystal structure of MenJ. The primary aim of this project was to produce protein crystals of MenJ from Mtb or Mycobacterium smegmatis suitable for X-ray diffraction analysis, which would be the first step in a target-based drug discovery approach to the design of MenJ inhibitors.