Expression and Purification of PhoR Sensor-Domain Histidine Kinase of Mycobacterium tuberculosis in Escherichia coli

Globally, tuberculosis (TB) remains a leading cause of death. The emergence of multidrug-resistant strains
(MDR-TB) and extensively drug-resistant strains (XDR-TB) has fuelled the discovery for novel drugs and drug
targets for its successful and better treatment. One of the potential candidates for drug target is PhoR sensory
protein histidine kinase, a part of the Two Component System (TCS) PhoP/PhoR in Mycobacterium tuberculosis
(Mtb). This protein system was known for its role on regulating hundred of Mtb virulence factors, from genes for
cell wall and lipid synthesis to genes for adaptation in human leukocyte and hypoxia response. Previous studies
have successfully characterized, isolated, and cloned theputative sensory domain of PhoR protein gene into
pRSET vector expression system. In this study, Escherichia coli was transformed with pRSET-SensPhoR and
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cultivated at 37 C under IPTG induction to express PhoR sensor-domain protein. Most of the proteins were
overexpressed in the form of inclusion bodies. Subsequent protein purification in Ni-NTA system under
refolding condition on urea gradient was performed to isolate PhoR sensor-domain protein in soluble form.
Arginine was supplemented in purified protein solution to prevent aggregation during long term storage. While
highly purified protein was acquired, small angle X-ray scattering (SAXS) analysis was conducted to obtain 3-
dimensional (3D) protein structures in solution.