Temperature and urea induced conformational changes of the histidine kinases from Mycobacterium tuberculosis

A unique three protein two-component system is present in Mycobacterium tuberculosis comprising of two histidine kinases (Rv0600c/HK1 and Rv0601c/HK2) and a response regulator (Rv0602c/TcrA). The HK2 is a novel HPt-mono domain protein absent in other bacteria. We present here the temperature and urea induced denaturation study of HK1 and HK2 using circular dichroism and fluorescence spectroscopy. HK1 and HK2 are thermally quite stable. Thermal transition of HK1 is a two-state process and that of HK2 is a three-state process. Urea denaturation of HK1 and HK2 is a three-state and two-state process, respectively. The ΔG° of the two transitions during urea induced unfolding of HK1 is 4.76 ± 0.6 kcal/mol and −7.11 ± 0.8 kcal/mol. Unfolding of HK2 in presence of urea has ΔG° of 4.766 ± 0.5 kcal/mol. The intrinsic fluorescence study of HK2 unfolding implies flexibility of proline rich loop in the tryptophan bearing HAMP domain.