Oxygen affinities of DosT and DosS sensor kinases with implications for hypoxia adaptation in Mycobacterium tuberculosis

DosT and DosS are heme-based kinases involved in sensing and signaling O₂ tension in the microenvironment of Mycobacterium tuberculosis (Mtb). Under conditions of low O₂, they activate >50 dormancy-related genes and play a pivotal role in the induction of dormancy and associated drug resistance during tuberculosis infection. In this work, we reexamine the O₂ binding affinities of DosT and DosS to show that their equilibrium dissociation constants are 3.3±1.0 μM and 0.46±0.08 μM respectively, which are six to eight-fold stronger than what has been widely referred to in literature. Furthermore, stopped-flow kinetic studies reveal association and dissociation rate constants of 0.84 μM⁻¹ s⁻¹ and 2.8 s⁻¹, respectively for DosT, and 7.2 μM⁻¹ s⁻¹ and 3.3 s⁻¹, respectively for DosS. Remarkably, these tighter O₂ binding constants correlate with distinct stages of hypoxia-induced non-replicating persistence in the Wayne model of Mtb. This knowledge opens doors to deconvoluting the intricate interplay between hypoxia adaptation stages and the signal transduction capabilities of these important heme-based O₂ sensors.