A spectroelectrochemical investigation of the heme‐based sensor DevS from Mycobacterium tuberculosis: a redox versus oxygen sensor

Abstract

Tuberculosis is one of the oldest known infectious diseases, responsible for millions of deaths annually around the world. The ability of Mycobacterium tuberculosis (Mtb) to enter into a dormant state has been considered integral to the success of this bacterium as a human pathogen. One of the key systems involved in regulating the entrance into dormancy is the differentially expressed in virulent strain sensor protein (DevS) [(dormancy survival sensor protein (DosS)]. However, the physiological signal for DevS has remained unclear since it was first shown to be a heme‐based sensor with conflicting reports on whether it is a redox or an oxygen sensor. To address this question and provide a better understanding of the electronic properties of this protein, we present here, for the first time, a series of spectroelectrochemistry measurements of the full‐length holo DevS in anaerobic conditions as well as bound to CO, NO, imidazole (Imz), cyanide, and O2. An interesting feature of this protein is its ability to bind Imz even in the ferrous state, implying small‐molecule analogues could be designed as potential regulators. Nonetheless, a midpoint potential (Em) value of +10 mV [vs normal hydrogen electrode (NHE)] for DevS as measured under anaerobic conditions is much higher than the expected cytosolic potential for Mtb or even within stimulated macrophages (~ −270 mV vs NHE), indicating this sensor works in a reduced ferrous state. These data, along with the high oxygen affinity and very slow auto‐oxidation rate of DevS, provides evidence that it is not a redox sensor. Overall, this study validates the biological function of DevS as an oxygen sensor directly involved in the dormancy/latency of Mtb.

Heme-Based Gas Sensors in Nature and Their Chemical and Biotechnological Applications

“…These apparently conflicting conclusions were addressed by other studies as discussed elsewhere [36]. In summary, there is strong and compelling evidence supporting that DevS and DosT are indeed direct oxygen sensors, including DevS having a relatively high electrochemical potential (E m = −10 mV vs. NHE) [82]. But why nature would employ two oxygen sensors for that process?…”

Heme-Edge Residues Modulate Signal Transduction within a Bifunctional Homo-Dimeric Sensor Protein

“…This functional diversity is made possible by the tuning of heme properties through heme pocket amino acid side chains that directly coordinate the heme iron or provide residues within proximity to the heme macrocycle. Residues near the heme can interact with its vinyl or propionate substituents, possibly inducing out of plane distortions. , Variations in the heme pocket architecture, including resident water molecules, have yielded a diverse family of proteins with reduction potentials that span 1 V. − Within the larger hemoprotein family, heme sensor proteins are used throughout the kingdoms of life to sense gaseous ligands, such as nitric oxide (NO), carbon monoxide (CO), and oxygen (O 2 ), and typically contain a proximal histidine ligand and, for O 2 binding proteins, have a distal pocket with hydrogen bonding residues. − …”

Inhibiting DosRST As a New Approach to Tuberculosis Therapy

“…DosS is thought to function as a redox and oxygen sensor, based on biochemical studies of kinase activation, whereas, DosT is proposed to sense hypoxia [23,37]. However, a more recent study shows that DosS has a slow auto-oxidation rate and functions in the reduced ferrous state, supporting that DosS may primarily function as an oxygen sensor [42]. Both kinases sense ligands via the heme, where hypoxic conditions convert oxidized heme in DosS to the ferrous form, and O 2 -bound heme in DosT to the deoxy form, activating the kinases [23,38,40,41,43,44].…”