How TB's DosR protein switches bacteria into dormancy

Tuberculosis remains a major global threat because the bacterium Mycobacterium tuberculosis (Mtb) can enter a dormant state that lets it survive for years in the human body. This latent infection is hard to treat and underlies the persistence and recrudescence of disease. Scientists have long recognized DosR as a central regulator of that dormant state: it controls a broad set of genes that let Mtb adapt to low-oxygen, stressful environments encountered inside human cells. But until now the precise molecular steps by which DosR turns on those genes were not well understood. Jing Shi and colleagues set out to fill that gap. They studied how DosR interacts directly with the cellular machinery that reads DNA to make RNA, looking specifically at conditions that mimic the low-oxygen, or hypoxic, promoters relevant for dormancy. By assembling the protein complexes that form when DosR activates transcription, and determining their structure, the team aimed to reveal the physical rearrangements and contacts that allow DosR to switch genes on and help Mtb persist.

The core achievement reported by Jing Shi is the determination of a cryo-EM structure of an intact DosR-dependent transcriptional activation complex (DosR-TAC). The complex includes Mtb RNA polymerase (RNAP), DosR, and a hypoxic promoter DNA fragment. In this assembly two DosR monomers form a symmetric dimer, engaging through their N-terminal receiver domains (DosR_RECs) and the α10 helices of their C-terminal DNA-binding domains (DosR_DBDs). The structure reveals that the DosR dimer adopts a different configuration from its previously observed inhibitory form: conformational changes occur in the original linker region, which isomerizes DosR_REC into a canonical (βα)5 fold. That extended linker positions the DosR_DBDs and DosR I _REC to contact the promoter DNA and simultaneously makes contacts with conserved regions of RNAP, including σ A R4, αCTD, and αNTD. Complementary functional tests — RT-qPCR and growth curve assays performed on wild-type and DosR mutant strains — showed the physiological importance of this divergent linker and support the structural observations. Taken together, these results underpin an 'allosteric activation-recruitment' model for DosR action.

These findings illuminate a molecular choreography that explains how DosR both changes shape and recruits the transcription machinery to turn on genes needed for dormancy survival. By revealing the exact interfaces and the role of the linker that connects DosR domains, the work provides specific structural targets that could be explored in future efforts to prevent or disrupt dormancy. Interrupting the ability of DosR to adopt the active configuration, to contact promoter DNA, or to interact with RNAP domains such as σ A R4, αCTD, and αNTD could, in principle, blunt Mtb’s capacity to persist in a latent state. Beyond drug discovery, the structure offers a clear framework for interpreting genetic mutations that affect dormancy and for designing experiments to test small molecules or biological agents that interfere with DosR-TAC formation. By combining cryo-EM with RT-qPCR and growth curve assays, Jing Shi’s study moves the field from models and hypotheses to a concrete molecular picture of how dormancy is established and maintained in Mtb.