The MprB Extracytoplasmic Domain Negatively Regulates Activation of the Mycobacterium tuberculosis MprAB Two-Component System

Abstract

Mycobacterium tuberculosis is an acid-fast pathogen of humans and the etiological agent of tuberculosis (TB). It is estimated that one-third of the world's population is latently (persistently) infected with M. tuberculosis. M. tuberculosis persistence is regulated, in part, by the MprAB two-component signal transduction system, which is activated by and mediates resistance to cell envelope stress. Here we identify MprAB as part of an evolutionarily conserved cell envelope stress response network and demonstrate that MprAB-mediated signal transduction is negatively regulated by the MprB extracytoplasmic domain (ECD). In particular, we report that deregulated production of the MprB sensor kinase, or of derivatives of this protein, negatively impacts M. tuberculosis growth. The observed growth attenuation is dependent on MprAB-mediated signal transduction and is exacerbated in strains of M. tuberculosis producing an MprB variant lacking its ECD. Interestingly, full-length MprB, and the ECD of MprB specifically, immunoprecipitates the Hsp70 chaperone DnaK in vivo, while overexpression of dnaK inhibits MprAB-mediated signal transduction in M. tuberculosis grown in the absence or presence of cell envelope stress. We propose that under nonstress conditions, or under conditions in which proteins present in the extracytoplasmic space are properly folded, signaling through the MprAB system is inhibited by the MprB ECD. Following exposure to cell envelope stress, proteins present in the extracytoplasmic space become unfolded or misfolded, leading to removal of the ECD-mediated negative regulation of MprB and subsequent activation of MprAB.

The Psp system of Mycobacterium tuberculosis integrates envelope stress‐sensing and envelope‐preserving functions

“…The evolutionary significance of this polymorphism remains to be ascertained. **Only M ycobacterium leprae was devoid of the entire ClgR ‐ P sp module, as previously reported ( B retl et al ., ), suggesting that loss of the P sp system is part of the genomic downsizing observed with this obligate intracellular pathogen ( C ole et al ., ). ***Only M ycobacterium avium among nontuberculous mycobacteria showed a truncated form of R v2742c (∼ 1/3 the length of M .…”

Rv2744c Is a PspA Ortholog That Regulates Lipid Droplet Homeostasis and Nonreplicating Persistence in Mycobacterium tuberculosis

“…MprAB, SigE, and PknB are three such regulatory factors that collectively mediate the resistance of M. tuberculosis to cell envelope stressors (reviewed in references 15 and 16). MprAB is a two-component signal transduction system that recognizes misfolded or unfolded proteins in the extracytoplasmic compartment (17). This system regulates a diverse set of Ͼ300 genes, including determinants encoding sigma factors, regulatory proteins, chaperones, proteases, and metabolic enzymes (18).…”

Chaperone-mediated stress-sensing in Mycobacterium tuberculosis enables fast activation and sustained response

“…To resolve the inconsistency, we propose a more complex model for MprB activation. This model introduces DnaK, a chaperone that deactivates MprB in unstressed conditions [3]. Unfolded membrane proteins accumulated following SDS exposure compete with MprB for DnaK, eventually activating MprAB TCS.…”