ATP-independent substrate recruitment to proteasomal degradation in mycobacteria

Life Sci Alliance. 2023 Aug 10;6(10):e202301923. doi: 10.26508/lsa.202301923. Print 2023 Oct.

Abstract

Mycobacteria and other actinobacteria possess proteasomal degradation pathways in addition to the common bacterial compartmentalizing protease systems. Proteasomal degradation plays a crucial role in the survival of these bacteria in adverse environments. The mycobacterial proteasome interacts with several ring-shaped activators, including the bacterial proteasome activator (Bpa), which enables energy-independent degradation of heat shock repressor HspR. However, the mechanism of substrate selection and processing by the Bpa-proteasome complex remains unclear. In this study, we present evidence that disorder in substrates is required but not sufficient for recruitment to Bpa-mediated proteasomal degradation. We demonstrate that Bpa binds to the folded N-terminal helix-turn-helix domain of HspR, whereas the unstructured C-terminal tail of the substrate acts as a sequence-specific threading handle to promote efficient proteasomal degradation. In addition, we establish that the heat shock chaperone DnaK, which interacts with and co-regulates HspR, stabilizes HspR against Bpa-mediated proteasomal degradation. By phenotypical characterization of Mycobacterium smegmatis parent and bpa deletion mutant strains, we show that Bpa-dependent proteasomal degradation supports the survival of the bacterium under stress conditions by degrading HspR that regulates vital chaperones.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Bacterial Proteins / metabolism
  • Heat-Shock Proteins* / genetics
  • Heat-Shock Proteins* / metabolism
  • Molecular Chaperones / metabolism
  • Mycobacterium tuberculosis* / chemistry
  • Mycobacterium tuberculosis* / metabolism
  • Proteasome Endopeptidase Complex / metabolism

Substances

  • Heat-Shock Proteins
  • Proteasome Endopeptidase Complex
  • Bacterial Proteins
  • Molecular Chaperones
  • Adenosine Triphosphate