Reconstitution of a minimal ESX-5 type VII secretion system suggests a role for PPE proteins in the outer membrane transport of proteins

C. M. Bunduc, Y. Ding, C. Kuijl, T. C. Marlovits, W. Bitter, E. N. G. Houben

Research output: Contribution to journalArticleAcademicpeer-review

1 Citation (Scopus)

Abstract

Mycobacteria utilize type VII secretion systems (T7SSs) to secrete proteins across their highly hydrophobic and diderm cell envelope. Pathogenic mycobacteria have up to fivedifferentT7SSs, called ESX-1 to ESX-5, which are crucial for growth and virulence. Here, we use a functionally reconstituted ESX-5 system in the avirulent species Mycobacterium smegmatis that lacks ESX-5, to definethe role of each esx-5 gene in system functionality. By creating an array of gene deletions and assessing protein levels of components and membrane complex assembly, we observed that only the fivecomponents of the inner membrane complex are required for its assembly. However, in addition to these fivecore components, active secretion also depends on both the Esx and PE/PPE substrates. Tagging the PPE substrates followed by subcellular fractionation, surface labeling and membrane extraction showed that these proteins localize to the mycobacterial outer membrane. This indicates that they could play a role in secretion across this enigmatic outer barrier. These results provide the firstfull overview of the role of each esx-5 gene in T7SS functionality.

Original languageEnglish
Pages (from-to)e0040223
JournalmSphere
Volume8
Issue number5
Early online date25 Sept 2023
DOIs
Publication statusPublished - 24 Oct 2023

Keywords

  • ESX-5
  • minimal system
  • mycobacterium
  • secretion complex
  • type VII secretion

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