Two Faces of CwlM, an Essential PknB Substrate, in Mycobacterium tuberculosis

Cell Rep. 2018 Oct 2;25(1):57-67.e5. doi: 10.1016/j.celrep.2018.09.004.


Tuberculosis claims >1 million lives annually, and its causative agent Mycobacterium tuberculosis is a highly successful pathogen. Protein kinase B (PknB) is reported to be critical for mycobacterial growth. Here, we demonstrate that PknB-depleted M. tuberculosis can replicate normally and can synthesize peptidoglycan in an osmoprotective medium. Comparative phosphoproteomics of PknB-producing and PknB-depleted mycobacteria identify CwlM, an essential regulator of peptidoglycan synthesis, as a major PknB substrate. Our complementation studies of a cwlM mutant of M. tuberculosis support CwlM phosphorylation as a likely molecular basis for PknB being essential for mycobacterial growth. We demonstrate that growing mycobacteria produce two forms of CwlM: a non-phosphorylated membrane-associated form and a PknB-phosphorylated cytoplasmic form. Furthermore, we show that the partner proteins for the phosphorylated and non-phosphorylated forms of CwlM are FhaA, a fork head-associated domain protein, and MurJ, a proposed lipid II flippase, respectively. From our results, we propose a model in which CwlM potentially regulates both the biosynthesis of peptidoglycan precursors and their transport across the cytoplasmic membrane.

Keywords: CwlM; MurJ; Mycobacterium tuberculosis; cellular localization; peptidoglycan; phosphoproteomics; protein kinase B; serine/threonine protein kinase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cell Wall / enzymology
  • Mycobacterium tuberculosis / cytology
  • Mycobacterium tuberculosis / enzymology*
  • Mycobacterium tuberculosis / growth & development
  • N-Acetylmuramoyl-L-alanine Amidase / metabolism*
  • Phosphorylation
  • Proto-Oncogene Proteins c-akt / deficiency
  • Proto-Oncogene Proteins c-akt / metabolism*


  • Proto-Oncogene Proteins c-akt
  • N-Acetylmuramoyl-L-alanine Amidase