Domestication of a housekeeping transglycosylase for assembly of a Type VI secretion system

EMBO Rep. 2017 Jan;18(1):138-149. doi: 10.15252/embr.201643206. Epub 2016 Dec 5.


The type VI secretion system (T6SS) is an anti-bacterial weapon comprising a contractile tail anchored to the cell envelope by a membrane complex. The TssJ, TssL, and TssM proteins assemble a 1.7-MDa channel complex that spans the cell envelope, including the peptidoglycan layer. The electron microscopy structure of the TssJLM complex revealed that it has a diameter of ~18 nm in the periplasm, which is larger than the size of peptidoglycan pores (~2 nm), hence questioning how the T6SS membrane complex crosses the peptidoglycan layer. Here, we report that the MltE housekeeping lytic transglycosylase (LTG) is required for T6SS assembly in enteroaggregative Escherichia coli Protein-protein interaction studies further demonstrated that MltE is recruited to the periplasmic domain of TssM. In addition, we show that TssM significantly stimulates MltE activity in vitro and that MltE is required for the late stages of T6SS membrane complex assembly. Collectively, our data provide the first example of domestication and activation of a LTG encoded within the core genome for the assembly of a secretion system.

Keywords: multiprotein assembly; peptidoglycan; protein complex; protein transport; secretion system.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism
  • Genes, Essential*
  • Glycosyltransferases / chemistry
  • Glycosyltransferases / genetics*
  • Glycosyltransferases / metabolism*
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Models, Biological
  • Protein Binding
  • Protein Interaction Domains and Motifs
  • Protein Multimerization
  • Type VI Secretion Systems*


  • Escherichia coli Proteins
  • Membrane Proteins
  • TssM protein, E coli
  • Type VI Secretion Systems
  • Glycosyltransferases
  • MltE protein, E coli