Insights into the structure and assembly of a bacterial cellulose secretion system

Nat Commun. 2017 Dec 12;8(1):2065. doi: 10.1038/s41467-017-01523-2.


Secreted exopolysaccharides present important determinants for bacterial biofilm formation, survival, and virulence. Cellulose secretion typically requires the concerted action of a c-di-GMP-responsive inner membrane synthase (BcsA), an accessory membrane-anchored protein (BcsB), and several additional Bcs components. Although the BcsAB catalytic duo has been studied in great detail, its interplay with co-expressed subunits remains enigmatic. Here we show that E. coli Bcs proteins partake in a complex protein interaction network. Electron microscopy reveals a stable, megadalton-sized macromolecular assembly, which encompasses most of the inner membrane and cytosolic Bcs components and features a previously unobserved asymmetric architecture. Heterologous reconstitution and mutational analyses point toward a structure-function model, where accessory proteins regulate secretion by affecting both the assembly and stability of the system. Altogether, these results lay the foundation for more comprehensive models of synthase-dependent exopolysaccharide secretion in biofilms and add a sophisticated secretory nanomachine to the diverse bacterial arsenal for virulence and adaptation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological / physiology
  • Bacterial Secretion Systems / chemistry
  • Bacterial Secretion Systems / metabolism*
  • Biofilms
  • Cellulose / metabolism*
  • Cyclic GMP / metabolism
  • DNA Mutational Analysis
  • Escherichia coli / physiology*
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / isolation & purification
  • Escherichia coli Proteins / metabolism*
  • Escherichia coli Proteins / ultrastructure
  • Membrane Proteins / chemistry
  • Membrane Proteins / isolation & purification
  • Membrane Proteins / metabolism*
  • Membrane Proteins / ultrastructure
  • Microscopy, Electron
  • Models, Biological
  • Protein Binding
  • Protein Domains / physiology
  • Protein Interaction Maps / physiology
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / isolation & purification
  • Recombinant Proteins / metabolism
  • Recombinant Proteins / ultrastructure
  • Software
  • Structure-Activity Relationship


  • Bacterial Secretion Systems
  • Escherichia coli Proteins
  • Membrane Proteins
  • Recombinant Proteins
  • Cellulose
  • Cyclic GMP