More Than Enzymes That Make or Break Cyclic Di-GMP-Local Signaling in the Interactome of GGDEF/EAL Domain Proteins of Escherichia coli

mBio. 2017 Oct 10;8(5):e01639-17. doi: 10.1128/mBio.01639-17.

Abstract

The bacterial second messenger bis-(3'-5')-cyclic diguanosine monophosphate (c-di-GMP) ubiquitously promotes bacterial biofilm formation. Intracellular pools of c-di-GMP seem to be dynamically negotiated by diguanylate cyclases (DGCs, with GGDEF domains) and specific phosphodiesterases (PDEs, with EAL or HD-GYP domains). Most bacterial species possess multiple DGCs and PDEs, often with surprisingly distinct and specific output functions. One explanation for such specificity is "local" c-di-GMP signaling, which is believed to involve direct interactions between specific DGC/PDE pairs and c-di-GMP-binding effector/target systems. Here we present a systematic analysis of direct protein interactions among all 29 GGDEF/EAL domain proteins of Escherichia coli Since the effects of interactions depend on coexpression and stoichiometries, cellular levels of all GGDEF/EAL domain proteins were also quantified and found to vary dynamically along the growth cycle. Instead of detecting specific pairs of interacting DGCs and PDEs, we discovered a tightly interconnected protein network of a specific subset or "supermodule" of DGCs and PDEs with a coregulated core of five hyperconnected hub proteins. These include the DGC/PDE proteins representing the c-di-GMP switch that turns on biofilm matrix production in E. coli Mutants lacking these core hub proteins show drastic biofilm-related phenotypes but no changes in cellular c-di-GMP levels. Overall, our results provide the basis for a novel model of local c-di-GMP signaling in which a single strongly expressed master PDE, PdeH, dynamically eradicates global effects of several DGCs by strongly draining the global c-di-GMP pool and thereby restricting these DGCs to serving as local c-di-GMP sources that activate specific colocalized effector/target systems.IMPORTANCE c-di-GMP signaling in bacteria is believed to occur via changes in cellular c-di-GMP levels controlled by antagonistic and potentially interacting pairs of diguanylate cyclases (DGCs) and c-di-GMP phosphodiesterases (PDEs). Our systematic analysis of protein-protein interaction patterns of all 29 GGDEF/EAL domain proteins of E. coli, together with our measurements of cellular c-di-GMP levels, challenges both aspects of this current concept. Knocking out distinct DGCs and PDEs has drastic effects on E. coli biofilm formation without changing the cellular c-di-GMP level. In addition, rather than generally coming in interacting DGC/PDE pairs, a subset of DGCs and PDEs operates as central interaction hubs in a larger "supermodule," with other DGCs and PDEs behaving as "lonely players" without contacts to other c-di-GMP-related enzymes. On the basis of these data, we propose a novel concept of "local" c-di-GMP signaling in bacteria with multiple enzymes that make or break the second messenger c-di-GMP.

Keywords: biofilms; c-di-GMP; cellulose; curli; diguanylate cyclase; second messenger.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / metabolism
  • Biofilms / growth & development
  • Cellulose / metabolism
  • Cyclic GMP / analogs & derivatives*
  • Cyclic GMP / genetics
  • Cyclic GMP / metabolism
  • Escherichia coli / chemistry*
  • Escherichia coli / enzymology
  • Escherichia coli / genetics*
  • Escherichia coli / metabolism
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / metabolism*
  • Gene Expression Regulation, Bacterial
  • Mutation
  • Phosphorus-Oxygen Lyases / metabolism
  • Protein Domains*
  • Protein Interaction Domains and Motifs
  • Signal Transduction

Substances

  • Bacterial Proteins
  • Escherichia coli Proteins
  • Crl protein, Bacteria
  • bis(3',5')-cyclic diguanylic acid
  • Cellulose
  • Phosphorus-Oxygen Lyases
  • diguanylate cyclase
  • Cyclic GMP