Ligand-Mediated Biofilm Formation via Enhanced Physical Interaction between a Diguanylate Cyclase and Its Receptor.

David Giacalone,Holger Sondermann,T Jarrod Smith,Lori J Koziol,George A O'Toole,Alan J Collins,Joanna B Goldberg

doi:10.1128/mbio.01254-18

David Giacalone, Holger Sondermann + Show 5 more

Open Access

https://doi.org/10.1128/mbio.01254-18

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Journal: mBio	Publication Date: Jul 10, 2018
Citations: 42	License type: CC BY 4.0

Affiliation: Dartmouth College, Cornell University, New England College

Abstract

ABSTRACTThe bacterial intracellular second messenger, cyclic dimeric GMP (c-di-GMP), regulates biofilm formation for many bacteria. The binding of c-di-GMP by the inner membrane protein LapD controls biofilm formation, and the LapD receptor is central to a complex network of c-di-GMP-mediated biofilm formation. In this study, we examine how c-di-GMP signaling specificity by a diguanylate cyclase (DGC), GcbC, is achieved via interactions with the LapD receptor and by small ligand sensing via GcbC’s calcium channel chemotaxis (CACHE) domain. We provide evidence that biofilm formation is stimulated by the environmentally relevant organic acid citrate (and a related compound, isocitrate) in a GcbC-dependent manner through enhanced GcbC-LapD interaction, which results in increased LapA localization to the cell surface. Furthermore, GcbC shows little ability to synthesize c-di-GMP in isolation. However, when LapD is present, GcbC activity is significantly enhanced (~8-fold), indicating that engaging the LapD receptor stimulates the activity of this DGC; citrate-enhanced GcbC-LapD interaction further stimulates c-di-GMP synthesis. We propose that the I-site of GcbC serves two roles beyond allosteric control of this enzyme: promoting GcbC-LapD interaction and stabilizing the active conformation of GcbC in the GcbC-LapD complex. Finally, given that LapD can interact with a dozen different DGCs of Pseudomonas fluorescens, many of which have ligand-binding domains, the ligand-mediated enhanced signaling via LapD-GcbC interaction described here is likely a conserved mechanism of signaling in this network. Consistent with this idea, we identify a second example of ligand-mediated enhancement of DGC-LapD interaction that promotes biofilm formation.

Highlights

The bacterial intracellular second messenger, cyclic dimeric GMP (c-diGMP), regulates biofilm formation for many bacteria
A key open question relating to c-di-GMP signaling is how specificity of a particular output can be mediated in the context of up to dozens of enzymes or receptors making, breaking, and binding this dinucleotide second messenger
We show that an extracellular ligand can modulate the activity of a GcbC and does so via promoting interaction of the diguanylate cyclase (DGC) with its cognate receptor

Summary

Introduction

The bacterial intracellular second messenger, cyclic dimeric GMP (c-diGMP), regulates biofilm formation for many bacteria. We examine how c-di-GMP signaling specificity by a diguanylate cyclase (DGC), GcbC, is achieved via interactions with the LapD receptor and by small ligand sensing via GcbC’s calcium channel chemotaxis (CACHE) domain. Given that LapD can interact with a dozen different DGCs of Pseudomonas fluorescens, many of which have ligand-binding domains, the ligand-mediated enhanced signaling via LapD-GcbC interaction described here is likely a conserved mechanism of signaling in this network. Consistent with this idea, we identify a second example of ligand-mediated enhancement of DGCLapD interaction that promotes biofilm formation.

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