title: Allosteric activation of exopolysaccharide synthesis through cyclic di-GMP-stimulated protein-protein interaction.
abstract: In many bacterial pathogens, the second messenger c-di-GMP stimulates the production of an exopolysaccharide (EPS) matrix to shield bacteria from assaults of the immune system. How c-di-GMP induces EPS biogenesis is largely unknown. Here, we show that c-di-GMP allosterically activates the synthesis of poly-β-1,6-N-acetylglucosamine (poly-GlcNAc), a major extracellular matrix component of Escherichia coli biofilms. C-di-GMP binds directly to both PgaC and PgaD, the two inner membrane components of the poly-GlcNAc synthesis machinery to stimulate their glycosyltransferase activity. We demonstrate that the PgaCD machinery is a novel type c-di-GMP receptor, where ligand binding to two proteins stabilizes their interaction and promotes enzyme activity. This is the first example of a c-di-GMP-mediated process that relies on protein-protein interaction. At low c-di-GMP concentrations, PgaD fails to interact with PgaC and is rapidly degraded. Thus, when cells experience a c-di-GMP trough, PgaD turnover facilitates the irreversible inactivation of the Pga machinery, thereby temporarily uncoupling it from c-di-GMP signalling. These data uncover a mechanism of c-di-GMP-mediated EPS control and provide a frame for c-di-GMP signalling specificity in pathogenic bacteria.
authors.affiliation: Biozentrum, University of Basel, 4056 Basel, Switzerland.
authors.forename: Samuel
authors.initials: S
authors.lastname: Steiner
authors.forename: Christian
authors.initials: C
authors.lastname: Lori
authors.forename: Alex
authors.initials: A
authors.lastname: Boehm
authors.forename: Urs
authors.initials: U
authors.lastname: Jenal
mesh_terms: D000494:Allosteric Regulation / Q000502:physiology*; D018441:Biofilms / Q000254:growth & development*; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000378:metabolism; D004926:Escherichia coli / Q000254:growth & development* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000096:biosynthesis*; D016695:Glycosyltransferases / Q000378:metabolism; D015151:Immunoblotting; D047468:Immunoprecipitation; D008958:Models, Molecular; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*; D015290:Second Messenger Systems / Q000502:physiology*; D047071:beta-Glucans
chemical_list: D029968:Escherichia coli Proteins; D016326:Extracellular Matrix Proteins; D011135:Polysaccharides, Bacterial; D047071:beta-Glucans; C505465:poly-N-acetyl-1-6-glucosamine; C062025:bis(3',5')-cyclic diguanylic acid; D016695:Glycosyltransferases; D006152:Cyclic GMP