title: The response threshold of Salmonella PilZ domain proteins is determined by their binding affinities for c-di-GMP.
abstract: c-di-GMP is a bacterial second messenger that is enzymatically synthesized and degraded in response to environmental signals. Cellular processes are affected when c-di-GMP binds to receptors which include proteins that contain the PilZ domain. Although each c-di-GMP synthesis or degradation enzyme metabolizes the same molecule, many of these enzymes can be linked to specific downstream processes. Here we present evidence that c-di-GMP signalling specificity is achieved through differences in affinities of receptor macromolecules. We show that the PilZ domain proteins of Salmonella Typhimurium, YcgR and BcsA, demonstrate a 43-fold difference in their affinity for c-di-GMP. Modulation of the affinities of these proteins altered their activities in a predictable manner in vivo. Inactivation of yhjH, which encodes a predicted c-di-GMP degrading enzyme, increased the fraction of the cellular population that demonstrated c-di-GMP levels high enough to bind to the higher-affinity YcgR protein and inhibit motility, but not high enough to bind to the lower-affinity BcsA protein and stimulate cellulose production. Finally, PilZ domain proteins of Pseudomonas aeruginosa demonstrated a 145-fold difference in binding affinities, suggesting that regulation by binding affinity may be a conserved mechanism that allows organisms with many c-di-GMP binding macromolecules to rapidly integrate multiple environmental signals into one output.
authors.affiliation: Department of Microbiology, University of Washington, Seattle, WA 91895, USA.
authors.forename: Ingrid Swanson
authors.initials: IS
authors.lastname: Pultz
authors.forename: Matthias
authors.initials: M
authors.lastname: Christen
authors.forename: Hemantha Don
authors.initials: HD
authors.lastname: Kulasekara
authors.forename: Andrew
authors.initials: A
authors.lastname: Kennard
authors.forename: Bridget
authors.initials: B
authors.lastname: Kulasekara
authors.forename: Samuel I
authors.initials: SI
authors.lastname: Miller
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D002482:Cellulose / Q000378:metabolism; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008124:Locomotion; D011485:Protein Binding; D012486:Salmonella typhimurium / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction
chemical_list: D001426:Bacterial Proteins; C062025:bis(3',5')-cyclic diguanylic acid; D002482:Cellulose; D006152:Cyclic GMP