The response threshold of Salmonella PilZ domain proteins is determined by their binding affinities for c-di-GMP

• Published in: Molecular microbiology Vol. 86; no. 6; pp. 1424 - 1440
• Main Authors: Pultz, Ingrid Swanson, Christen, Matthias, Kulasekara, Hemantha Don, Kennard, Andrew, Kulasekara, Bridget, Miller, Samuel I.
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Publishing Ltd 01.12.2012; Blackwell
• Subjects: Bacteria; Bacterial Proteins - metabolism; Bacteriology; Binding sites; Biological and medical sciences; Cellulose; Cellulose - metabolism; Cyclic GMP - analogs & derivatives; Cyclic GMP - metabolism; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial; Inactivation; Locomotion; Microbiology; Miscellaneous; Molecules; Protein Binding; Proteins; Pseudomonas aeruginosa; Salmonella; Salmonella typhimurium - genetics; Salmonella typhimurium - metabolism; Salmonella typhimurium - physiology; Signal Transduction; Salmonella; Bacteria; Protein; Enterobacteriaceae
• ISSN: 0950-382X; 1365-2958; 1365-2958
• DOI: 10.1111/mmi.12066

Summary 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.