Abstract
BackgroundProper phosphate signaling is essential for robust growth of Escherichia coli and many other bacteria. The phosphate signal is mediated by a classic two component signal system composed of PhoR and PhoB. The PhoR histidine kinase is responsible for phosphorylating/dephosphorylating the response regulator, PhoB, which controls the expression of genes that aid growth in low phosphate conditions. The mechanism by which PhoR receives a signal of environmental phosphate levels has remained elusive. A transporter complex composed of the PstS, PstC, PstA, and PstB proteins as well as a negative regulator, PhoU, have been implicated in signaling environmental phosphate to PhoR.ResultsThis work confirms that PhoU and the PstSCAB complex are necessary for proper signaling of high environmental phosphate. Also, we identify residues important in PhoU/PhoR interaction with genetic analysis. Using protein modeling and docking methods, we show an interaction model that points to a potential mechanism for PhoU mediated signaling to PhoR to modify its activity. This model is tested with direct coupling analysis.ConclusionsThese bioinformatics tools, in combination with genetic and biochemical analysis, help to identify and test a model for phosphate signaling and may be applicable to several other systems.
Highlights
Proper phosphate signaling is essential for robust growth of Escherichia coli and many other bacteria
Plasmids, and reconstructing of signaling system Plasmids that were used include pKG116 [9], p116U2 [7], p116A147E, p116U2 A147K, p116U2 R148A, p116U2 R148E, p116U2 D150A
To determine whether PhoU could act independently of the phosphate specific ABC transporter complex (PstSCAB) transporter, we expressed these two genetic entities from separate plasmids in E. coli strain BW26337, which contains a deletion of the pstSCABphoU operon and tested strains for control of the Pho regulon
Summary
Proper phosphate signaling is essential for robust growth of Escherichia coli and many other bacteria. Bacteria have several mechanisms to scavenge phosphate that are only expressed when the level of available environmental phosphate is limited: including a phosphate specific ABC transporter complex (PstSCAB) and a periplasmic phosphate scavenging enzyme (alkaline phosphatase (AP); the product of the phoA gene) [1] Expression control of these genes is essential for optimal growth and has been implicated in the regulation of pathogenesis in several organisms [2,3]. In Escherichia coli, a classic two-component signal transduction system, composed of the PhoR histidine kinase and the PhoB response regulator, is responsible for expression control of a group of genes called the Pho regulon. The mechanism of this signal has not been fully elucidated
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