A conserved regulatory switch controls phosphatase activity and specificity

Protein phosphatases must be regulated and specific for their substrates; how this control is achieved is critical for signaling by reversible phosphorylation. We recently reported the discovery of a regulatory switch that controls the activity of the PP2C family serine/threonine phosphatase SpoIIE from the bacterium Bacillus subtilis. This regulatory switch activates SpoIIE during spore development by forming the catalytically essential metal-binding site that is conserved across the PP2C family. We hypothesized that this switch is a conserved platform for regulating other PP2C phosphatases. An orthologous phosphatase from B. subtilis, RsbU, is activated under stress conditions and responds to different signals and acts on a different phosphoprotein substrate than SpoIIE. Using a combination of biochemical and genetic approaches, we find that broad features of the regulatory mechanism are conserved between SpoIIE and RsbU but that each phosphatase has adapted its response to be most appropriate for the distinct biological outputs it controls. In both cases, the switch accomplishes this by integrating substrate binding and recognition with regulatory inputs to control metal cofactor binding and catalysis. Thus, the switch is a conserved and mechanistically flexible regulatory platform that controls phosphatase activity and substrate specificity.