Extracytoplasmic PAS-Like Domains Are Common in Signal Transduction Proteins

We present the crystal structure of the extracytoplasmic domain of the Bacillus subtilis PhoR sensor histidine kinase, part of a two-component system involved in adaptation to low environmental phosphate concentrations. In addition to the PhoR structure, we predict that the majority of the extracytoplasmic domains of B. subtilis sensor kinases will adopt a fold similar to the ubiquitous PAS domain.