Design and signaling mechanism of light-regulated histidine kinases.

Signal transduction proteins are organized into sensor (input) domains that perceive a signal and, in response, regulate the biological activity of effector (output) domains. We reprogrammed the input signal specificity of a normally oxygen-sensitive, light-inert histidine kinase by replacing its chemosensor domain by a light-oxygen-voltage photosensor domain. Illumination of the resultant fusion kinase YF1 reduced net kinase activity by approximately 1000-fold in vitro. YF1 also controls gene expression in a light-dependent manner in vivo. Signals are transmitted from the light-oxygen-voltage sensor domain to the histidine kinase domain via a 40 degrees -60 degrees rotational movement within an alpha-helical coiled-coil linker; light is acting as a rotary switch. These signaling principles are broadly applicable to domains linked by alpha-helices and to chemo- and photosensors. Conserved sequence motifs guide the rational design of light-regulated variants of histidine kinases and other proteins.