Light-activated bacterial LOV-domain histidine kinases

Bacteria rely on two-component signaling systems in their adaptive responses to environmental changes. Typically, the two-component system consists of a sensory histidine kinase that signals by transferring a phosphoryl group to a secondary response regulator that ultimately relays the signal to the cell. Some of these sensors use PAS (Per-Arnt-Sin) domains. A new member of the PAS super family is the LOV (light, oxygen, voltage) domain, a 10-kDa flavoprotein that functions as a light-sensory module in plant, algal, fungal, and bacterial blue-light receptors. Putative LOV domains have been identified in the genomes of many higher and lower eukaryotes, plants, eubacteria, archaebacteria, and particularly in genes coding for histidine kinases (LOV-histidine kinases, LOV-HKs) of plant and animal pathogenic bacteria, including Brucella. We describe here biochemical, photochemical, and biophysical methodology to purify these enzymes and to characterize their light-activation process.