Partial proteolysis of rice phytochrome: comparison with oat phytochrome

Light modulation of histidine-kinase activity in bacterial phytochromes monitored by size exclusion chromatography, crosslinking, and limited proteolysis

Phytochromes are photoreceptors that have been found in plants, bacteria, and fungi. Most bacterial and fungal phytochromes are histidine kinases and, for several bacterial phytochromes, light regulation of kinase activity has been demonstrated. Typical histidine kinases are homodimeric proteins in which one subunit phosphorylates the substrate histidine residue of the other subunit; dimerization is an intrinsic property of the histidine kinase itself. Truncated phytochromes which lack the histidine kinase can also form dimers, but the interaction between subunits is modulated by light. This light-dependent dimerization can give a clue to the intramolecular signal transduction of phytochromes which modulates the histidine kinase activity. Size exclusion chromatography, limited proteolysis, and protein crosslinking can be used to study light-induced conformational changes and the interaction of subunits within the homodimer.