Studies of light-induced structural changes in phytochrome using spin-label electron-electron double resonance

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Phytochromes are widespread photoreceptors with a bilin chromophore. These chromoproteins exist in two spectrally distinct forms, named Pr and Pfr. In this project we will study bacterial phytochrome Agp1 from Agrobacterium tumefaciens. Like many other bacterial phytochromes, Agp1 is a light-regulated histidine kinase. We plan to examine light-induced protein conformational changes of full-length Agp1 by using nitroxide-spin label electron paramagnetic resonance (EPR) techniques. The nitroxide label will be covalently attached to cysteine residues that are incorporated by site-directed mutagenesis. By measuring distances between spin labels using pulsed electron-electron double resonance (ELDOR), information on the arrangement of subunits within the dimer will be obtained. These measurements will provide insight into intramolecular signal transduction as well as structural information on a full-length phytochrome.