Chapter 12: Mechanisms of Light Activation in Flavin-Binding Photoreceptors
Published:15 Sep 2006
Special Collection: 1968-2006 ebook collection
J. T. Kennis and M. T. Alexandre, in Flavins Photochemistry and Photobiology, ed. E. Silva, A. M. Edwards, D. Hader, and G. Jori, The Royal Society of Chemistry, 2006, vol. 6, ch. 12, pp. 287-320.
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Light, oxygen and voltage (LOV) and blue-light sensing using FAD (BLUF) domains constitute two classes of recently discovered photoreceptors that are found in plants, algae, fungi and bacteria. They are sensitive to blue light through a non-covalently bound flavin chromophore. LOV domains belong to the superfamily of PAS (PER/Arnt/Sim) sensor and regulatory domains, whereas BLUF domains make up a distinct family that shows no relationship to other sensor proteins. LOV domains undergo a photocycle involving light-driven covalent adduct formation between a conserved cysteine residue and the C(4a) atom of the flavin cofactor. In BLUF domains, light absorption initiates a photocycle that most likely involves a hydrogen-bond rearrangement between the flavin cofactor and the residues lining the flavin-binding pocket. In this chapter, an overview is given of the insights gained from biophysical studies into the functional properties of these novel photoreceptor proteins. The three-dimensional structures, steady-state and time-resolved spectroscopy and photocycles of LOV and BLUF domains are reviewed. Their photophysics and photochemistry are discussed in terms of proposed reaction mechanisms. Finally, the light-induced conformational changes that are required for the signaling function of these photoreceptor domains are considered.