COLLABORATIVE RESEARCH:Investigations of the Plant Photoreceptor Kinase Family of Phototropins

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0091384BriggsPlant photoreceptors mediate a broad spectrum of responses to light, ranging from the physiological through to the biochemical and molecular levels, and are present throughout plant development from seed germination through virtually all phases of vegetative growth to flowering and senescence. Currently well-known photoreceptors are phytochromes, cryptochromes, and phototropins. Phototropins represent a new and previously uncharacterized class of photoreceptors. These dual chromophoric photoreceptors, binding two molecules of FMN, are unlike any of the known classes of photoreceptors , and operate through an initial photochemistry that is unique and leads to autophosphorylation. The present project is focused on the chromoprotein phototropin (nph1) and the various nph1-like proteins described to date. These proteins are expressed in heterologous systems as the chromophore-binding domains and as the full length proteins. The expressed proteins both the native constructs and those with site-specific mutations are in the photoactive form. We plan to undertake a limited biochemical and detailed biophysical characterization of the various isolated chromophore-binding domains and of the full-length protein. The biochemical studies will emphasize the use of mutant constructs to probe the initial photochemistry. The latter will focus on studies probing the molecular mechanism by which light activates the photochemistry and its consequences at the protein level. These studies will involve time-resolved optical and vibrational spectroscopy. The chromophore-binding domains are closely related to domains (so-called PAS domains) in a diverse range of proteins from archaea through mammals, and should provide a new dimension to our understanding of the functions of these domains.