Photoexcited structure of a plant photoreceptor domain reveals a light-driven molecular switch.
The phototropins are flavoprotein kinases that control phototropic bending, light-induced chloroplast movement, and stomatal opening in plants. Two flavin mononucleotide binding light, oxygen, or voltage (LOV) domains are the sites for initial photochemistry in these blue light photoreceptors. We have determined the steady state, photoexcited crystal structure of a flavin-bound LOV domain. The structure reveals a unique photochemical switch in the flavin binding pocket in which the absorption of light drives the formation of a reversible covalent bond between a highly conserved Cys residue and the flavin cofactor. This provides a molecular picture of a cysteinyl-flavin covalent adduct, the presumed signaling species that leads to phototropin kinase activation and subsequent signal transduction. We identify closely related LOV domains in two eubacterial proteins that suggests the light-induced conformational change evident in this structure is an ancient biomolecular response to light, arising before the appearance of plants.
Crosson
Sean
S
Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637, USA.
Moffat
Keith
K
D000595:Amino Acid Sequence; D001692:Biological Transport / Q000528:radiation effects; D002736:Chloroplasts / Q000502:physiology / Q000528:radiation effects; D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; D005486:Flavin Mononucleotide / Q000235:genetics* / Q000378:metabolism; D005420:Flavoproteins / Q000235:genetics* / Q000378:metabolism; D008027:Light; D008564:Membrane Potentials / Q000502:physiology / Q000528:radiation effects; D008969:Molecular Sequence Data; D010100:Oxygen / Q000378:metabolism; D017956:Photoreceptor Cells, Invertebrate; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics* / Q000528:radiation effects; D018524:Phototropism / Q000528:radiation effects; D018514:Plant Structures / Q000502:physiology / Q000528:radiation effects; D043562:Receptors, G-Protein-Coupled; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000528:radiation effects
D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins; D045322:Photosynthetic Reaction Center Complex Proteins; D043562:Receptors, G-Protein-Coupled; C119828:cry protein, Drosophila; D005486:Flavin Mononucleotide; D010100:Oxygen