Kinetics of the LOV domain of ZEITLUPE determine its circadian function in Arabidopsis
Ashutosh Pudasaini,
Jae Sung Shim,
Young Hun Song,
Hua Shi,
Takatoshi Kiba,
David E Somers,
Takato Imaizumi,
Brian D Zoltowski
Affiliations
Ashutosh Pudasaini
Department of Chemistry, Southern Methodist University, Dallas, United States; Center for Drug Discovery, Design and Delivery, Southern Methodist University, Dallas, United States
Jae Sung Shim
Department of Biology, University of Washington, Seattle, United States
Young Hun Song
Department of Biology, University of Washington, Seattle, United States; Department of Life Sciences, Ajou University, Suwon, Korea
Hua Shi
Department of Molecular Genetics, Ohio State University, Columbus, United States
Takatoshi Kiba
RIKEN Center for Sustainable Resource Science, Yokohama, Japan
David E Somers
Department of Molecular Genetics, Ohio State University, Columbus, United States
Takato Imaizumi
Department of Biology, University of Washington, Seattle, United States
Department of Chemistry, Southern Methodist University, Dallas, United States; Center for Drug Discovery, Design and Delivery, Southern Methodist University, Dallas, United States
A LOV (Light, Oxygen, or Voltage) domain containing blue-light photoreceptor ZEITLUPE (ZTL) directs circadian timing by degrading clock proteins in plants. Functions hinge upon allosteric differences coupled to the ZTL photocycle; however, structural and kinetic information was unavailable. Herein, we tune the ZTL photocycle over two orders of magnitude. These variants reveal that ZTL complexes with targets independent of light, but dictates enhanced protein degradation in the dark. In vivo experiments definitively show photocycle kinetics dictate the rate of clock component degradation, thereby impacting circadian period. Structural studies demonstrate that photocycle dependent activation of ZTL depends on an unusual dark-state conformation of ZTL. Crystal structures of ZTL LOV domain confirm delineation of structural and kinetic mechanisms and identify an evolutionarily selected allosteric hinge differentiating modes of PAS/LOV signal transduction. The combined biochemical, genetic and structural studies provide new mechanisms indicating how PAS/LOV proteins integrate environmental variables in complex networks.
