Abstract
Phototropin (phot), a blue light receptor in plant, is involved in phototropism, stomatal opening and chloroplast movement. Phot has two LOV (LOV1, LOV2) and a Ser/Thr kinase domains, in the N-terminal and the C-terminal regions, respectively. In the ground state, LOV2 acts as a main inhibitor of the kinase. Upon photoexcitation of LOV domain by blue light, a covalent bond is formed transiently between FMN and a conserved Cys. The adduct state returns to the ground state with time constants from seconds to minutes. The adduct formation induces conformational changes of LOV2 which cancels the inhibition. Then phot shows autophosphorelation.
In this study, we focused on Arg513 which interacts with the phosphate tail of FMN and prepared Arg513Lys mutant (R/K) of phot1 LOV2-kinase. R/K showed extremely shorter life time of the adduct state compared with the time of WT. Activation of the kinases were assayed under different light intensities. While the activity of WT was saturated at 10 μmol m-2 s-1, only a small activation was observed with R/K even at 200 μmol m-2 s-1. Molecular basis for the reduction of the kinase activation by light will be discussed.
