Abstract
Phototropin (phot) is a blue-light receptor in plants. Phot has two FMN binding domains named LOV domain. In response to light absorption, a covalent adduct forms between a cysteine and FMN C(4a), which is called S390. According to the crystal structures of the LOV2 domain of Adiantum phytochrome3 (phy3), a chimeric phytochrome/phototropin, in the dark and S390 states, the side chain of Gln1029 switches hydrogen bond with FMN.
The structural changes were measured in the Q1029L mutant by low-temperature FTIR spectroscopy. It was implied that hydrogen-bond of FMN C(4)=O group is not formed in Q1029L. Upon formation of S390, hydrogen bond of C(4)=O becomes weaker in both WT and Q1029L. On the other hand, the protein structural changes of Q1029L were smaller than those of WT at room temperature.
These results suggest that the hydrogen-bonding interaction of Gln1029 with FMN plays an important role in the protein structural changes of phy3-LOV2.
