Photoreaction Dynamics of LOV1 and LOV2 of Phototropin from Chlamydomonas reinhardtii.

Phototropin is a blue light sensor protein found in higher plants and green algae. Photochemical reactions of a variety of differently truncated constructs of a phototropin from Chlamydomonas reinhardtii (Cr) (LOV1, LOV1-hinge, LOV2, LOV2-linker, and hinge-LOV2) are investigated. In the dark state, LOV1 is in dynamic equilibrium between the monomer and dimer, and the main photochemical reaction is dimerization of the monomer and dissociation of the dimer. On the other hand, LOV1-hinge exists as the monomer and the photochemical reaction is the dimerization reaction associated with the unfolding of the helix of the hinge domain. LOV2 in the dark state is monomeric. The conformation changes after the photoexcitation of LOV2 and LOV2-linker are minor, which differs notably from the reaction of LOV2-Jα and LOV2-linker from Arabidopsis thaliana (At). The linker region, including the Jα helix, is rather stable upon photoexcitation. The helix of the hinge domain of hinge-LOV2 is slightly unfolded in the dark state, and the major photoreaction is the dimerization event. The dark recovery rate of LOV2 was found to decrease significantly in the presence of the hinge domain. These photochemical properties of Cr phot are considerably different from those of At phot regarding conformational changes and their kinetics, although Cr phot has been reported to rescue the phot function in At. The differences and the diversity of phots are discussed.