Masahide Terazima

Despite a five-residue difference, eGFP and eYFP exhibit different dimerization affinities and different transition dipole moment angles within the homodimer.

The Orange carotenoid protein (OCP) is a blue-green light sensor that regulates nonphotochemical quenching in cyanobacteria through reversible transitions between its dark-adapted (OCP^O) and light-adapted (OCP^R) states. Despite extensive studies, the detailed reaction scheme remains unclear. In this study, we examined the photoinduced reaction dynamics of OCP using size-exclusion chromatography (SEC), small-angle X-ray scattering (SAXS), and transient grating (TG) spectroscopy. We found that OCP^O and OCP^R exist in monomer-dimer equilibria, but the OCP^R dimer forms a more stable and elongated shape than the OCP^O dimer. The TG measurements revealed that upon photoexcitation, OCP^O monomers undergo two structural transitions before associating into OCP^R dimers. In contrast, the OCP^O dimer dissociates prior to the structural rearrangement, highlighting a fundamental difference in their reaction pathways. Moreover, the dimerization was found to moderately reduce the photoreactivity of OCP^O compared to the monomer. We also found that apo-OCP readily forms a heterodimer with OCP^R, potentially altering reaction pathways and changing intrinsic kinetic behavior.

Reaction and interaction dynamics of azobenzene-tethered DNA with T7 RNA polymerase were studied after photoisomerization of azobenzene from the cis - to trans -forms using the transient grating and time-resolved fluorescence polarization techniques.

To analyze hydration effects on macromolecular diffusion, the friction coefficients of macromolecules were examined using molecular dynamics simulations with an all-atom model. In the present study, a method was introduced to decompose the molecular friction coefficient into the contributions for each site on the macromolecule. The method was applied to several fullerenols in ambient water. The friction coefficients for the hydrophilic part, such as the OH group, were larger than those for the hydrophobic part, such as the C. The hydration effect did not depend only on the kind of functional group but also on the surface roughness. This approach would be useful in explaining the experimentally observed large changes in diffusion coefficients of proteins that were accompanied by conformation changes.

A sensor of blue‐light using flavin adenine dinucleotide (BLUF) is a typical blue light photoreceptor domain that is found in many photosensor proteins in bacteria and some eukaryotic algae. SyPixD in Synechocystis is one of the well‐studied BLUF proteins. In the dark state, it forms a decamer and, upon photoexcitation, a dissociation reaction takes place to yield dimers. Such change in the intermolecular interactions of the protomers is important for the biological function. The effect of the N‐ and C‐terminal sequences on the stability of SyPixD oligomeric states and photoreactions of SyPixD were studied to understand how the oligomeric form is maintained with weak interaction. It was found that a few residues that frequently persist at the N‐terminus after removing a tag for purification are sensitive to the stability of the decamer structure. Even two or three residues at the N‐terminus considerably reduces decamer stability, whereas four or more residues completely prevent decamer formation. Unexpectedly, truncating C‐terminal sequences, which locate far from any protomer interface and of which structure is undetermined in crystal structure, also destabilizes the decamer structure. This destabilization is also apparent from the dissociation reaction dynamics detected by the transient grating and transient absorption measurements. The dissociation reaction is faster and the yield increases when the C‐terminus does not contain seven amino acid residues. Photoexcitation induces a conformational change in the C‐terminus of the decamer but not the dimer.

Reaction scheme of heliorhodopsin. Diffusion measurement reveals a conformational change in the characteristic helix on the cytoplasmic side (ICL1 helix).

A time-resolved biosensor method using optically detected diffusion is used to reveal a light signal transduction process of a photosensor protein. This method expands targets of biosensor for transient species.

Photoinduced protein-protein interaction of a BLUF domain from Bldp1 (eBLUF) is investigated by the transient grating techniques. The result demonstrsates that this protein and some site-directed mutants are suitable for optical control of bioactivity.