Power Density Titration of Reversible Photoisomerization of a Fluorescent Protein Chromophore in the Presence of Thermally Driven Barrier Crossing Shown by Quantitative Millisecond Serial Synchrotron X-ray Crystallography.

We present millisecond quantitative serial X-ray crystallography at 1.7 Å resolution demonstrating precise optical control of reversible population transfer from Trans-Cis and Cis-Trans photoisomerization of a reversibly switchable fluorescent protein, rsKiiro. Quantitative results from the analysis of electron density differences, extrapolated structure factors, and occupancy refinements are shown to correspond to optical measurements of photoinduced population transfer and have sensitivity to a few percent in concentration differences.

Time-resolved crystallography captures light-driven DNA repair.

Photolyase is an enzyme that uses light to catalyze DNA repair. To capture the reaction intermediates involved in the enzyme's catalytic cycle, we conducted a time-resolved crystallography experiment. We found that photolyase traps the excited state of the active cofactor, flavin adenine dinucleotide (FAD), in a highly bent geometry.

Optical control of ultrafast structural dynamics in a fluorescent protein.

The photoisomerization reaction of a fluorescent protein chromophore occurs on the ultrafast timescale. The structural dynamics that result from femtosecond optical excitation have contributions from vibrational and electronic processes and from reaction dynamics that involve the crossing through a conical intersection. The creation and progression of the ultrafast structural dynamics strongly depends on optical and molecular parameters.

Serial Femtosecond Crystallography Reveals that Photoactivation in a Fluorescent Protein Proceeds via the Hula Twist Mechanism.

Chromophore photoisomerization is a fundamental process in chemistry and in the activation of many photosensitive proteins. A major task is understanding the effect of the protein environment on the efficiency and direction of this reaction compared to what is observed in the gas and solution phases. In this study, we set out to visualize the hula twist (HT) mechanism in a fluorescent protein, which is hypothesized to be the preferred mechanism in a spatially constrained binding pocket.

Light activation of Orange Carotenoid Protein reveals bicycle-pedal single-bond isomerization.

Orange Carotenoid protein (OCP) is the only known photoreceptor which uses carotenoid for its activation. It is found exclusively in cyanobacteria, where it functions to control light-harvesting of the photosynthetic machinery. However, the photochemical reactions and structural dynamics of this unique photosensing process are not yet resolved.