Single GAF Domain Phytochrome Exhibits a pH-Dependent Shunt on the Millisecond Timescale.

The light-sensing activity of phytochromes is based on the reversible light-induced switching between two isomerization states of the bilin chromophore. These photo-transformations may not necessarily be only unidirectional, but could potentially branch back to the initial ground state in a thermally driven process termed shunt. Such shunts have been rarely reported, and thus our understanding of this process and its governing factors are limited.

Photoswitch dissociation from a G protein-coupled receptor resolved by time-resolved serial crystallography.

G protein-coupled receptors (GPCRs) are the largest family of cell surface receptors in humans. The binding and dissociation of ligands tunes the inherent conformational flexibility of these important drug targets towards distinct functional states. Here we show how to trigger and resolve protein-ligand interaction dynamics within the human adenosine A receptor.

Kinetic Basis for the Design of Azobenzene-Based Photoswitchable A Adenosine Receptor Ligands.

Photoisomerization of ligands is a key process in the field of photopharmacology. Thus, the kinetics and efficiency of this initial photoreaction are of great importance but can be influenced by the molecular environment of the binding pocket and the resulting confinement of the reaction pathway. In this study, we investigated the photoisomerization of an azobenzene derivative of the anti-Parkinson's drug istradefylline.

A Detailed View on the (Re)isomerization Dynamics in Microbial Rhodopsins Using Complementary Near-UV and IR Readouts.

Isomerization is a key process in many (bio)chemical systems. In microbial rhodopsins, the photoinduced isomerization of the all-trans retinal to the 13-cis isomer initiates a cascade of structural changes of the protein. The interplay between these changes and the thermal relaxation of the isomerized retinal is one of the crucial determinants for rhodopsin functionality.

Rotameric Heterogeneity of Conserved Tryptophan Is Responsible for Reduced Photochemical Quantum Yield in Cyanobacteriochrome Slr1393g3.

The red/green cyanobacteriochrome (CBCR) slr1393g3 exhibits a quantum yield of only 8 % for its forward photoconversion, significantly lower than other species from the same CBCR subfamily. The cause for this reduced photoconversion is not yet clear, although in the related NpR6012g4 dark-state structural heterogeneity of a paramount Trp residue has been proposed to cause the formation of nonproductive subpopulation. However, there is no such information on the equivalent residue in slr1393g3, W496.