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Determination of the architecture of an invertebrate photoreceptor protein, squid rhodopsin, is a notable event. It illuminates the mechanism of invertebrate vision and a ubiquitous intracellular signalling system.

Opsins are responsible for light perception across the animal kingdom. Here the authors show cryo-EM structures of an activated bistable opsin, shedding light on the activation mechanism of this class of bidirectional photoswitches.

One picosecond after photoactivation, isomerized retinal pulls away from half of its numerous interactions with its binding pocket, and the excess of the photon energy is released through an anisotropic protein breathing motion in the direction of the extracellular space.

Here, the X-ray crystal structure of the β₁ adrenergic receptor, a G-protein-coupled receptor, bound to four small molecules that either act as full agonists or partial agonists is solved. The structures show that agonist binding induces a contraction of the catecholamine-binding pocket relative to the antagonist-bound receptor. This work reveals the pharmacological differences between different ligand classes, which should facilitate the structure-based design of new drugs with predictable efficacies.

This study solves the X-ray crystal structure of a constitutively active mutant of rhodopsin, a G-protein-coupled receptor, bound to a peptide derived from the C-terminus of the G protein transducin. Comparison of this structure with the structure of ground-state rhodopsin suggests how translocation of the retinal β-ionone ring leads to a rotational tilt of transmembrane helix 6, the critical conformational change that occurs upon activation.

Rhodospsin is a G-protein-coupled receptor that is responsible for vision in dim light. Light isomerizes the protein's retinal chromophore and triggers concerted movements of several transmembrane helices. Here, an approach involving mutant rhodopsins and infrared spectroscopy enabled changes in the electrostatic environment to be seen as rhodopsin proceeded along its activation pathway. Early conformational changes were observed that precede the well-known larger movements of the transmembrane helices.

Time-resolved serial crystallography at XFELs reveals ultrafast photochemical reactions, but high laser densities can cause photodamage to biological samples. Here, the authors study the early K-intermediate in bacteriorhodopsin at high power, showing overall conformation remains robust over a wide range.

The cryo-EM structure of the bovine rod CNG channel, isolated from retina, sheds light onto the structural basis for the subunit stoichiometry and reveals an additional gate within the ion conduction pathway contributed by the CNGB1 subunit.

A cryo-electron structure of the µ-opioid receptor in complex with the peptide agonist DAMGO and the inhibitory G protein G_i reveals structural determinants of its G protein-binding specificity.

Serial crystallography was developed for protein crystal data collection with X-ray free-electron lasers. Here the authors present several examples which show that serial crystallography using high-viscosity injectors can also be routinely employed for room-temperature data collection at synchrotrons.

High resolution structural information for G protein-coupled receptors has so far been limited to rhodopsin; here a crystal structure of the β₂AR adrenaline receptor is presented.

Although several X-ray crystal structures of G protein-coupled receptors (GPCRs) have been reported, relatively little is known about the conformational dynamics of these important membrane proteins; here, the authors used NMR spectroscopy to monitor the conformational changes that occur in the turkey β1-adrenergic receptor in the presence of antagonists, partial agonists, and full agonists.

The cellular functions of arrestins are determined in part by the pattern of phosphorylation on the G protein-coupled receptors (GPCRs) to which arrestins bind. Here, authors use a library of synthetic phosphopeptide analogues of the GPCR rhodopsin C-terminus and determine the ability of these peptides to bind and activate arrestins using a variety of biochemical and biophysical methods.

Crystallographic ‘snapshots’ taken at intervals of femtoseconds to milliseconds after activation show how a light-activated sodium pump carries sodium ions across the cell membrane.

Serial femtosecond crystallography using X-ray free-electron lasers has huge potential for time-resolved structural experiments. Here, the authors present a structure of the light-driven proton pump bacteriorhodopsin using these techniques.

The determination of high resolution structures of G protein coupled receptors (GPCRs) in complex with heterotrimeric G proteins is challenging. Here authors develop an antibody fragment, mAB16, which stabilizes GPCR/G-protein complexes and facilitates the application of high resolution cryo-EM.

Extensive mutant cycle analysis provides a map of the residues that contribute to stability and activation-associated conformational dynamics of the Gα_i1 protein in nucleotide-bound states and in complex with the G protein–coupled receptor rhodopsin.

Botulinum neurotoxin A (BoNT/A) is considered the most toxic substance known but is also used as a therapeutic drug for a growing number of diseases and conditions; researchers have now obtained a high-resolution crystal structure of the receptor-binding domain of the BoNT/A in complex with the luminal domain of synaptic vesicle protein 2C (SV2C), one of its receptors, allowing the identification of a peptide that can inhibit complex formation.

A highly conserved rearrangement of residue contacts functions as a common step in the activation pathways of diverse G-protein-coupled receptors.

A systematic investigation of high-resolution G-protein-coupled receptor (GPCR) structures uncovers a conserved inter-helical network of non-covalent contacts that defines the GPCR fold, and provides insights into the molecular determinants of different GPCR conformations.

Takashi Nagata et al. use UV-visible spectroscopic analysis to show that Ser186 increases the retinylidene Schiff base (SB) pKa of a spider rhodopsin in the inactive state but not after light activation. The change in contribution of Ser186 to the SB pKa suggests that the counterion (Glu181)–SB interaction rearranges upon light activation.