Visualization of arrestin recruitment by a G-protein-coupled receptor.

G-protein-coupled receptors (GPCRs) are critically regulated by ß-arrestins, which not only desensitize G-protein signalling but also initiate a G-protein-independent wave of signalling. A recent surge of structural data on a number of GPCRs, including the ß2 adrenergic receptor (ß2AR)-G-protein complex, has provided novel insights into the structural basis of receptor activation. However, complementary information has been lacking on the recruitment of ß-arrestins to activated GPCRs, primarily owing to challenges in obtaining stable receptor-ß-arrestin complexes for structural studies. Here we devised a strategy for forming and purifying a functional human ß2AR-ß-arrestin-1 complex that allowed us to visualize its architecture by single-particle negative-stain electron microscopy and to characterize the interactions between ß2AR and ß-arrestin 1 using hydrogen-deuterium exchange mass spectrometry (HDX-MS) and chemical crosslinking. Electron microscopy two-dimensional averages and three-dimensional reconstructions reveal bimodal binding of ß-arrestin 1 to the ß2AR, involving two separate sets of interactions, one with the phosphorylated carboxy terminus of the receptor and the other with its seven-transmembrane core. Areas of reduced HDX together with identification of crosslinked residues suggest engagement of the finger loop of ß-arrestin 1 with the seven-transmembrane core of the receptor. In contrast, focal areas of raised HDX levels indicate regions of increased dynamics in both the N and C domains of ß-arrestin 1 when coupled to the ß2AR. A molecular model of the ß2AR-ß-arrestin signalling complex was made by docking activated ß-arrestin 1 and ß2AR crystal structures into the electron microscopy map densities with constraints provided by HDX-MS and crosslinking, allowing us to obtain valuable insights into the overall architecture of a receptor-arrestin complex. The dynamic and structural information presented here provides a framework for better understanding the basis of GPCR regulation by arrestins.

Ligand-regulated oligomerization of beta(2)-adrenoceptors in a model lipid bilayer.

The beta(2)-adrenoceptor (beta(2)AR) was one of the first Family A G protein-coupled receptors (GPCRs) shown to form oligomers in cellular membranes, yet we still know little about the number and arrangement of protomers in oligomers, the influence of ligands on the organization or stability of oligomers, or the requirement for other proteins to promote oligomerization. We used fluorescence resonance energy transfer (FRET) to characterize the oligomerization of purified beta(2)AR site-specifically labelled at three different positions with fluorophores and reconstituted into a model lipid bilayer. Our results suggest that the beta(2)AR is predominantly tetrameric following reconstitution into phospholipid vesicles. Agonists and antagonists have little effect on the relative orientation of protomers in oligomeric complexes. In contrast, binding of inverse agonists leads to significant increases in FRET efficiencies for most labelling pairs, suggesting that this class of ligand promotes tighter packing of protomers and/or the formation of more complex oligomers by reducing conformational fluctuations in individual protomers. The results provide new structural insights into beta(2)AR oligomerization and suggest a possible mechanism for the functional effects of inverse agonists.

[Relationship Between Urban Spatial Pattern and Thermal Environment Response in Summer: A Case Study of Hefei City].

With the continuous expansion of cities, the land cover type of the region is transformed, a large number of natural landscapes are replaced by man-made landscapes, and the environmental temperature rises. The study of the response relationship between urban spatial pattern and thermal environment provides some guidance for improving the ecological environment and optimizing the urban spatial layout. Based on the Landsat 8 series remote sensing image data of Hefei City in 2020 and analysis platforms such as ENVI and ARCGIS, Pearson correlation and profile lines were used to reflect the correlation between the two. Then, the three spatial pattern components with the greatest correlation were selected to construct multiple regression functions to investigate the influence of urban spatial pattern on urban thermal environment and its mechanism of action. The results showed that:① the high temperature area of Hefei City increased significantly with the advance of time during 2013-2020. For different seasons, the urban heat island effect showed that summer>autumn>spring>winter. ② In the central urban area, the building occupancy, building height, imperviousness occupancy, and population density were significantly higher than those in the suburbs, whereas fractional vegetation coverage presented a higher suburban than urban area and mainly showed a point distribution in the urban area and an irregular distribution of water bodies. ③ The urban high-temperature zone was mainly distributed in various development zones in urban areas, whereas other places in urban areas were dominated by medium-high temperature and above-temperature zoning, and suburban areas were dominated by medium-low temperature. ④ The Pearson coefficients between the spatial pattern of each element and the thermal environment were positively correlated with the building occupancy (0.395), impervious surface occupancy (0.333), population density (0.481), and building height (0.188) and negatively correlated with fractional vegetation coverage (-0.577) and water occupancy (-0.384). The coefficients of the constructed multiple regression functions, including building occupancy, population density, and fractional vegetation coverage, were 8.372, 0.295, and -5.639 respectively, with a constant of 38.555. The results of this study can provide a reference basis for optimizing urban spatial layouts and improving urban living quality.

The effect of ligand efficacy on the formation and stability of a GPCR-G protein complex.

G protein-coupled receptors (GPCRs) mediate the majority of physiologic responses to hormones and neurotransmitters. However, many GPCRs exhibit varying degrees of agonist-independent G protein activation. This phenomenon is referred to as basal or constitutive activity. For many of these GPCRs, drugs classified as inverse agonists can suppress basal activity. There is a growing body of evidence that basal activity is physiologically relevant, and the ability of a drug to inhibit basal activity may influence its therapeutic properties. However, the molecular mechanism for basal activation and inhibition of basal activity by inverse agonists is poorly understood and difficult to study, because the basally active state is short-lived and represents a minor fraction of receptor conformations. Here, we investigate basal activation of the G protein Gs by the beta(2) adrenergic receptor (beta(2)AR) by using purified receptor reconstituted into recombinant HDL particles with a stoichiometric excess of Gs. The beta(2)AR is site-specifically labeled with a small, environmentally sensitive fluorophore enabling direct monitoring of agonist- and Gs-induced conformational changes. In the absence of an agonist, the beta(2)AR and Gs can be trapped in a complex by enzymatic depletion of guanine nucleotides. Formation of the complex is enhanced by the agonist isoproterenol, and it rapidly dissociates on exposure to concentrations of GTP and GDP found in the cytoplasm. The inverse agonist ICI prevents formation of the beta(2)AR-Gs complex, but has little effect on preformed complexes. These results provide insights into G protein-induced conformational changes in the beta(2)AR and the structural basis for ligand efficacy.

Acupuncture Reduces the Risk of Dysphagia in Stroke Patients: A Propensity Score-Matched Cohort Study.

Background: Post-stroke dysphagia (PSD) affects the quality of life in stroke patients, impairs their rehabilitation ability, and causes other complications following stroke. Currently, there is currently some understanding of PSD risk factors, but its protective factors remain largely unknown. Objective: To analyze the effects of acupuncture (AP) on dysphagia in stroke patients and explore its potential as a preventive therapy. Methods: Patients with a diagnosis of stroke from 2010 to 2019 were selected and followed until 2020, utilizing factors such as age, gender, stroke location, stroke type, and baseline comorbidity. To compare the incidence of dysphagia, equal numbers of stroke patients treated with and without AP (n = 1,809) were matched by 1:1 propensity scoring. The Cox proportional hazards model and Kaplan-Meier method were used to assess the risk of dysphagia as an outcome measure. Results: The stroke patients treated with AP had a lower risk of dysphagia after adjusting for age, gender, stroke location, stroke type, and baseline comorbidity [adjusted hazard ratio (AHR) = 0.43, 95% confidence interval = 0.37-0.49] compared with those in the non-AP cohort. AP also decreased the risk of PSD among different gender groups. The risk ratios were AHR = 0.45 and AHR = 0.33 for males and females, respectively. AP also reduced the risk for PSD among different age groups. The risk ratios were AHR = 0.20, AHR = 0.37, AHR = 0.41, and AHR = 0.45 for the 18-39, 40-59, 60-79, and >80 years-old groups. Regarding stroke types (ischemic, hemorrhagic, and mixed type), patients treated with AP had a lower risk (AHR = 0.47, 0.28 and 0.17, respectively). With respect to stroke location, the risk of PSD in AP-treated patients was decreased regardless of location: brain stem (AHR = 0.41), diencephalon (AHR = 0.13), or multiple lesions (AHR = 0.40), the risk of PSD in AP-treated patients was decreased. For all baseline comorbidities, AP attenuated the risk of dysphagia. The cumulative incidence of dysphagia was remarkably lower in the AP group than in the non-AP group (log-rank test, P = 0.000). Limitations: First, this was a single-center clinical retrospective study. Second, we did not classify the severity of stroke and dysphagia. Third, all data were extracted manually. Lastly, the sample size was relatively small. Thus, future studies with larger sample sizes are warranted to verify our findings. Conclusion: Acupuncture treatment attenuates the risk of dysphagia in stroke patients. Future research should increase the sample size and elaborate further on the details of the AP protocol.

Conformational dynamics of single G protein-coupled receptors in solution.

G protein-coupled receptors (GPCRs) comprise a large family of seven-helix transmembrane proteins which regulate cellular signaling by sensing light, ligands, and binding proteins. The GPCR activation process, however, is not a simple on-off switch; current models suggest a complex conformational landscape in which the active, signaling state includes multiple conformations with similar downstream activity. The present study probes the conformational dynamics of single ß(2)-adrenergic receptors (ß(2)ARs) in the solution phase by Anti-Brownian ELectrokinetic (ABEL) trapping. The ABEL trap uses fast electrokinetic feedback in a microfluidic configuration to allow direct observation of a single fluorescently labeled ß(2)AR for hundreds of milliseconds to seconds. By choosing a reporter dye and labeling site sensitive to ligand binding, we observe a diversity of discrete fluorescence intensity and lifetime levels in single ß(2)ARs, indicating a varying radiative lifetime and a range of discrete conformational states with dwell times of hundreds of milliseconds. We find that the binding of agonist increases the dwell times of these states, and furthermore, we observe millisecond fluctuations within states. The intensity autocorrelations of these faster fluctuations are well-described by stretched exponential functions with a stretching exponent ß ~ 0.5, suggesting protein dynamics over a range of time scales.

GPCR engineering yields high-resolution structural insights into beta2-adrenergic receptor function.

The beta2-adrenergic receptor (beta2AR) is a well-studied prototype for heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) that respond to diffusible hormones and neurotransmitters. To overcome the structural flexibility of the beta2AR and to facilitate its crystallization, we engineered a beta2AR fusion protein in which T4 lysozyme (T4L) replaces most of the third intracellular loop of the GPCR ("beta2AR-T4L") and showed that this protein retains near-native pharmacologic properties. Analysis of adrenergic receptor ligand-binding mutants within the context of the reported high-resolution structure of beta2AR-T4L provides insights into inverse-agonist binding and the structural changes required to accommodate catecholamine agonists. Amino acids known to regulate receptor function are linked through packing interactions and a network of hydrogen bonds, suggesting a conformational pathway from the ligand-binding pocket to regions that interact with G proteins.

A monoclonal antibody for G protein-coupled receptor crystallography.

G protein-coupled receptors (GPCRs) constitute the largest family of signaling proteins in mammals, mediating responses to hormones, neurotransmitters, and senses of sight, smell and taste. Mechanistic insight into GPCR signal transduction is limited by a paucity of high-resolution structural information. We describe the generation of a monoclonal antibody that recognizes the third intracellular loop (IL3) of the native human beta(2) adrenergic (beta(2)AR) receptor; this antibody was critical for acquiring diffraction-quality crystals.