The Roles of Transmembrane Domain Helix-III during Rhodopsin Photoactivation

Background: Rhodopsin, the prototypic member of G protein-coupled receptors (GPCRs), undergoes isomerization of 11- cis-retinal to all-trans-retinal upon photoactivation. Although the basic mechanism by which rhodopsin is activated is well understood, the roles of whole transmembrane (TM) helix-III during rhodopsin photoactivation in detail are not completely clear. Principal Findings: We herein use single-cysteine mutagenesis technique to investigate conformational changes in TM helices of rhodopsin upon photoactivation. Specifically, we study changes in accessibility and reactivity of cysteine residues introduced into the TM helix-III of rhodopsin. Twenty-eight single-cysteine mutants of rhodopsin (P107C-R135C) were prepared after substitution of all natural cysteine residues (C140/C167/C185/C222/C264/C316) by alanine. The cysteine mutants were expressed in COS-1 cells and rhodopsin was purified after regeneration with 11-cis-retinal. Cysteine accessibility in these mutants was monitored by reaction with 4, 49-dithiodipyridine (4-PDS) in the dark and after illumination. Most of the mutants except for T108C, G109C, E113C, I133C, and R135C showed no reaction in the dark. Wide variation in reactivity was observed among cysteines at different positions in the sequence 108–135 after photoactivation. In particular, cysteines at position 115, 119, 121, 129, 131, 132, and 135, facing 11-cis-retinal, reacted with 4-PDS faster than neighboring amino acids. The different reaction rates of mutants with 4-PDS after photoactivation suggest that the amino acids in different positions in helix-III are exposed to aqueous environment to varying degrees. Significance: Accessibility data indicate that an aqueous/hydrophobic boundary in helix-III is near G109 and I133. The lack of reactivity in the dark and the accessibility of cysteine after photoactivation indicate an increase of water/4-PDS accessibility for certain cysteine-mutants at Helix-III during formation of Meta II. We conclude that photoactivation resulted in water-accessible at the chromophore-facing residues of Helix-III.National Institutes of Health (U.S.) (grant GM28289)National Eye Institute (Grant Grant EY11716)National Science Foundation (U.S.) (grant EIA-0225609

Ligand-Dependent Conformations and Dynamics of the Serotonin 5-HT2A Receptor Determine Its Activation and Membrane-Driven Oligomerization Properties

From computational simulations of a serotonin 2A receptor (5-HT2AR) model complexed with pharmacologically and structurally diverse ligands we identify different conformational states and dynamics adopted by the receptor bound to the full agonist 5-HT, the partial agonist LSD, and the inverse agonist Ketanserin. The results from the unbiased all-atom molecular dynamics (MD) simulations show that the three ligands affect differently the known GPCR activation elements including the toggle switch at W6.48, the changes in the ionic lock between E6.30 and R3.50 of the DRY motif in TM3, and the dynamics of the NPxxY motif in TM7. The computational results uncover a sequence of steps connecting these experimentally-identified elements of GPCR activation. The differences among the properties of the receptor molecule interacting with the ligands correlate with their distinct pharmacological properties. Combining these results with quantitative analysis of membrane deformation obtained with our new method (Mondal et al, Biophysical Journal 2011), we show that distinct conformational rearrangements produced by the three ligands also elicit different responses in the surrounding membrane. The differential reorganization of the receptor environment is reflected in (i)-the involvement of cholesterol in the activation of the 5-HT2AR, and (ii)-different extents and patterns of membrane deformations. These findings are discussed in the context of their likely functional consequences and a predicted mechanism of ligand-specific GPCR oligomerization

Changes in HbA1c, body weight, and systolic blood pressure in type 2 diabetes patients initiating dapagliflozin therapy: a primary care database study

Markus F Scheerer,1 Roland Rist,1 Orm Proske,1 Annika Meng,2 Karel Kostev2 1Medical Department, AstraZeneca GmbH, Wedel, Germany; 2IMS Health GmbH & Co. OHG, Frankfurt am Main, Germany Aims: To investigate changes in glycated hemoglobin (HbA1c), body weight (BW), and systolic blood pressure (SBP) in type 2 diabetes (T2D) primary care patients initiating dapagliflozin treatment. Methods: T2D patients who started dapagliflozin in 985 general and 32 diabetologist practices (Disease Analyzer, Germany: December 2012–October 2014) were analyzed (3- and 6-month follow-up). Multivariate linear regression analyses were used to identify clinical characteristics and comorbidity associated with changes in HbA1c, BW, and SBP. Results: The study included 1,169 T2D patients (age: 62.5 years; men: 59.3%; diabetologist care: 23%) with newly initiated dapagliflozin therapy. At the 3-month stage, dapagliflozin significantly reduced HbA1c (−0.8%±1.4%) compared to the baseline (8.5%±1.5%) (P<0.001). Changes were maintained after 6 months (−0.8%±1.5%) (P<0.001). Patients with high baseline HbA1c values (>9%) showed greater reductions in HbA1c than the overall sample (3 months −1.8%, 6 months −1.8%; both P<0.05). BW and SBP also showed statistically significant reductions with dapagliflozin over 3 and 6 months (−2.2 kg, P<0.001; −2.2 mmHg, P=0.003 and −2.5 kg, P<0.001; −2.3 mmHg, P=0.011, respectively). After 3 months, 53% of patients achieved a reduction in both HbA1c and BW; the same holds true for 45% of patients at the 6-month mark. Similar results were observed both in general and diabetologist practices. In multivariate analyses, baseline HbA1c (parameter estimate: −0.6479) and diabetologist care (−0.2553) were independent predictors of HbA1c change (6 months) (all P<0.05). Conclusion: T2D patients treated with dapagliflozin therapy achieved statistically significant reductions in HbA1c, BW, and SBP in a real-world primary and diabetologist care setting. The changes were comparable to the results of the dapagliflozin clinical trial program. Keywords: type 2 diabetes, dapagliflozin, HbA1c, body mass index, systolic blood pressure&nbsp