G protein-coupled receptors (GPCRs) signal primarily through G proteins or arrestins. Arrestin binding to GPCRs blocks G protein interaction and redirects signaling to numerous G proteinindependent pathways. Here we report the crystal structure of a constitutively active form of human rhodopsin bound to a pre-activated form of the mouse visual arrestin, determined by serial femtosecond X-ray laser crystallography. Together with extensive biochemical and mutagenesis data, the structure reveals an overall architecture of the rhodopsin-arrestin assembly, in which rhodopsin uses distinct structural elements, including TM7 and Helix 8 to recruit arrestin. Correspondingly, arrestin adopts the pre-activated conformation, with a ~20° rotation between the Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:http://www.nature.com/authors/editorial_policies/license.html#terms § Correspondence to H. Eric Xu: Eric.Xu@vai.org. * These authors contributed equally.Contributions: Y.K. initiated the project, developed the expression and purification methods for rhodopsin-arrestin complex, and bulk-purified expression constructs and proteins used in LCP crystallization for the SFX method; X.E.Z. collected the synchrotron data, helped with the SFX data collection, processed the data, and solved the structures; X.G. expressed and purified rhodopsinarrestin complexes, characterized their binding and thermal stability, discovered the initial crystallization conditions with 9.7 MAG, prepared most crystals for synchrotron data collection, prepared all crystals for the final data collection by SFX, helped with SFX data collection, and established the initial cross-linking method for the rhodopsin-arrestin complex; Y.H. designed and performed Tango assays and disulfide bond cross-linking experiments; C.Z. developed the mammalian expression methods; P.W.dW helped with XFEL data processing and performed computational experiments; J.K., M.H.E.T., K. M. S-P., K. P., J. M., Y.J., X.Y.Z., and Q.C. performed cell culture, mutagenesis, protein purification, rhodopsin-arrestin binding experiments; W.L. and A.I. grew crystals and collected synchrotron data at APS and SFX data at LCLS, G.W.H. and Q.X. determined and validated the structure. Z.Z. and V.K. constructed the full model, the phosphorylated rhodopsin-arrestin model, and help writing the paper; D.W., S.L., D.J., C.K., Sh.B., and N.A. Z. helped with XFEL data collection and initial data analysis; S.B., M.M., and G.J.W. set up the XFEL experiment, performed the data collection, and commented on the paper. A.B., T.W., C.G., O.Y., and H.C. helped with XFEL data collection and data analysis, processed the data and helped with structure validation. G.M. W., B.P., and P.G. performed HDX experiments and helped with manuscript writing. J.L. helped initiate this collaborative project and with writing the paper. M.W. collected the 7.7 Å dataset at Swiss Light Source. A.M.,...

Serotonin or 5-hydroxytryptamine (5-HT) regulates a wide spectrum of human physiology through the 5-HT receptor family. We report the crystal structures of the human 5-HT1B G protein-coupled receptor bound to the agonist anti-migraine medications ergotamine and dihydroergotamine. The structures reveal similar binding modes for these ligands, which occupy the orthosteric pocket and an extended binding pocket close to the extracellular loops. The orthosteric pocket is formed by residues conserved in the 5-HT receptor family, clarifying the family-wide agonist activity of 5-HT. Compared to the accompanying structure of the 5-HT2B receptor, the 5-HT1B receptor displays a 3 angstrom outward shift at the extracellular end of helix V, resulting in a more open extended pocket that explains subtype selectivity. Together with docking and mutagenesis studies, these structures provide a comprehensive structural basis for understanding receptor-ligand interactions and designing subtype-selective serotonergic drugs.

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A common feature of nuclear receptor ligand binding domains (LBD) is a helical sandwich fold that nests a ligand binding pocket within the bottom half of the domain. Here we report that the ligand pocket of glucocorticoid receptor (GR) can be continuously extended into the top half of the LBD by binding to deacylcortivazol (DAC), an extremely potent glucocorticoid. It has been puzzling for decades why DAC, which contains a phenylpyrazole replacement at the conserved 3-ketone of steroid hormones that are normally required for activation of their cognate receptors, is a potent GR activator. The crystal structure of the GR LBD bound to DAC and the fourth LXXLL motif of steroid receptor coactivator 1 reveals that the GR ligand binding pocket is expanded to a size of 1,070 Å 3 , effectively doubling the size of the GR dexamethasone-binding pocket of 540 Å 3 and yet leaving the structure of the coactivator binding site intact. DAC occupies only ϳ50% of the space of the pocket but makes intricate interactions with the receptor around the phenylpyrazole group that accounts for the high-affinity binding of DAC. The dramatic expansion of the DAC-binding pocket thus highlights the conformational adaptability of GR to ligand binding. The new structure also allows docking of various nonsteroidal ligands that cannot be fitted into the previous structures, thus providing a new rational template for drug discovery of steroidal and nonsteroidal glucocorticoids that can be specifically designed to reach the unoccupied space of the expanded pocket.Glucocorticoid receptor (GR) is a steroid hormone-regulated transcription factor that belongs to the nuclear receptor superfamily (1, 39). Upon ligand binding, GR regulates expression of an array of genes involved in glucose and lipid metabolism, bone turnover, lung maturation, and homeostasis of the immune, cardiovascular, and central nervous systems. GR ligands, including dexamethasone (DEX), fluticasone propionate, and other steroid analogs, are among the most effective agents for treating asthma, arthritis, leukemia, and various autoimmune diseases because of their potent anti-inflammatory and immunosuppressive effects. However, therapeutic use of glucocorticoids also induces a number of side effects including diabetes, bone loss, hypertension, and obesity (24). Although the molecular basis for these undesired side effects remains to be fully characterized (26), development of a GR ligand that can dissociate the therapeutic effects from the undesired adverse effects has been the subject of intense pharmaceutical research (23,25).The transcriptional function of GR is primarily controlled by ligand binding to its C-terminal ligand binding domain (LBD). In the absence of ligand, GR is retained in the cytoplasm by an association between the receptor LBD and the HSP90 chaperone complex (22). Ligand binding induces conformational changes in the LBD that lead to translocation of the receptor into the nucleus, where GR binds to DNA and regulates transcription of nearby genes. In addition to ...

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BackgroundAlthough laparoscopic surgery has been recommended as an optional therapy for patients with early gastric cancer, whether patients with locally advanced gastric cancer (AGC) could benefit from laparoscopy-assisted distal gastrectomy (LADG) with D2 lymphadenectomy remains elusive due to a lack of comprehensive clinical data. To evaluate the efficacy of LADG, we conducted a multi-institutional randomized controlled trial to compare laparoscopy-assisted versus open distal gastrectomy (ODG) for AGC in North China.MethodsIn this RCT, after patients were enrolled according to the eligibility criteria, they were preoperatively assigned to LADG or ODG arm randomly with a 1:1 allocation ratio. The primary endpoint was the morbidity and mortality within 30 postoperative days to evaluate the surgical safety of LADG. The secondary endpoint was 3-year disease-free survival. This trial was registered at ClinicalTrial.gov as NCT02464215.ResultsBetween March 2014 and August 2017, a total of 446 patients with cT2-4aN0-3M0 (AJCC 7th staging system) were enrolled. Of these, 222 patients underwent LADG and 220 patients underwent ODG were included in the modified intention-to-treat analysis. The compliance rate of D2 lymph node dissection was identical between the LADG and ODG arms (99.5%, P = 1.000). No significant difference was observed regarding the overall postoperative complication rate in two groups (LADG 13.1%, ODG 17.7%, P = 0.174). No operation-related death occurred in both arms.ConclusionsThis trial confirmed that LADG performed by credentialed surgeons was safe and feasible for patients with AGC compared with conventional ODG.

Pituitary adenylate cyclase activating polypeptide (PACAP) is a member of the PACAP/glucagon family of peptide hormones, which controls many physiological functions in the immune, nervous, endocrine, and muscular systems. It activates adenylate cyclase by binding to its receptor, PAC1R, a member of class B G-protein coupled receptors (GPCR). Crystal structures of a number of Class B GPCR extracellular domains (ECD) bound to their respective peptide hormones have revealed a consensus mechanism of hormone binding. However, the mechanism of how PACAP binds to its receptor remains controversial as an NMR structure of the PAC1R ECD/PACAP complex reveals a different topology of the ECD and a distinct mode of ligand recognition. Here we report a 1.9 Å crystal structure of the PAC1R ECD, which adopts the same fold as commonly observed for other members of Class B GPCR. Binding studies and cell-based assays with alanine-scanned peptides and mutated receptor support a model that PAC1R uses the same conserved fold of Class B GPCR ECD for PACAP binding, thus unifying the consensus mechanism of hormone binding for this family of receptors.

Laparoscopic surgery is an acceptable alternative to open surgery in colorectal cancer treatment. However, in gastric cancer, there is not much scientific evidence. Here, we proposed a prospective randomized clinical trial to evaluate the radicalness and safety of laparoscopic D2 dissection for gastric cancer. From October 2010 to September 2012, 300 patients with gastric cancer were randomized to undergo either laparoscopy-assisted gastrectomy (LAG) or conventional open gastrectomy (OG) with D2 dissection. Clinicopathological parameters, recovery and complications were compared between these two groups. Thirty cases were excluded because of refusing to be involved in the trial, having peritoneal seeding metastasis or LAG conversed to OG, and finally 270 cases were analyzed (128 in LAG and 142 in OG). No significant differences were observed in gender, age, body mass index, stages and types of radical resection [radical proximal gastrectomy (PG + D2), radical distal gastrectomy (DG + D2) and radical total gastrectomy (TG + D2)] (P > 0.05). The number of harvested lymph nodes (HLNs) was similar (29.3 ± 11.8 in LAG vs. 30.1 ± 11.4 in OG, P = 0.574). And in the same type of radical resection, no significant difference was found in the number of HLNs between the two groups (PG + D2, P = 0.770; DG + D2, P = 0.500; TG + D2, P = 0.993). The morbidity of the LAG group (21.8 %) was also comparable to the OG group (19.0 %, P = 0.560). However, the LAG group had significantly less blood loss and faster recovery, and a longer operation time (P < 0.05). Laparoscopic D2 dissection is feasible, safe and capable of fulfilling oncologic criteria for the treatment of gastric cancer.