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The histamine H4 receptor (H4R) plays key role in immune cell function and is a highly valued target for treating allergic and inflammatory diseases. However, structural information of H4R remains elusive. Here, we report four cryo-EM structures of H4R/Gi complexes, with either histamine or synthetic agonists clobenpropit, VUF6884 and clozapine bound. Combined with mutagenesis, ligand binding and functional assays, the structural data reveal a distinct ligand binding mode where D943.32 and a π-π network determine the orientation of the positively charged group of ligands, while E1825.46, located at the opposite end of the ligand binding pocket, plays a key role in regulating receptor activity. The structural insight into H4R ligand binding allows us to identify mutants at E1825.46 for which the agonist clobenpropit acts as an inverse agonist and to correctly predict inverse agonism of a closely related analog with nanomolar potency. Together with the findings regarding receptor activation and Gi engagement, we establish a framework for understanding H4R signaling and provide a rational basis for designing novel antihistamines targeting H4R.The histamine H4 receptor (H4R) plays key roles in immune cell function. Here, the authors report structures of H4R-Gi complex with various ligands bound, revealing distinct ligand binding modes and a basis for rational design of novel antihistamines targeting H4R. [ABSTRACT FROM AUTHOR]

Biodiversity is sensitive to climate change and human activity. Grazing management practices have a profound impact on plant species–genetic diversity in grassland and woodland communities. In this study, we explored the responses of species and genetic diversity to grazing in Ulmus pumila L. communities in the Hunshandak Sandy Land, analyzed the relationship between species and genetic diversity, and revealed the effects of climate factors on them. We found that the dominant species were Spiraea trilobata, Caragana microphylla and Artemisia intramongolica in U. pumila communities. Plant species richness in the banned grazing (BG) and seasonal grazing (SG) communities was significantly higher than that in the delayed grazing (DG) community. Plant Simpson's diversity index showed a downward trend with increasing grazing duration. There was no difference in allelic richness in nuclear DNA (nrDNA) of U (U. pumila) and chloroplast DNA (cpDNA) of NU (other dominant species besides U. pumila) among grazing management types. The expected heterozygosity of U in nrDNA and cpDNA was significantly affected by grazing management, and the trend was BG > SG > DG. The genetic diversity of U was lower than that of NU. The genetic diversity characteristics of U in cpDNA were lower than those in nrDNA. The analysis of molecular variance (AMOVA) showed that 98.08% of the variation in U and 95.25% of the variation in NU was attributed within populations and the differences within grazing management types were 13.35% in U and 24.08% in NU (p < 0.001). The species richness of communities was positively correlated with the genetic diversity of U, NU and all dominant species (U + NU) in communities. The nineteen climatic variables together explained 94.24% and 79.08% of the total variation in U and NU genetic and species diversity. The mean temperature of the warmest quarter and temperature seasonality were the main factors affecting genetic diversity (p = 0.046; 0.01), while the maximum temperature of the warmest month was the main factor affecting species diversity (p = 0.05). [ABSTRACT FROM AUTHOR]

Seeds are generally sensitive to environmental change and the reactive oxygen species (ROS) generated during their development cause oxidative stress leading to oxidative damage in seeds. Therefore, it is essential to understand the physiological and biochemical changes associated with seed development. The seeds physiological responses of Artemisia scoparia, Lespedeza davurica, and Cleistogenes squarrosa to simulated warming and rainfall reduction in sandy grassland were studied. The seed malondialdehyde (MDA) and proline content of C. squarrosa was significantly affected by warming. The rainfall reduction obviously impacted the proline level of three plants. However, the combined stress of warming and drought had no significant effect on the seed MDA and proline contents of three psammophytes. With decreasing rainfall gradient in natural temperature, seed MDA and proline content were increased by 50.0 and 49.8% in A. scoparia and 30.8% and 41.3% in C. squarrosa, respectively. When precipitation was reduced by 60%, the increasing values were A. scoparia > L. davurica > C. squarrosa. The separate effects of warming and drought had an obvious influence on the seed enzyme activity of A. scoparia, but only significantly affected the seed peroxidase (POD) activity of L. davurica, while the combined effect of two factors had no significant effect on many seed enzyme activities of three psammophytes. Whether it's warming or not, more than 40% precipitation deficit had a great influence on seed cellular superoxide dismutase (SOD) activity of L. davurica and C. squarrosa, and the increase of seed SOD activity in C. squarrosa is greater than that of L. davurica. At natural temperature, higher than 40% rainfall reduction had a significant influence on seed POD activity of three psammophytes, and compared with the natural precipitation, with descending order was A. scoparia > L. davurica > C. squarrosa. The variation trend of seed catalase (CAT) of C. squarrosa under severe water deficit stress was decreased by 94.4%, and opposite to that of A. scoparia under combined effect of warming and precipitation reduction, increased by 73.0%. Correlation result indicated that temperature (T) was significant in A. scoparia and C. squarrosa, precipitation (W) was significant in L. davurica based on the Monte Carlo test (p = 0.034, 0.028, 0.016). [ABSTRACT FROM AUTHOR]

Lysophosphatidylserine (LysoPS) is a lipid mediator that induces multiple cellular responses through binding to GPR174. Here, we present the cryo-electron microscopy (cryo-EM) structure of LysoPS-bound human GPR174 in complex with Gs protein. The structure reveals a ligand recognition mode, including the negatively charged head group of LysoPS forms extensive polar interactions with surrounding key residues of the ligand binding pocket, and the L-serine moiety buries deeply into a positive charged cavity in the pocket. In addition, the structure unveils a partially open pocket on transmembrane domain helix (TM) 4 and 5 for a lateral entry of ligand. Finally, the structure reveals a Gs engaging mode featured by a deep insertion of a helix 5 (αH5) and extensive polar interactions between receptor and αH5. Taken together, the information revealed by our structural study provides a framework for understanding LysoPS signaling and a rational basis for designing LysoPS receptor-targeting drugs. GPR174 is a lysophosphatidylserine (LysoPS) activated GPCR. Here, the authors report the cryo-EM structure of LysoPS-bound human GPR174 in complex with Gs protein. The study reveals how GPR174 recognizes the lipid ligand and engages Gs in a distinct binding mode. [ABSTRACT FROM AUTHOR]

Adhesion G protein-coupled receptors (aGPCRs) are keys of many physiological events and attractive targets for various diseases. aGPCRs are also known to be capable of self-activation via an autoproteolysis process that removes the inhibitory GAIN domain on the extracellular side of receptor and releases a stalk peptide to bind and activate the transmembrane side of receptor. However, the detailed mechanism of aGPCR activation remains elusive. Here, we report the cryo-electron microscopy structures of GPR110 (ADGRF1), a member of aGPCR, in complex with Gq, Gs, Gi, G12 and G13. The structures reveal distinctive ligand engaging model and activation conformations of GPR110. The structures also unveil the rarely explored GPCR/G12 and GPCR/G13 engagements. A comparison of Gq, Gs, Gi, G12 and G13 engagements with GPR110 reveals details of G-protein engagement, including a dividing point at the far end of the alpha helix 5 (αH5) of Gα subunit that separates Gq/Gs engagements from Gi/G12/G13 engagements. This is also where Gq/Gs bind the receptor through both hydrophobic and polar interaction, while Gi/G12/G13 engage receptor mainly through hydrophobic interaction. We further provide physiological evidence of GPR110 activation via stalk peptide. Taken together, our study fills the missing information of GPCR/G-protein engagement and provides a framework for understanding aGPCR activation and GPR110 signaling. aGPCRs play key roles in multiple physiological processes. Here the authors report cryo-EM structures of GPR110 in complexes with Gq, Gs, Gi, G12 and G13 protein to reveal a detailed mechanism of aGPCR activation via the tethered stalk peptide and principles of G-protein coupling and selectivity on GPR110. [ABSTRACT FROM AUTHOR]

Leukotriene B4 receptor 1 (BLT1) plays crucial roles in the acute inflammatory responses and is a valuable target for anti-inflammation treatment, however, the mechanism by which leukotriene B4 (LTB4) activates receptor remains unclear. Here, we report the cryo-electron microscopy (cryo-EM) structure of the LTB4 -bound human BLT1 in complex with a Gi protein in an active conformation at resolution of 2.91 Å. In combination of molecule dynamics (MD) simulation, docking and site-directed mutagenesis, our structure reveals that a hydrogen-bond network of water molecules and key polar residues is the key molecular determinant for LTB4 binding. We also find that the displacement of residues M1013.36 and I2717.39 to the center of receptor, which unlock the ion lock of the lower part of pocket, is the key mechanism of receptor activation. In addition, we reveal a binding site of phosphatidylinositol (PI) and discover that the widely open ligand binding pocket may contribute the lack of specificity and efficacy for current BLT1-targeting drug design. Taken together, our structural analysis provides a scaffold for understanding BLT1 activation and a rational basis for designing anti-leukotriene drugs. In the paper, Dr. Wang et al reported a cryo-EM structure of the human leukotriene B4 receptor 1 (BLT1) in complex with its native ligand leukotriene B4 (LTB4) in an active conformation complexed with Gi protein. The structure reveals the molecule determinant of LTB4 binding and the mechanism of receptor activation. These structural information will boost the understanding of LTB4-BLT1 signaling and provide a rational basis for designing novel anti-leukotriene drugs. [ABSTRACT FROM AUTHOR]

Extensive studies have shown that the success of invasive plants in large environmental gradients can be partly attributed to related factors, including phenotypic plasticity and rapid evolution. To enhance their ability to compete and invade, invasive plants often show higher morphological and physiological plasticity to adapt to different habitat conditions. In the past two decades, invasive species have expanded to some new habitats in North and Northwest China, including arid oasis agricultural zones, which are disturbed by human activities, and the ecosystem itself is very fragile. To evaluate the ecological adaptability of invasive plants widely distributed in North and Northwest China, we studied the physiological response and tolerance mechanism of different geographical populations of Solanum rostratum Dunal to different drought-stress gradients in extremely arid regions (Xinjiang population) and semi-arid regions (Inner Mongolia population). The results showed that with the aggravation of drought stress, S. rostratum from different geographical populations adopted different physiological mechanisms to drought stress. Xinjiang population was mostly affected by root/shoot ratio and chlorophyll fluorescence characteristics, showing higher plasticity in the net and total photosynthetic rates, while the Inner Mongolia population mainly relied on the accumulation of osmotic adjustment substances, higher leaf dry matter content, and increased malondialdehyde to cope with drought stress. Based on these results, we concluded that the physiological responses of S. rostratum invading different habitats in northern China to drought stress were significantly different. The drought resistance of the Xinjiang population was higher than that of the Inner Mongolia population. In general, S. rostratum can be widely adapted to both harsh and mild habitats through phenotypic plasticity, threatening agricultural production and ecological environment security in northern China. [ABSTRACT FROM AUTHOR]

Histamine receptors play important roles in various pathophysiological conditions and are effective targets for anti-allergy treatment, however the mechanism of receptor activation remain elusive. Here, we present the cryo-electron microscopy (cryo-EM) structure of the human H1R in complex with a Gq protein in an active conformation via a NanoBiT tethering strategy. The structure reveals that histamine activates receptor via interacting with the key residues of both transmembrane domain 3 (TM3) and TM6 to squash the binding pocket on the extracellular side and to open the cavity on the intracellular side for Gq engagement in a model of "squash to activate and expand to deactivate". The structure also reveals features for Gq coupling, including the interaction between intracellular loop 2 (ICL2) and the αN-β junction of Gq/11 protein. The detailed analysis of our structure will provide a framework for understanding G-protein coupling selectivity and clues for designing novel antihistamines. Histamine receptors are effective targets for allergy treatments and antihistamines are the first choice of many allergic disorders, but the exact mechanism of agonist binding and receptor activation remain unknown. Here, the authors present the cryo-EM structure of histamine-bound H1R/Gq complex and propose a mechanism of ligand induced receptor activation. [ABSTRACT FROM AUTHOR]

Frizzled receptors (FZDs) are class-F G-protein-coupled receptors (GPCRs) that function in Wnt signalling and are essential for developing and adult organisms1,2. As central mediators in this complex signalling pathway, FZDs serve as gatekeeping proteins both for drug intervention and for the development of probes in basic and in therapeutic research. Here we present an atomic-resolution structure of the human Frizzled 4 receptor (FZD4) transmembrane domain in the absence of a bound ligand. The structure reveals an unusual transmembrane architecture in which helix VI is short and tightly packed, and is distinct from all other GPCR structures reported so far. Within this unique transmembrane fold is an extremely narrow and highly hydrophilic pocket that is not amenable to the binding of traditional GPCR ligands. We show that such a pocket is conserved across all FZDs, which may explain the long-standing difficulties in the development of ligands for these receptors. Molecular dynamics simulations on the microsecond timescale and mutational analysis uncovered two coupled, dynamic kinks located at helix VII that are involved in FZD4 activation. The stability of the structure in its ligand-free form, an unfavourable pocket for ligand binding and the two unusual kinks on helix VII suggest that FZDs may have evolved a novel ligand-recognition and activation mechanism that is distinct from that of other GPCRs. The crystal structure of the Frizzled 4 receptor transmembrane domain is reported to a resolution of 2.4 Å in a ligand-free state. [ABSTRACT FROM AUTHOR]

The crystal structure of the rhodopsin-arrestin complex provides important insights into how G protein-coupled receptor signaling is terminated by arrestin and a structural basis for understanding the mechanism of arrestin-based signaling. [ABSTRACT FROM AUTHOR]

G-protein-coupled receptors (GPCRs) signal primarily through G proteins or arrestins. Arrestin binding to GPCRs blocks G protein interaction and redirects signalling to numerous G-protein-independent 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 transmembrane helix 7 and helix 8, to recruit arrestin. Correspondingly, arrestin adopts the pre-activated conformation, with a ∼20° rotation between the amino and carboxy domains, which opens up a cleft in arrestin to accommodate a short helix formed by the second intracellular loop of rhodopsin. This structure provides a basis for understanding GPCR-mediated arrestin-biased signalling and demonstrates the power of X-ray lasers for advancing the frontiers of structural biology. [ABSTRACT FROM AUTHOR]

The evolution of glucocorticoid drugs was driven by the demand of lowering the unwanted side effects, while keeping the beneficial anti-inflammatory effects. Potency is an important aspect of this evolution as many undesirable side effects are associated with use of high-dose glucocorticoids. The side effects can be minimized by highly potent glucocorticoids that achieve the same treatment effects at lower doses. This demand propelled the continuous development of synthetic glucocorticoids with increased potencies, but the structural basis of their potencies is poorly understood. To determine the mechanisms underlying potency, we solved the X-ray structures of the glucocorticoid receptor (GR) ligand-binding domain (LBD) bound to its endogenous ligand, cortisol, which has relatively low potency, and a highly potent synthetic glucocorticoid, mometasone furoate (MF). The cortisol-bound GR LBD revealed that the flexibility of the C1-C2 single bond in the steroid A ring is primarily responsible for the low affinity of cortisol to GR. In contrast, we demonstrate that the very high potency of MF is achieved by its C-17α furoate group completely filling the ligand-binding pocket, thus providing additional anchor contacts for high-affinity binding. A single amino acid in the ligand-binding pocket, Q642, plays a discriminating role in ligand potency between MF and cortisol. Structure-based design led to synthesis of several novel glucocorticoids with much improved potency and efficacy. Together, these results reveal key structural mechanisms of glucocorticoid potency and provide a rational basis for developing novel highly potent glucocorticoids. [ABSTRACT FROM AUTHOR]

Strigolactones (SLs) are a group of newly identified plant hormones that control plant shoot branching. SL signalling requires the hormone-dependent interaction of DWARF 14 (D14), a probable candidate SL receptor, with DWARF 3 (D3), an F-box component of the Skp-Cullin-F-box (SCF) E3 ubiquitin ligase complex. Here we report the characterization of a dominant SL-insensitive rice (Oryza sativa) mutant dwarf 53 (d53) and the cloning of D53, which encodes a substrate of the SCFD3 ubiquitination complex and functions as a repressor of SL signalling. Treatments with GR24, a synthetic SL analogue, cause D53 degradation via the proteasome in a manner that requires D14 and the SCFD3 ubiquitin ligase, whereas the dominant form of D53 is resistant to SL-mediated degradation. Moreover, D53 can interact with transcriptional co-repressors known as TOPLESS-RELATED PROTEINS. Our results suggest a model of SL signalling that involves SL-dependent degradation of the D53 repressor mediated by the D14-D3 complex. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "Crystal structures of two phytohormone signal-transducing α/β hydrolases: karrikin-signaling KAI2 and strigolactone-signaling DWARF14" in the February 5, 2013 issue.

Background Expression of the polymeric immunoglobulin receptor (pIgR), a transporter of polymeric IgA and IgM, is commonly increased in response to viral or bacterial infections, linking innate and adaptive immunity. Abnormal expression of pIgR in cancer was also observed, but its clinical relevance remains uncertain. Methods A human hepatocellular carcinoma (HCC) tissue microarray (n = 254) was used to investigate the association between pIgR expression and early recurrence. An experimental lung metastasis model using severe combined immune-deficient mice was applied to determine the metastatic potential of Madin–Darby canine kidney (n = 5 mice per group) and SMMC-7721 (n = 12 mice per group) cells overexpressing pIgR vs control cells. RNA interference, immunoprecipitation, and immunoblotting were performed to investigate the potential role for pIgR in the induction of epithelial–mesenchymal transition (EMT). In vitro studies (co-immunoprecipitation, immunoblotting, and migration, invasion, and adhesion assays) were used to determine the mechanisms behind pIgR-mediated metastasis. All statistical tests were two-sided. Results High expression of pIgR was statistically significantly associated with early recurrence in early-stage HCC and in hepatitis B surface antigen–positive HCC patients (log-rank P = .02). Mice injected with pIgR-overexpressing cells had a statistically significantly higher number of lung metastases compared with respective control cells (Madin–Darby canine kidney cells: pIgR mean = 29.4 metastatic nodules per lung vs control mean = 0.0 metastatic nodules per lung, difference = 29.4 metastatic nodules per lung, 95% confidence interval = 13.0 to 45.8, P = .001; SMMC-7721 cells: pIgR mean = 10.4 metastatic nodules per lung vs control mean = 2.2 metastatic nodules per lung, difference = 8.2 metastatic nodules per lung, 95% confidence interval = 1.0 to 15.5, P = .03). Furthermore, high expression of pIgR was sufficient to induce EMT through activation of Smad signaling. Conclusions pIgR plays a role in the induction of EMT. Our results identify pIgR as a potential link between hepatitis B virus–derived hepatitis and HCC metastasis and provide evidence in support of pIgR as a prognostic biomarker for HCC and a potential therapeutic target. [ABSTRACT FROM PUBLISHER]

Presents information on a study which discussed the use of colony color assay with the 5-fluoroorotic acid negative selection for analyzing RNA-protein interactions in vivo. Information on the yeast three-hybrid system; Development of the color assay; Materials and methods; Results and discussion.

A correction to the article "DWARF 53 acts as a repressor of strigolactone signalling in rice" that was published in the 2013 issue is presented.