Adhesion GPCR Latrophilin 3 regulates synaptic function of cone photoreceptors in a trans-synaptic manner.

Cone photoreceptors mediate daylight vision in vertebrates. Changes in neurotransmitter release at cone synapses encode visual information and is subject to precise control by negative feedback from enigmatic horizontal cells. However, the mechanisms that orchestrate this modulation are poorly understood due to a virtually unknown landscape of molecular players. Here, we report a molecular player operating selectively at cone synapses that modulates effects of horizontal cells on synaptic release. Using an unbiased proteomic screen, we identified an adhesion GPCR Latrophilin3 (LPHN3) in horizontal cell dendrites that engages in transsynaptic control of cones. We detected and characterized a prominent splice isoform of LPHN3 that excludes a element with inhibitory influence on transsynaptic interactions. A gain-of-function mouse model specifically routing LPHN3 splicing to this isoform but not knockout of LPHN3 diminished CaV1.4 calcium channel activity profoundly disrupted synaptic release by cones and resulted in synaptic transmission deficits. These findings offer molecular insight into horizontal cell modulation on cone synaptic function and more broadly demonstrate the importance of alternative splicing in adhesion GPCRs for their physiological function.

Spontaneous Pneumothorax in Patients of COVID 19 Pneumonia.

COVID 19 pandemic has put a massive strain on healthcare all over the world. Every day new data is getting released and various complications are being reported in patients of COVID 19 Pneumonia. One such complication is pneumothorax and pneumomediastinum. Both these conditions can lead to an increase in mortality and morbidity in patients with COVID 19 pneumonia. We studied 476 patients of COVID 19 pneumonia at our hospital, out of which 18 (3.78%) had developed pneumothorax and/or pneumomediastinum. While most of these patients were on some form of positive pressure ventilation (invasive/non-invasive), some of them had a HRCT Chest suggestive of either air trapping and/or cyst formation. Three patients had developed bilateral pneumothorax while on non-invasive ventilator. Nine of the 18 patients expired and nine were discharged.Through this article, we would like to emphasize that an acute deterioration in hypoxemia in a COVID-19 patient could indicate a pneumothorax. Pneumothorax as well as pulmonary thromboembolism are reported complications in COVID-19 and clinician vigilance is required during assessment of patients, as both share the common symptom of breathlessness and therefore can mimic each other.

Synaptic adhesion protein ELFN1 is a selective allosteric modulator of group III metabotropic glutamate receptors in trans.

Functional characterization of the GPCR interactome has been focused predominantly on intracellular interactions, yet GPCRs are increasingly found in complex with extracellular proteins. Extracellular leucine-rich repeat fibronectin type III domain containing 1 (ELFN1) was recently reported to physically anchor mGluR6 and mGluR7 across retinal and hippocampal synapses, respectively; however, the consequence of transsynaptic interactions on properties and pharmacology of these receptors are unknown. In the current study, we explore the effects of ELFN1 on mGluR signaling and pharmacology. First, we established the binding specificity of ELFN1 and found it to be recruited selectively to all group III mGluRs (mGluR4, mGluR6, mGluR7, and mGluR8), but not other mGluR species. Using site-directed mutagenesis we mapped binding determinants of this interaction to two distinct sites on the ELFN1 ectodomain. To evaluate functional aspects of the interaction, we developed a transcellular signaling assay in reconstituted HEK293 cells which monitors changes in mGluR activity in one cell following its exposure to separate ELFN1-containing cells. Using this platform, we found that ELFN1 acts as an allosteric modulator of class III mGluR activity in suppressing cAMP accumulation: altering both agonist-induced and constitutive receptor activity. Using bioluminescence resonance energy transfer-based real-time kinetic assays, we established that ELFN1 alters the ability of mGluRs to activate G proteins. Our findings demonstrate that core properties of class III mGluRs can be altered via extracellular interactions with ELFN1 which serves as a transsynaptic allosteric modulator for these receptors. Furthermore, our unique assay platform opens avenues for exploring transcellular/transsynaptic pharmacology of other GPCR transcomplexes.

Novel GNB1 mutations disrupt assembly and function of G protein heterotrimers and cause global developmental delay in humans.

Global developmental delay (GDD), often accompanied by intellectual disability, seizures and other features is a severe, clinically and genetically highly heterogeneous childhood-onset disorder. In cases where genetic causes have been identified, de novo mutations in neuronally expressed genes are a common scenario. These mutations can be best identified by exome sequencing of parent-offspring trios. De novo mutations in the guanine nucleotide-binding protein, beta 1 (GNB1) gene, encoding the Gß1 subunit of heterotrimeric G proteins, have recently been identified as a novel genetic cause of GDD. Using exome sequencing, we identified 14 different novel variants (2 splice site, 2 frameshift and 10 missense changes) in GNB1 in 16 pediatric patients. One mutation (R96L) was recurrently found in three ethnically diverse families with an autosomal dominant mode of inheritance. Ten variants occurred de novo in the patients. Missense changes were functionally tested for their pathogenicity by assaying the impact on complex formation with Gγ and resultant mutant Gßγ with Gα. Signaling properties of G protein complexes carrying mutant Gß1 subunits were further analyzed by their ability to couple to dopamine D1R receptors by real-time bioluminescence resonance energy transfer (BRET) assays. These studies revealed altered functionality of the missense mutations R52G, G64V, A92T, P94S, P96L, A106T and D118G but not for L30F, H91R and K337Q. In conclusion, we demonstrate a pathogenic role of de novo and autosomal dominant mutations in GNB1 as a cause of GDD and provide insights how perturbation in heterotrimeric G protein function contributes to the disease.

Iodine(III)-Mediated, Controlled Di- or Monoiodination of Phenols.

An oxidative procedure for the electrophilic iodination of phenols was developed by using iodosylbenzene as a nontoxic iodine(III)-based oxidant and ammonium iodide as a cheap iodine atom source. A totally controlled monoiodination was achieved by buffering the reaction medium with K3PO4. This protocol proceeds with short reaction times, at mild temperatures, in an open flask, and generally with high yields. Gram-scale reactions, as well as the scope of this protocol, were explored with electron-rich and electron-poor phenols as well as heterocycles. Quantum chemistry calculations revealed PhII(OH)·NH3 to be the most plausible iodinating active species as a reactive "I+" synthon. In light of the relevance of the iodoarene moiety, we present herein a practical, efficient, and simple procedure with a broad functional group scope that allows access to the iodoarene core unit.

ß-Cyclodextrin: A Green and Efficient Supramolecular Catalyst for Organic Transformations.

ß-Cyclodextrin is cyclic oligosaccharide possessing hydrophobic cavity, which binds the substrates selectively and catalyze number of organic transformations with high selectivity. It catalyzes the reaction by non-covalent supramolecular bonding with reversible formation of host-guest complexes as seen in enzymes. This account summarizes our efforts in designing a good number of important organic transformations using ß-cyclodextrin and its derivatives. These reactions were performed in neat, aqueous as well as organic media. Greener synthetic routes to a variety of biologically relevant organic molecules has been developed. The temperature, solvent and catalyst amount plays in important role in these reactions. ß-Cyclodextrin activates variety of organic compounds like aldehydes, ketones, anhydride, oximes, amines, nitriles and increases the rate of reactions.

Hydroxyurea-Lactose Interaction Study: In Silico and In Vitro Evaluation.

The Maillard reaction between hydroxyurea (a primary amine-containing drug) and lactose (used as an excipient) was explored. The adduct of these compounds was synthesized by heating hydroxyurea with lactose monohydrate at 60 °C in borate buffer (pH 9.2) for 12 h. Synthesis of the adduct was confirmed using UV-visible spectroscopy and Fourier transform infrared, differential scanning calorimetry, high-pressure liquid chromatography, and liquid chromatography-mass spectrometry studies. An in silico investigation of how the adduct formation affected the interactions of hydroxyurea with its biological target oxyhemoglobin, to which it binds to generate nitric oxide and regulates fetal hemoglobin synthesis, was carried out. The in silico evaluations were complemented by an in vitro assay of the anti-sickling activity. Co-incubation of hydroxyurea with deoxygenated blood samples reduced the percentage of sickled cells from 38% to 12 ± 1.6%, whereas the percentage of sickled cells in samples treated with the adduct was 17 ± 1.2%. This indicated loss of anti-sickling activity in the case of the adduct. This study confirmed that hydroxyurea can participate in a Maillard reaction if lactose is used as a diluent. Although an extended study at environmentally feasible temperatures was not carried out in the present investigation, the partial loss of the anti-sickling activity of hydroxyurea was investigated along with the in silico drug-target interactions. The results indicated that the use of lactose in hydroxyurea formulations needs urgent reconsideration and that lactose must be replaced by other diluents that do not form Maillard adducts.

Standardization of homeopathic mother tincture of Toxicodendron pubescens and correlation of its flavonoid markers with the biological activity.

BACKGROUND: Standardization and quality control of homeopathic drugs is very challenging. As mother tinctures are derived from complex natural resources, there is a need of systematic evaluation of chemical markers which correlate with the proposed biological activities of mother tinctures. METHODS: In present study, High-Performance Thin-Layer Chromatography (HPTLC) standardization method of homeopathic mother tinctures of Toxicodendron pubescens using quercitrin and rutin as chemical markers is validated and correlations of content of these markers with its anti-inflammatory effects are established. For HPTLC analysis, precoated silica gel plates were used as stationary phase. Two flavonoids, namely quercitrin and rutin were used as markers. Separation was achieved using methylene chloride:methanol:water:glacial acetic acid (15:1.5:1:8 v/v/v) as mobile phase. The developed plates were scanned at 365 nm. RESULTS: It was observed that quercitrin (Rf value 0.63) and Rutin (Rf value 0.41) are well resolved. The minimum detectable concentrations for quercitrin and rutin were 5 ng/spot. The linearity range was between 100 and 2000 ng/spot for both the markers. Subsequently, anti-inflammatory activity of these formulations was determined against carrageenan-induced paw edema in rats, pain threshold determined by electronic Von-Frey apparatus and paw withdrawal latency (PWL) on hot-plate. All the tested formulations of Rhus Tox showed anti-inflammatory and analgesic activity against carrageenan induced paw edema in rats. Quantitative correlation between the content of markers and anti-inflammatory activity of mother tinctures was established. RESULTS: Anti-inflammatory effect as well as effect on paw withdrawal and pain threshold, at third hour after carrageenan injection, correlated with quercitrin and rutin content in the respective formulations. CONCLUSIONS: This study validates a quantitative HPTLC method for standardization of homeopathic mother tincture of Rhus Tox and establishes quercitrin and rutin as markers corresponding its biological activity. Contents of quercitrin and rutin in T. pubescens mother tincture correlates with its anti-inflammatory and analgesic actions and the validated HPTLC method can be used in standardization of homeopathic mother tincture of T. pubescens.

Structural and functional evolution of chitinase-like proteins from plants.

The plant genome contains a large number of sequences that encode catalytically inactive chitinases referred to as chitinase-like proteins (CLPs). Although CLPs share high sequence and structural homology with chitinases of glycosyl hydrolase 18 (TIM barrel domain) and 19 families, they may lack the binding/catalytic activity. Molecular genetic analysis revealed that gene duplication events followed by mutation in the existing chitinase gene have resulted in the loss of activity. The evidences show that adaptive functional diversification of the CLPs has been achieved through alterations in the flexible regions than in the rigid structural elements. The CLPs plays an important role in the defense response against pathogenic attack, biotic and abiotic stress. They are also involved in the growth and developmental processes of plants. Since the physiological roles of CLPs are similar to chitinase, such mutations have led to plurifunctional enzymes. The biochemical and structural characterization of the CLPs is essential for understanding their roles and to develop potential utility in biotechnological industries. This review sheds light on the structure-function evolution of CLPs from chitinases.

Lipid-directed vinculin dimerization.

Vinculin localizes to cellular adhesions where it regulates motility, migration, development, wound healing, and response to force. Importantly, vinculin loss results in cancer phenotypes, cardiovascular disease, and embryonic lethality. At the plasma cell membrane, the most abundant phosphoinositide, phosphatidylinositol 4,5-bisphosphate (PIP2), binds the vinculin tail domain, Vt, and triggers homotypic and heterotypic interactions that amplify binding of vinculin to the actin network. Binding of PIP2 to Vt is necessary for maintaining optimal focal adhesions, for organizing stress fibers, for cell migration and spreading, and for the control of vinculin dynamics and turnover of focal adhesions. While the recently determined Vt/PIP2 crystal structure revealed the conformational changes occurring upon lipid binding and oligomerization, characterization of PIP2-induced vinculin oligomerization has been challenging in the adhesion biology field. Here, via a series of novel biochemical assays not performed in previous studies that relied on chemical cross-linking, we characterize the PIP2-induced vinculin oligomerization. Our results show that Vt/PIP2 forms a tight dimer with Vt or with the muscle-specific vinculin isoform, metavinculin, at sites of adhesion at the cell membrane. Insight into how PIP2 regulates clustering and into mechanisms that regulate cell adhesion allows the development for a more definite sensor for PIP2, and our developed techniques can be applied generally and thus open the door for the characterization of many other protein/PIP2 complexes under physiological conditions.

Ligand-bound structures of 3-deoxy-D-manno-octulosonate 8-phosphate phosphatase from Moraxella catarrhalis reveal a water channel connecting to the active site for the second step of catalysis.

KdsC, the third enzyme of the 3-deoxy-D-manno-octulosonic acid (KDO) biosynthetic pathway, catalyzes a substrate-specific reaction to hydrolyze 3-deoxy-D-manno-octulosonate 8-phosphate to generate a molecule of KDO and phosphate. KdsC is a phosphatase that belongs to the C0 subfamily of the HAD superfamily. To understand the molecular basis for the substrate specificity of this tetrameric enzyme, the crystal structures of KdsC from Moraxella catarrhalis (Mc-KdsC) with several combinations of ligands, namely metal ion, citrate and products, were determined. Various transition states of the enzyme have been captured in these crystal forms. The ligand-free and ligand-bound crystal forms reveal that the binding of ligands does not cause any specific conformational changes in the active site. However, the electron-density maps clearly showed that the conformation of KDO as a substrate is different from the conformation adopted by KDO when it binds as a cleaved product. Furthermore, structural evidence for the existence of an intersubunit tunnel has been reported for the first time in the C0 subfamily of enzymes. A role for this tunnel in transferring water molecules from the interior of the tetrameric structure to the active-site cleft has been proposed. At the active site, water molecules are required for the formation of a water bridge that participates as a proton shuttle during the second step of the two-step phosphoryl-transfer reaction. In addition, as the KDO biosynthesis pathway is a potential antibacterial target, pharmacophore-based virtual screening was employed to identify inhibitor molecules for the Mc-KdsC enzyme.

An efficient synthesis of 3-indolyl-3-hydroxy oxindoles and 3,3-di(indolyl)indolin-2-ones catalyzed by sulfonated ß-CD as a supramolecular catalyst in water.

Sulfonated-ß-cyclodextrin (ß-CD-SO3H) promoted efficient and fast electrophilic substitution reaction of indoles with various isatins reflux in water is reported affording various 3-indolyl-3-hydroxy oxindoles and 3,3-di(indolyl)indolin-2-ones in good to excellent yields in short reaction time.

Modification of pharmacological activity of nebivolol due to Maillard reaction.

Lactose is used as an excipient in solid dosage forms of nebivolol. Ultraviolet spectroscopy, Fourier-transform infrared spectroscopy and differential scanning calorimetry were used to study the interaction between nebivolol and lactose. The formation of a Maillard product was noted in aqueous mixtures of nebivolol and lactose heated at 60°C at unbuffered and buffered alkaline pH. A similar Maillard adduct formation was evident within 15 days in a dry physical mixture of nebivolol and lactose maintained at 40°C and 75% relative humidity in the dark. High-performance liquid chromatography and liquid chromatography-mass spectrometry analyses of the reaction mixtures confirmed the formation of a nebivolol-lactose adduct. The effects of intravenously administered nebivolol and the nebivolol-lactose adduct on the blood pressure and heart rate of anesthetized normotensive rats were investigated. The bradycardic effect of the adduct was significantly less than that of nebivolol. The present investigation reveals an incompatibility between nebivolol and lactose, leading to the loss of the pharmacological activity of nebivolol. Hence, the use of lactose as an excipient in dosage forms of nebivolol, a secondary amine, needs reconsideration.

Orphan receptor GPR158 serves as a metabotropic glycine receptor: mGlyR.

Glycine is a major neurotransmitter involved in several fundamental neuronal processes. The identity of the metabotropic receptor mediating slow neuromodulatory effects of glycine is unknown. We identified an orphan G protein-coupled receptor, GPR158, as a metabotropic glycine receptor (mGlyR). Glycine and a related modulator, taurine, directly bind to a Cache domain of GPR158, and this event inhibits the activity of the intracellular signaling complex regulator of G protein signaling 7-G protein ß5 (RGS7-Gß5), which is associated with the receptor. Glycine signals through mGlyR to inhibit production of the second messenger adenosine 3',5'-monophosphate. We further show that glycine, but not taurine, acts through mGlyR to regulate neuronal excitability in cortical neurons. These results identify a major neuromodulatory system involved in mediating metabotropic effects of glycine, with implications for understanding cognition and affective states.

Intrabony defect management with a bone graft (hydroxyapatite and ß-tricalcium phosphate) alone and in combination with a diode laser: A randomized control trial.

Objectives: The current research was conducted to evaluate the use of a diode laser and a bone graft (hydroxyapatite [HA] + ß-tricalcium phosphate [ß-TCP]) in healing of intrabony defects. Materials and Methods: In this split-mouth evaluation, 40 patients with bilateral intrabony defects were treated with, Group I (control) - bone graft alone (HA + ß-TCP) and Group II, (test) - bone graft with a diode laser. The clinical and radiologic parameters of all patients, such as plaque index (PI), probing depth (PD), gingival index (GI), gingival recession (GR), and relative clinical attachment level (RCAL) were recorded at baseline, after 3 months and after 6 months. Results: Reductions in PI, PD, GI, GR, and RCAL were found after 6 months. Furthermore, significant differences were displayed in the intra-group comparison while those of the inter-group evaluation (P > 0.05) were insignificant. Conclusion: In both groups, considerable decrease in intrabony pockets was discovered; however, the inter-group comparison was insignificant in relation to GR and RCAL.

Evaluation of the Characteristics of Nano Hybrid Composite Resin Modified with Graphene after Thermomechanical Loading Cycle.

To evaluate the characteristics of a thermomechanically loaded composite resin enhanced with graphene nanoparticles. A total of 60 specimens were manufactured with Test group TG1 (20), TG2 (20), and control group CG (20). All samples were subjected to surface roughness using a three-dimensional (3D) Optical profilometer and flexural strength. All specimens were subjected to thermomechanical cyclic loading. Microhardness measurement was performed with a microhardness tester. The average microhardness and flexural strength were higher in test groups TG1 and TG2 and lowest in control group CG. There was an improvement in surface roughness, flexural strength, and microhardness in the test group after the addition of graphene nanoparticles compared to the control group. Conclusion: The addition of graphene nanoparticles to composite resin significantly improved flexural strength and microhardness. The physical and chemical properties of the composite showed marked improvement.

Structure of the photoreceptor synaptic assembly of the extracellular matrix protein pikachurin with the orphan receptor GPR179.

Precise synapse formation is essential for normal functioning of the nervous system. Retinal photoreceptors establish selective contacts with bipolar cells, aligning the neurotransmitter release apparatus with postsynaptic signaling cascades. This involves transsynaptic assembly between the dystroglycan-dystrophin complex on the photoreceptor and the orphan receptor GPR179 on the bipolar cell, which is mediated by the extracellular matrix protein pikachurin (also known as EGFLAM). This complex plays a critical role in the synaptic organization of photoreceptors and signal transmission, and mutations affecting its components cause blinding disorders in humans. Here, we investigated the structural organization and molecular mechanisms by which pikachurin orchestrates transsynaptic assembly and solved structures of the human pikachurin domains by x-ray crystallography and of the GPR179-pikachurin complex by single-particle, cryo-electron microscopy. The structures reveal molecular recognition principles of pikachurin by the Cache domains of GPR179 and show how the interaction is involved in the transsynaptic alignment of the signaling machinery. Together, these data provide a structural basis for understanding the synaptic organization of photoreceptors and ocular pathology.

Biochemical studies and ligand-bound structures of biphenyl dehydrogenase from Pandoraea pnomenusa strain B-356 reveal a basis for broad specificity of the enzyme.

Biphenyl dehydrogenase, a member of short-chain dehydrogenase/reductase enzymes, catalyzes the second step of the biphenyl/polychlorinated biphenyls catabolic pathway in bacteria. To understand the molecular basis for the broad substrate specificity of Pandoraea pnomenusa strain B-356 biphenyl dehydrogenase (BphB(B-356)), the crystal structures of the apo-enzyme, the binary complex with NAD(+), and the ternary complexes with NAD(+)-2,3-dihydroxybiphenyl and NAD(+)-4,4'-dihydroxybiphenyl were determined at 2.2-, 2.5-, 2.4-, and 2.1-Å resolutions, respectively. A crystal structure representing an intermediate state of the enzyme was also obtained in which the substrate binding loop was ordered as compared with the apo and binary forms but it was displaced significantly with respect to the ternary structures. These five structures reveal that the substrate binding loop is highly mobile and that its conformation changes during ligand binding, starting from a disorganized loop in the apo state to a well organized loop structure in the ligand-bound form. Conformational changes are induced during ligand binding; forming a well defined cavity to accommodate a wide variety of substrates. This explains the biochemical data that shows BphB(B-356) converts the dihydrodiol metabolites of 3,3'-dichlorobiphenyl, 2,4,4'-trichlorobiphenyl, and 2,6-dichlorobiphenyl to their respective dihydroxy metabolites. For the first time, a combination of structural, biochemical, and molecular docking studies of BphB(B-356) elucidate the unique ability of the enzyme to transform the cis-dihydrodiols of double meta-, para-, and ortho-substituted chlorobiphenyls.

Development and biological evaluation of protective effect of kidney targeted N-acetylated chitosan nanoparticles containing thymoquinone for the treatment of DNA damage in cyclophosphamide-induced haemorrhagic cystitis.

Thymoquinone (TQ), the most prominent constituent of Nigella sativa seeds, essential oil, is reported to possess an organ protective effect via Nrf2 expression and activation of Phase-II antioxidant enzymes. Haemorrhagic cystitis is the sudden onset of haematuria combined with bladder pain and irritable bladder symptoms are the known toxic effects of cyclophosphamide (CYP) chemotherapy. The objective of the present study was to investigate and compare the protective effect of thymoquinone (TQ) and thymoquinone nanoparticles (TQ-NP) in the kidney against CYP-induced haemorrhagic cystitis. Primarily, TQ-NP was fabricated by synthesis of N-acetylated chitosan and nanoparticle preparation by the ionic gelation technique. They were characterized by particle size, polydispersive index (PDI), zeta potential, entrapment efficiency (EE), SEM, and dynamic scattering calorimetry (DSC). Moreover, fluorescein isothiocyanate (FITC) labeled NPs were prepared for biodistribution studies. The protective mechanisms of TQ-NP included its anti-inflammatory activity, inhibitory effects on cytokine levels, and protection against the DNA damage in the bladder epithelium. The cystitis was induced in rats by orally administering 200 mg/kg of CYP. The dose-dependent protective effect of the TQ-NP was determined by intravenously administering 1, 2, and 5 mg/kg of the TQ-NP to CYP-treated rats. The present study revealed that the TQ-NP prepared by ionic gelation method provides kidney targeted delivery of TQ as compared to TQ solution. The mean particle size, PDI, and %EE of TQ-NP were 272.6 nm, 0.216, 70.81 ± 0.12% respectively. The zeta potential of thymoquinone-loaded nanoparticles was found to be -20.7 mV and - 22.6 mV respectively before and after lyophilization. SEM study also confirmed the small size and spherical shape. Pharmacokinetic studies revealed the improvement in half-life and prolonged action of the TQ-NP as compared to the TQ solution. Also, TQ-NP administration showed more protection against the characteristic histological alterations in the bladder in comparison to TQ solution. The present study indicates that TQ-NP exerts potent anti-oxidant, DNA protective and cytokine inhibitory activity at considerably lower concentrations as compared to plain TQ solution. The nano formulation of TQ using N-acetylated chitosan provides effective kidney targeted delivery of TQ, which in turn improves its retention and protective efficacy against CYP-induced haemorrhagic cystitis.

Cryo-EM structure of human GPR158 receptor coupled to the RGS7-Gß5 signaling complex.

GPR158 is an orphan G protein­coupled receptor (GPCR) highly expressed in the brain, where it controls synapse formation and function. GPR158 has also been implicated in depression, carcinogenesis, and cognition. However, the structural organization and signaling mechanisms of GPR158 are largely unknown. We used single-particle cryo­electron microscopy (cryo-EM) to determine the structures of human GPR158 alone and bound to an RGS signaling complex. The structures reveal a homodimeric organization stabilized by a pair of phospholipids and the presence of an extracellular Cache domain, an unusual ligand-binding domain in GPCRs. We further demonstrate the structural basis of GPR158 coupling to RGS7-Gß5. Together, these results provide insights into the unusual biology of orphan receptors and the formation of GPCR-RGS complexes.