During the past few years, crystallography of G protein-coupled receptors (GPCRs) has experienced exponential growth, resulting in the determination of the structures of 16 distinct receptors-9 of ...them in 2012 alone. Including closely related subtype homology models, this coverage amounts to approximately 12% of the human GPCR superfamily. The adrenergic, rhodopsin, and adenosine receptor systems are also described by agonist-bound active-state structures, including a structure of the receptor-G protein complex for the β(2)-adrenergic receptor. Biochemical and biophysical techniques, such as nuclear magnetic resonance and hydrogen-deuterium exchange coupled with mass spectrometry, are providing complementary insights into ligand-dependent dynamic equilibrium between different functional states. Additional details revealed by high-resolution structures illustrate the receptors as allosteric machines that are controlled not only by ligands but also by ions, lipids, cholesterol, and water. This wealth of data is helping redefine our knowledge of how GPCRs recognize such a diverse array of ligands and how they transmit signals 30 angstroms across the cell membrane; it also is shedding light on a structural basis of GPCR allosteric modulation and biased signaling.
G protein-coupled receptors (GPCRs) comprise the most ‘prolific’ family of cell membrane proteins, which share a general mechanism of signal transduction, but greatly vary in ligand recognition and ...function. Crystal structures are now available for rhodopsin, adrenergic, and adenosine receptors in both inactive and activated forms, as well as for chemokine, dopamine, and histamine receptors in inactive conformations. Here we review common structural features, outline the scope of structural diversity of GPCRs at different levels of homology, and briefly discuss the impact of the structures on drug discovery. Given the current set of GPCR crystal structures, a distinct modularity is now being observed between the extracellular (ligand-binding) and intracellular (signaling) regions. The rapidly expanding repertoire of GPCR structures provides a solid framework for experimental and molecular modeling studies, and helps to chart a roadmap for comprehensive structural coverage of the whole superfamily and an understanding of GPCR biological and therapeutic mechanisms.
Cannabinoid receptor 1 (CB1) is the principal target of Δ9-tetrahydrocannabinol (THC), a psychoactive chemical from Cannabis sativa with a wide range of therapeutic applications and a long history of ...recreational use. CB1 is activated by endocannabinoids and is a promising therapeutic target for pain management, inflammation, obesity, and substance abuse disorders. Here, we present the 2.8 Å crystal structure of human CB1 in complex with AM6538, a stabilizing antagonist, synthesized and characterized for this structural study. The structure of the CB1-AM6538 complex reveals key features of the receptor and critical interactions for antagonist binding. In combination with functional studies and molecular modeling, the structure provides insight into the binding mode of naturally occurring CB1 ligands, such as THC, and synthetic cannabinoids. This enhances our understanding of the molecular basis for the physiological functions of CB1 and provides new opportunities for the design of next-generation CB1-targeting pharmaceuticals.
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•AM6538 is presented as a stabilizing, tight binding antagonist of CB1•Crystal structure of human CB1 in complex with AM6538 is determined•Molecular docking predicts CB1 binding modes of THC and synthetic cannabinoids•Resolution of the binding pocket provides path for rational CB1 drug design
A look at ligand engagement with the human CB1 receptor opens up avenues for design of new modulators with favorable physiological profiles.
G protein-coupled receptors (GPCRs), which are modulated by a variety of endogenous and synthetic ligands, represent the largest family of druggable targets in the human genome. Recent structural and ...molecular studies have both transformed and expanded classical concepts of receptor pharmacology and have begun to illuminate the distinct mechanisms by which structurally, chemically, and functionally diverse ligands modulate GPCR function. These molecular insights into ligand engagement and action have enabled new computational methods and accelerated the discovery of novel ligands and tool compounds, especially for understudied and orphan GPCRs. These advances promise to streamline the development of GPCR-targeted medications.
Structural and computational approaches studying GPCR-ligand interactions are shaping fundamental principles in receptor signaling and uncovering new physiological functions for this protein family.
ABSTRACT
The first crystal structure of a G protein‐coupled receptor (GPCR) was that of the bovine rhodopsin, solved in 2000, and is a light receptor within retina rode cells that enables vision by ...transducing a conformational signal from the light‐induced isomerization of retinal covalently bound to the receptor. More than 7 years after this initial discovery and following more than 20 years of technological developments in GPCR expression, stabilization, and crystallography, the high‐resolution structure of the adrenaline binding β2‐adrenergic receptor, a ligand diffusible receptor, was discovered. Since then, high‐resolution structures of more than 53 unique GPCRs have been determined leading to a significant improvement in our understanding of the basic mechanisms of ligand‐binding and ligand‐mediated receptor activation that revolutionized the field of structural molecular pharmacology of GPCRs. Recently, several structures of eight unique lipid‐binding receptors, one of the most difficult GPCR families to study, have been reported. This review presents the outstanding structural and pharmacological features that have emerged from these new lipid receptor structures. The impact of these findings goes beyond mechanistic insights, providing evidence of the fundamental role of GPCRs in the physiological integration of the lipid signaling system, and highlighting the importance of sustained research into the structural biology of GPCRs for the development of new therapeutics targeting lipid receptors.
Molecular determinants regulating the activation of class B G-protein-coupled receptors (GPCRs) by native peptide agonists are largely unknown. We have investigated here the interaction between ...the corticotropin releasing factor receptor type 1 (CRF1R) and its native 40-mer peptide ligand Urocortin-I directly in mammalian cells. By incorporating unnatural amino acid photochemical and new click-chemical probes into the intact receptor expressed in the native membrane of live cells, 44 intermolecular spatial constraints have been derived for the ligand-receptor interaction. The data were analyzed in the context of the recently resolved crystal structure of CRF1R transmembrane domain and existing extracellular domain structures, yielding a complete conformational model for the peptide-receptor complex. Structural features of the receptor-ligand complex yield molecular insights on the mechanism of receptor activation and the basis for discrimination between agonist and antagonist function.
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•Ucn1 binding interface on CRF1R mapped with photochemical probes in cells•Position of Ucn1 in CRF1R determined with a click-chemical probe in cells•Conformational model for ligand-GPCR complex satisfies ∼50 spatial constraints•Insights on class B GPCR activation gained on receptor expressed in native cells
A class B GPCR was systematically engineered to permit crosslinking to its native ligand in cells, and the resultant distance constraints allow modeling agonist binding and receptor activation.
Lipid biology continues to emerge as an area of significant therapeutic interest, particularly as the result of an enhanced understanding of the wealth of signaling molecules with diverse ...physiological properties. This growth in knowledge is epitomized by lysophosphatidic acid (LPA), which functions through interactions with at least six cognate G protein-coupled receptors. Herein, we present three crystal structures of LPA1 in complex with antagonist tool compounds selected and designed through structural and stability analyses. Structural analysis combined with molecular dynamics identified a basis for ligand access to the LPA1 binding pocket from the extracellular space contrasting with the proposed access for the sphingosine 1-phosphate receptor. Characteristics of the LPA1 binding pocket raise the possibility of promiscuous ligand recognition of phosphorylated endocannabinoids. Cell-based assays confirmed this hypothesis, linking the distinct receptor systems through metabolically related ligands with potential functional and therapeutic implications for treatment of disease.
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•LPA1 structure determined with a selective antagonist•Structure-based design led to antagonists with improved characteristics•The LPA1 binding pocket permits extracellular ligand access unlike related S1P1R•Structural analysis predicts metabolic products of cannabinoid ligands bind to LPA1
Structural analyses of a human lysophosphatidic acid receptor reveal plasticity in ligand recognition and suggest mechanisms for modulation of receptors with distinct functions by common ligand scaffolds.
Extending the Structural View of Class B GPCRs de Graaf, Chris; Song, Gaojie; Cao, Can ...
Trends in biochemical sciences (Amsterdam. Regular ed.),
December 2017, 2017-12-00, 20171201, Letnik:
42, Številka:
12
Journal Article
Recenzirano
The secretin-like class B family of G protein-coupled receptors (GPCRs) are key players in hormonal homeostasis. Recent structures of various receptors in complex with a variety of orthosteric and ...allosteric ligands provide fundamental new insights into the function and mechanism of class B GPCRs, including: (i) ligand-induced changes in the relative orientation of the extracellular and transmembrane receptor domains; (ii) intramolecular interaction networks that stabilize conformational changes to accommodate intracellular G protein binding; and (iii) allosteric modulation of receptor activation. This review provides a comprehensive analysis of the structural, biochemical, and pharmacological data on class B GPCRs for understanding ligand–receptor interaction and modulation mechanisms and assessing the potential implications for drug discovery for the secretin-like GPCR family.
Methodological developments in X-ray crystallography and cryo-electron microscopy have enabled the determination of the first full-length and G protein-coupled structures of class B G protein-coupled receptors (GPCRs).
Structural comparison of different class B GPCR–ligand complexes provides insights into the molecular mechanisms of receptor activation, including: (i) ligand-induced conformational changes of extracellular and transmembrane domains; (ii) intramolecular interaction networks facilitating G protein coupling; and (iii) negative and positive allosteric modulation of receptor activation.
The new structures of class B GPCRs reveal novel allosteric binding sites. The structural details of the binding modes of negative and positive allosteric modulators provide new templates for structure-based drug discovery for this pharmaceutically relevant receptor family.
Structural studies of human G protein-coupled receptors (GPCRs) have recently been accelerated through the use of a fusion partner that was inserted into the third intracellular loop. Using chimeras ...of the human β2-adrenergic and human A2A adenosine receptors, we present the methodology and data for the initial selection of an expanded set of fusion partners for crystallizing GPCRs. In particular, use of the thermostabilized apocytochrome b562RIL as a fusion partner displays certain advantages over previously utilized fusion proteins, resulting in a significant improvement in stability and structure of GPCR-fusion constructs.
► A method was developed for the selection of fusion domains for GPCR crystallization ► Apocytochrome b562RIL has advantages over previously utilized T4 lysozyme ► Diffraction quality crystals of two engineered GPCRs were successfully grown ► The method led to the crystal structure of the A2A adenosine receptor at 1.8 Å
The cannabinoid receptor 1 (CB1) is the principal target of the psychoactive constituent of marijuana, the partial agonist Δ9-tetrahydrocannabinol (Δ9-THC). Here we report two agonist-bound crystal ...structures of human CB1 in complex with a tetrahydrocannabinol (AM11542) and a hexahydrocannabinol (AM841) at 2.80 Å and 2.95 Å resolution, respectively. The two CB1-agonist complexes reveal important conformational changes in the overall structure, relative to the antagonist-bound state, including a 53% reduction in the volume of the ligand-binding pocket and an increase in the surface area of the G-protein-binding region. In addition, a 'twin toggle switch' of Phe2003.36 and Trp3566.48 (superscripts denote Ballesteros-Weinstein numbering) is experimentally observed and appears to be essential for receptor activation. The structures reveal important insights into the activation mechanism of CB1 and provide a molecular basis for predicting the binding modes of Δ9-THC, and endogenous and synthetic cannabinoids. The plasticity of the binding pocket of CB1 seems to be a common feature among certain class A G-protein-coupled receptors. These findings should inspire the design of chemically diverse ligands with distinct pharmacological properties.
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