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Annual Review of Biochemistry Jun 2018G protein-coupled receptors (GPCRs) mediate the majority of cellular responses to external stimuli. Upon activation by a ligand, the receptor binds to a partner... (Review)
Review
G protein-coupled receptors (GPCRs) mediate the majority of cellular responses to external stimuli. Upon activation by a ligand, the receptor binds to a partner heterotrimeric G protein and promotes exchange of GTP for GDP, leading to dissociation of the G protein into α and βγ subunits that mediate downstream signals. GPCRs can also activate distinct signaling pathways through arrestins. Active states of GPCRs form by small rearrangements of the ligand-binding, or orthosteric, site that are amplified into larger conformational changes. Molecular understanding of the allosteric coupling between ligand binding and G protein or arrestin interaction is emerging from structures of several GPCRs crystallized in inactive and active states, spectroscopic data, and computer simulations. The coupling is loose, rather than concerted, and agonist binding does not fully stabilize the receptor in an active conformation. Distinct intermediates whose populations are shifted by ligands of different efficacies underlie the complex pharmacology of GPCRs.
Topics: Allosteric Regulation; Binding Sites; Conserved Sequence; Crystallography, X-Ray; Energy Metabolism; Humans; Ligands; Models, Molecular; Protein Conformation; Receptors, G-Protein-Coupled
PubMed: 29925258
DOI: 10.1146/annurev-biochem-060614-033910 -
Nature Structural & Molecular Biology Jan 2018G-protein-coupled receptors (GPCRs) relay numerous extracellular signals by triggering intracellular signaling through coupling with G proteins and arrestins. Recent... (Review)
Review
G-protein-coupled receptors (GPCRs) relay numerous extracellular signals by triggering intracellular signaling through coupling with G proteins and arrestins. Recent breakthroughs in the structural determination of GPCRs and GPCR-transducer complexes represent important steps toward deciphering GPCR signal transduction at a molecular level. A full understanding of the molecular basis of GPCR-mediated signaling requires elucidation of the dynamics of receptors and their transducer complexes as well as their energy landscapes and conformational transition rates. Here, we summarize current insights into the structural plasticity of GPCR-G-protein and GPCR-arrestin complexes that underlies the regulation of the receptor's intracellular signaling profile.
Topics: Allosteric Site; Animals; Electron Spin Resonance Spectroscopy; GTP-Binding Proteins; Humans; Ligands; Protein Binding; Protein Domains; Protein Structure, Secondary; Receptors, G-Protein-Coupled; Signal Transduction; beta-Arrestins
PubMed: 29323277
DOI: 10.1038/s41594-017-0011-7 -
Biochemical Society Transactions Nov 2021The glucocorticoid receptor (GR) is a steroid hormone-activated transcription factor that binds to various glucocorticoid response elements to up- or down- regulate the... (Review)
Review
The glucocorticoid receptor (GR) is a steroid hormone-activated transcription factor that binds to various glucocorticoid response elements to up- or down- regulate the transcription of thousands of genes involved in metabolism, development, stress and inflammatory responses. GR consists of two domains enabling interaction with glucocorticoids, DNA response elements and coregulators, as well as a large intrinsically disordered region that mediates condensate formation. A growing body of structural studies during the past decade have shed new light on GR interactions, providing a new understanding of the mechanisms driving context-specific GR activity. Here, we summarize the established and emerging mechanisms of action of GR, primarily from a structural perspective. This minireview also discusses how the current state of knowledge of GR function may guide future glucocorticoid design with an improved therapeutic index for different inflammatory disorders.
Topics: Animals; DNA; Glucocorticoids; Humans; Protein Binding; Protein Conformation; RNA; Receptors, Glucocorticoid
PubMed: 34709368
DOI: 10.1042/BST20210419 -
Nature Aug 2023Arrestins have pivotal roles in regulating G protein-coupled receptor (GPCR) signalling by desensitizing G protein activation and mediating receptor internalization. It...
Arrestins have pivotal roles in regulating G protein-coupled receptor (GPCR) signalling by desensitizing G protein activation and mediating receptor internalization. It has been proposed that the arrestin binds to the receptor in two different conformations, 'tail' and 'core', which were suggested to govern distinct processes of receptor signalling and trafficking. However, little structural information is available for the tail engagement of the arrestins. Here we report two structures of the glucagon receptor (GCGR) bound to β-arrestin 1 (βarr1) in glucagon-bound and ligand-free states. These structures reveal a receptor tail-engaged binding mode of βarr1 with many unique features, to our knowledge, not previously observed. Helix VIII, instead of the receptor core, has a major role in accommodating βarr1 by forming extensive interactions with the central crest of βarr1. The tail-binding pose is further defined by a close proximity between the βarr1 C-edge and the receptor helical bundle, and stabilized by a phosphoinositide derivative that bridges βarr1 with helices I and VIII of GCGR. Lacking any contact with the arrestin, the receptor core is in an inactive state and loosely binds to glucagon. Further functional studies suggest that the tail conformation of GCGR-βarr governs βarr recruitment at the plasma membrane and endocytosis of GCGR, and provides a molecular basis for the receptor forming a super-complex simultaneously with G protein and βarr to promote sustained signalling within endosomes. These findings extend our knowledge about the arrestin-mediated modulation of GPCR functionalities.
Topics: beta-Arrestin 1; Cell Membrane; Endocytosis; Endosomes; Glucagon; Heterotrimeric GTP-Binding Proteins; Ligands; Phosphatidylinositols; Receptors, Glucagon; Protein Binding
PubMed: 37558880
DOI: 10.1038/s41586-023-06420-x -
Nature Jun 2023G protein-coupled receptors (GPCRs) generally accommodate specific ligands in the orthosteric-binding pockets. Ligand binding triggers a receptor allosteric...
G protein-coupled receptors (GPCRs) generally accommodate specific ligands in the orthosteric-binding pockets. Ligand binding triggers a receptor allosteric conformational change that leads to the activation of intracellular transducers, G proteins and β-arrestins. Because these signals often induce adverse effects, the selective activation mechanism for each transducer must be elucidated. Thus, many orthosteric-biased agonists have been developed, and intracellular-biased agonists have recently attracted broad interest. These agonists bind within the receptor intracellular cavity and preferentially tune the specific signalling pathway over other signalling pathways, without allosteric rearrangement of the receptor from the extracellular side. However, only antagonist-bound structures are currently available, and there is no evidence to support that biased agonist binding occurs within the intracellular cavity. This limits the comprehension of intracellular-biased agonism and potential drug development. Here we report the cryogenic electron microscopy structure of a complex of G and the human parathyroid hormone type 1 receptor (PTH1R) bound to a PTH1R agonist, PCO371. PCO371 binds within an intracellular pocket of PTH1R and directly interacts with G. The PCO371-binding mode rearranges the intracellular region towards the active conformation without extracellularly induced allosteric signal propagation. PCO371 stabilizes the significantly outward-bent conformation of transmembrane helix 6, which facilitates binding to G proteins rather than β-arrestins. Furthermore, PCO371 binds within the highly conserved intracellular pocket, activating 7 out of the 15 class B1 GPCRs. Our study identifies a new and conserved intracellular agonist-binding pocket and provides evidence of a biased signalling mechanism that targets the receptor-transducer interface.
Topics: Humans; Allosteric Regulation; beta-Arrestins; Binding Sites; Cryoelectron Microscopy; Drug Development; GTP-Binding Protein alpha Subunits, Gs; Imidazolidines; Ligands; Models, Molecular; Protein Conformation; Receptors, G-Protein-Coupled; Signal Transduction
PubMed: 37286611
DOI: 10.1038/s41586-023-06169-3 -
Nature Sep 2021Olfactory systems must detect and discriminate amongst an enormous variety of odorants. To contend with this challenge, diverse species have converged on a common...
Olfactory systems must detect and discriminate amongst an enormous variety of odorants. To contend with this challenge, diverse species have converged on a common strategy in which odorant identity is encoded through the combinatorial activation of large families of olfactory receptors, thus allowing a finite number of receptors to detect a vast chemical world. Here we offer structural and mechanistic insight into how an individual olfactory receptor can flexibly recognize diverse odorants. We show that the olfactory receptor MhOR5 from the jumping bristletail Machilis hrabei assembles as a homotetrameric odorant-gated ion channel with broad chemical tuning. Using cryo-electron microscopy, we elucidated the structure of MhOR5 in multiple gating states, alone and in complex with two of its agonists-the odorant eugenol and the insect repellent DEET. Both ligands are recognized through distributed hydrophobic interactions within the same geometrically simple binding pocket located in the transmembrane region of each subunit, suggesting a structural logic for the promiscuous chemical sensitivity of this receptor. Mutation of individual residues lining the binding pocket predictably altered the sensitivity of MhOR5 to eugenol and DEET and broadly reconfigured the receptor's tuning. Together, our data support a model in which diverse odorants share the same structural determinants for binding, shedding light on the molecular recognition mechanisms that ultimately endow the olfactory system with its immense discriminatory capacity.
Topics: Animals; Binding Sites; Cell Line; DEET; Eugenol; Insect Proteins; Insecta; Ion Channel Gating; Ion Channels; Models, Molecular; Mutation; Odorants; Protein Binding; Protein Structure, Quaternary; Receptors, Odorant; Substrate Specificity
PubMed: 34349260
DOI: 10.1038/s41586-021-03794-8 -
Cell May 2023Semliki Forest virus (SFV) is an alphavirus that uses the very-low-density lipoprotein receptor (VLDLR) as a receptor during infection of its vertebrate hosts and...
Semliki Forest virus (SFV) is an alphavirus that uses the very-low-density lipoprotein receptor (VLDLR) as a receptor during infection of its vertebrate hosts and insect vectors. Herein, we used cryoelectron microscopy to study the structure of SFV in complex with VLDLR. We found that VLDLR binds multiple E1-DIII sites of SFV through its membrane-distal LDLR class A (LA) repeats. Among the LA repeats of the VLDLR, LA3 has the best binding affinity to SFV. The high-resolution structure shows that LA3 binds SFV E1-DIII through a small surface area of 378 Å, with the main interactions at the interface involving salt bridges. Compared with the binding of single LA3s, consecutive LA repeats around LA3 promote synergistic binding to SFV, during which the LAs undergo a rotation, allowing simultaneous key interactions at multiple E1-DIII sites on the virion and enabling the binding of VLDLRs from divergent host species to SFV.
Topics: Alphavirus; Cryoelectron Microscopy; Semliki forest virus; Receptors, LDL; Receptors, Virus
PubMed: 37098345
DOI: 10.1016/j.cell.2023.03.032 -
Nature Feb 2016Adeno-associated virus (AAV) vectors are currently the leading candidates for virus-based gene therapies because of their broad tissue tropism, non-pathogenic nature and...
Adeno-associated virus (AAV) vectors are currently the leading candidates for virus-based gene therapies because of their broad tissue tropism, non-pathogenic nature and low immunogenicity. They have been successfully used in clinical trials to treat hereditary diseases such as haemophilia B (ref. 2), and have been approved for treatment of lipoprotein lipase deficiency in Europe. Considerable efforts have been made to engineer AAV variants with novel and biomedically valuable cell tropisms to allow efficacious systemic administration, yet basic aspects of AAV cellular entry are still poorly understood. In particular, the protein receptor(s) required for AAV entry after cell attachment remains unknown. Here we use an unbiased genetic screen to identify proteins essential for AAV serotype 2 (AAV2) infection in a haploid human cell line. The most significantly enriched gene of the screen encodes a previously uncharacterized type I transmembrane protein, KIAA0319L (denoted hereafter as AAV receptor (AAVR)). We characterize AAVR as a protein capable of rapid endocytosis from the plasma membrane and trafficking to the trans-Golgi network. We show that AAVR directly binds to AAV2 particles, and that anti-AAVR antibodies efficiently block AAV2 infection. Moreover, genetic ablation of AAVR renders a wide range of mammalian cell types highly resistant to AAV2 infection. Notably, AAVR serves as a critical host factor for all tested AAV serotypes. The importance of AAVR for in vivo gene delivery is further highlighted by the robust resistance of Aavr(-/-) (also known as Au040320(-/-) and Kiaa0319l(-/-)) mice to AAV infection. Collectively, our data indicate that AAVR is a universal receptor involved in AAV infection.
Topics: Animals; Antibodies; Cell Line; Dependovirus; Endocytosis; Female; Gene Deletion; Genetic Therapy; Host Specificity; Humans; Male; Mice; Parvoviridae Infections; Receptors, Cell Surface; Receptors, Virus; Viral Tropism; Virus Internalization; trans-Golgi Network
PubMed: 26814968
DOI: 10.1038/nature16465 -
Science Advances May 2023Kaposi's sarcoma-associated herpesvirus (KSHV) has been implicated in the pathogenesis of Kaposi's sarcoma (KS) and other malignancies. The cellular origin of KS has...
Kaposi's sarcoma-associated herpesvirus (KSHV) has been implicated in the pathogenesis of Kaposi's sarcoma (KS) and other malignancies. The cellular origin of KS has been suggested to be either mesenchymal stem cells (MSCs) or endothelial cells. However, receptor(s) for KSHV to infect MSCs remains unknown. By combining bioinformatics analysis and shRNA screening, we identify neuropilin 1 (NRP1) as an entry receptor for KSHV infection of MSCs. Functionally, NRP1 knockout and overexpression in MSCs significantly reduce and promote, respectively, KSHV infection. Mechanistically, NRP1 facilitated the binding and internalization of KSHV by interacting with KSHV glycoprotein B (gB), which was blocked by soluble NRP1 protein. Furthermore, NRP1 interacts with TGF-β receptor type 2 (TGFBR2) through their respective cytoplasmic domains and thus activates the TGFBR1/2 complex, which facilitates the macropinocytosis-mediated KSHV internalization via the small GTPases Cdc42 and Rac1. Together, these findings implicate that KSHV has evolved a strategy to invade MSCs by harnessing NRP1 and TGF-beta receptors to stimulate macropinocytosis.
Topics: Receptor, Transforming Growth Factor-beta Type I; Neuropilin-1; Herpesvirus 8, Human; Endothelial Cells; Mesenchymal Stem Cells
PubMed: 37224259
DOI: 10.1126/sciadv.adg1778