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Carlson AL, Carrazco-Carrillo J, Loder A, Elkhadragy L, Schachtschneider KM, Padilla-Benavides T. The Oncopig as an Emerging Model to Investigate Copper Regulation in Cancer. Int J Mol Sci 2022; 23:14012. [PMID: 36430490 PMCID: PMC9697225 DOI: 10.3390/ijms232214012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Revised: 11/03/2022] [Accepted: 11/10/2022] [Indexed: 11/16/2022] Open
Abstract
Emerging evidence points to several fundamental contributions that copper (Cu) has to promote the development of human pathologies such as cancer. These recent and increasing identification of the roles of Cu in cancer biology highlights a promising field in the development of novel strategies against cancer. Cu and its network of regulatory proteins are involved in many different contextual aspects of cancer from driving cell signaling, modulating cell cycle progression, establishing the epithelial-mesenchymal transition, and promoting tumor growth and metastasis. Human cancer research in general requires refined models to bridge the gap between basic science research and meaningful clinical trials. Classic studies in cultured cancer cell lines and animal models such as mice and rats often present caveats when extended to humans due to inherent genetic and physiological differences. However, larger animal models such as pigs are emerging as more appropriate tools for translational research as they present more similarities with humans in terms of genetics, anatomical structures, organ sizes, and pathological manifestations of diseases like cancer. These similarities make porcine models well-suited for addressing long standing questions in cancer biology as well as in the arena of novel drug and therapeutic development against human cancers. With the emergent roles of Cu in human health and pathology, the pig presents an emerging and valuable model to further investigate the contributions of this metal to human cancers. The Oncopig Cancer Model is a transgenic swine model that recapitulates human cancer through development of site and cell specific tumors. In this review, we briefly outline the relationship between Cu and cancer, and how the novel Oncopig Cancer Model may be used to provide a better understanding of the mechanisms and causal relationships between Cu and molecular targets involved in cancer.
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Affiliation(s)
- Alyssa L. Carlson
- Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, CT 06459, USA
| | - Jaime Carrazco-Carrillo
- Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, CT 06459, USA
| | - Aaron Loder
- Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, CT 06459, USA
| | - Lobna Elkhadragy
- Department of Radiology, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Kyle M. Schachtschneider
- Department of Radiology, University of Illinois at Chicago, Chicago, IL 60607, USA
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, IL 60607, USA
- National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, Urbana, IL 61820, USA
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2
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Tomassi S, Dimmito MP, Cai M, D’Aniello A, Del Bene A, Messere A, Liu Z, Zhu T, Hruby VJ, Stefanucci A, Cosconati S, Mollica A, Di Maro S. CLIPSing Melanotan-II to Discover Multiple Functionally Selective hMCR Agonists. J Med Chem 2022; 65:4007-4017. [DOI: 10.1021/acs.jmedchem.1c01848] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Stefano Tomassi
- Dipartimento di Farmacia, Università degli Studi di Napoli “Federico II”, Via D. Montesano 49, Naples 80131, Italy
| | - Marilisa Pia Dimmito
- Dipartimento di Farmacia, Università di Chieti-Pescara “G. d’Annunzio”, Via dei Vestini 31, Chieti 66100, Italy
| | - Minying Cai
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
| | - Antonia D’Aniello
- DiSTABiF, University of Campania “Luigi Vanvitelli”, Via Vivaldi 43, 81100 Caserta, Italy
| | - Alessandra Del Bene
- DiSTABiF, University of Campania “Luigi Vanvitelli”, Via Vivaldi 43, 81100 Caserta, Italy
| | - Anna Messere
- DiSTABiF, University of Campania “Luigi Vanvitelli”, Via Vivaldi 43, 81100 Caserta, Italy
| | - Zekun Liu
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
| | - Tingyi Zhu
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
| | - Victor J. Hruby
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
| | - Azzurra Stefanucci
- Dipartimento di Farmacia, Università di Chieti-Pescara “G. d’Annunzio”, Via dei Vestini 31, Chieti 66100, Italy
| | - Sandro Cosconati
- DiSTABiF, University of Campania “Luigi Vanvitelli”, Via Vivaldi 43, 81100 Caserta, Italy
| | - Adriano Mollica
- Dipartimento di Farmacia, Università di Chieti-Pescara “G. d’Annunzio”, Via dei Vestini 31, Chieti 66100, Italy
| | - Salvatore Di Maro
- DiSTABiF, University of Campania “Luigi Vanvitelli”, Via Vivaldi 43, 81100 Caserta, Italy
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3
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Structural mechanism of calcium-mediated hormone recognition and Gβ interaction by the human melanocortin-1 receptor. Cell Res 2021; 31:1061-1071. [PMID: 34453129 PMCID: PMC8486761 DOI: 10.1038/s41422-021-00557-y] [Citation(s) in RCA: 35] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Accepted: 07/30/2021] [Indexed: 02/07/2023] Open
Abstract
Melanocortins are peptide hormones critical for the regulation of stress response, energy homeostasis, inflammation, and skin pigmentation. Their functions are mediated by five G protein-coupled receptors (MC1R-MC5R), predominately through the stimulatory G protein (Gs). MC1R, the founding member of melanocortin receptors, is mainly expressed in melanocytes and is involved in melanogenesis. Dysfunction of MC1R is associated with the development of melanoma and skin cancer. Here we present three cryo-electron microscopy structures of the MC1R-Gs complexes bound to endogenous hormone α-MSH, a marketed drug afamelanotide, and a synthetic agonist SHU9119. These structures reveal the orthosteric binding pocket for the conserved HFRW motif among melanocortins and the crucial role of calcium ion in ligand binding. They also demonstrate the basis of differential activities among different ligands. In addition, unexpected interactions between MC1R and the Gβ subunit were discovered from these structures. Together, our results elucidate a conserved mechanism of calcium-mediated ligand recognition, a specific mode of G protein coupling, and a universal activation pathway of melanocortin receptors.
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Schihada H, Shekhani R, Schulte G. Quantitative assessment of constitutive G protein-coupled receptor activity with BRET-based G protein biosensors. Sci Signal 2021; 14:eabf1653. [PMID: 34516756 DOI: 10.1126/scisignal.abf1653] [Citation(s) in RCA: 36] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
[Figure: see text].
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Affiliation(s)
- Hannes Schihada
- Section for Receptor Biology and Signaling, Department of Physiology and Pharmacology, Karolinska Institutet, Biomedicum, Solnavägen 9, SE-17165 Stockholm, Sweden
| | - Rawan Shekhani
- Section for Receptor Biology and Signaling, Department of Physiology and Pharmacology, Karolinska Institutet, Biomedicum, Solnavägen 9, SE-17165 Stockholm, Sweden
| | - Gunnar Schulte
- Section for Receptor Biology and Signaling, Department of Physiology and Pharmacology, Karolinska Institutet, Biomedicum, Solnavägen 9, SE-17165 Stockholm, Sweden
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5
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Lavogina D, Laasfeld T, Tahk MJ, Kukk O, Allikalt A, Kopanchuk S, Rinken A. cAMP Biosensor Assay Using BacMam Expression System: Studying the Downstream Signaling of LH/hCG Receptor Activation. Methods Mol Biol 2021; 2268:179-192. [PMID: 34085269 DOI: 10.1007/978-1-0716-1221-7_12] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Cyclic adenosine monophosphate (cAMP) serves as a second messenger for numerous G-protein-coupled receptors. Changes in cellular cAMP levels reflect the biological activity of various GPCR-specific agents, including protein hormones. cAMP biosensors based on detection of Förster-type resonance energy transfer (FRET) offer unique advantages including the ratiometric nature of measurement, adjustable affinity toward detected molecule, capability of monitoring kinetics of cAMP release, and compatibility with the multi-well format and fluorescence plate reader platforms. In this chapter, we introduce the optimized version of the previously reported method to achieve sufficient and reproducible level of cAMP biosensor protein expression with the means of BacMam transduction system. As a practical challenge, we address the applicability of the designed assay for screening of biological activity of human hormones, including human chorionic gonadotropin (hCG) bearing different posttranslational modifications.
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Affiliation(s)
- Darja Lavogina
- Institute of Chemistry, University of Tartu, Tartu, Estonia
- University of Tartu, Institute of Clinical Medicine, Clinic of Hematology and Oncology, Tartu, Estonia
- Competence Centre on Reproductive Medicine & Biology, Tartu, Estonia
| | - Tõnis Laasfeld
- Institute of Chemistry, University of Tartu, Tartu, Estonia
| | | | - Olga Kukk
- Institute of Chemistry, University of Tartu, Tartu, Estonia
- Competence Centre on Reproductive Medicine & Biology, Tartu, Estonia
| | - Anni Allikalt
- Institute of Chemistry, University of Tartu, Tartu, Estonia
| | | | - Ago Rinken
- Institute of Chemistry, University of Tartu, Tartu, Estonia.
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6
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Israeli H, Degtjarik O, Fierro F, Chunilal V, Gill AK, Roth NJ, Botta J, Prabahar V, Peleg Y, Chan LF, Ben-Zvi D, McCormick PJ, Niv MY, Shalev-Benami M. Structure reveals the activation mechanism of the MC4 receptor to initiate satiation signaling. Science 2021; 372:808-814. [PMID: 33858992 DOI: 10.1126/science.abf7958] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Accepted: 04/08/2021] [Indexed: 12/18/2022]
Abstract
Obesity is a global epidemic that causes morbidity and impaired quality of life. The melanocortin receptor 4 (MC4R) is at the crux of appetite, energy homeostasis, and body-weight control in the central nervous system and is a prime target for anti-obesity drugs. Here, we present the cryo-electron microscopy (cryo-EM) structure of the human MC4R-Gs signaling complex bound to the agonist setmelanotide, a cyclic peptide recently approved for the treatment of obesity. The work reveals the mechanism of MC4R activation, highlighting a molecular switch that initiates satiation signaling. In addition, our findings indicate that calcium (Ca2+) is required for agonist, but not antagonist, efficacy. These results fill a gap in the understanding of MC4R activation and could guide the design of future weight-management drugs.
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Affiliation(s)
- Hadar Israeli
- Department of Chemical and Structural Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
- Department of Developmental Biology and Cancer Research, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Oksana Degtjarik
- Department of Chemical and Structural Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Fabrizio Fierro
- The Faculty of Agriculture, Food and Environment, The Hebrew University, Rehovot, Israel
- The Fritz Haber Center for Molecular Dynamics, The Hebrew University, Jerusalem, Israel
| | - Vidicha Chunilal
- Centre for Endocrinology, William Harvey Research Institute, Barts and the London School of Medicine, Queen Mary, University of London, Charterhouse Square, London, UK
| | - Amandeep Kaur Gill
- Centre for Endocrinology, William Harvey Research Institute, Barts and the London School of Medicine, Queen Mary, University of London, Charterhouse Square, London, UK
| | - Nicolas J Roth
- Centre for Endocrinology, William Harvey Research Institute, Barts and the London School of Medicine, Queen Mary, University of London, Charterhouse Square, London, UK
| | - Joaquin Botta
- Centre for Endocrinology, William Harvey Research Institute, Barts and the London School of Medicine, Queen Mary, University of London, Charterhouse Square, London, UK
| | - Vadivel Prabahar
- Department of Chemical and Structural Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Yoav Peleg
- Structural Proteomics Unit (SPU), Life Sciences Core Facilities (LSCF), Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Li F Chan
- Centre for Endocrinology, William Harvey Research Institute, Barts and the London School of Medicine, Queen Mary, University of London, Charterhouse Square, London, UK
| | - Danny Ben-Zvi
- Department of Developmental Biology and Cancer Research, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel.
| | - Peter J McCormick
- Centre for Endocrinology, William Harvey Research Institute, Barts and the London School of Medicine, Queen Mary, University of London, Charterhouse Square, London, UK.
| | - Masha Y Niv
- The Faculty of Agriculture, Food and Environment, The Hebrew University, Rehovot, Israel.
- The Fritz Haber Center for Molecular Dynamics, The Hebrew University, Jerusalem, Israel
| | - Moran Shalev-Benami
- Department of Chemical and Structural Biology, Weizmann Institute of Science, Rehovot 7610001, Israel.
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7
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Laasfeld T, Ehrminger R, Tahk MJ, Veiksina S, Kõlvart KR, Min M, Kopanchuk S, Rinken A. Budded baculoviruses as a receptor display system to quantify ligand binding with TIRF microscopy. NANOSCALE 2021; 13:2436-2447. [PMID: 33464268 DOI: 10.1039/d0nr06737g] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Studying mechanisms of receptor-ligand interactions has remained challenging due to several limitations of different measurement methods. Here we present a total internal reflection fluorescence microscopy-based method that maintains the right balance between retaining the receptors in the natural lipid environment, sufficient throughput for ligand screening, high sensitivity, and offering more detailed view into the ligand-binding process. The novel method combines G protein-coupled receptor display in budded baculovirus particles and the immobilization of the particles to a functionalized coverslip. We adapted and validated the functionalized coverslip preparation process to achieve selective immobilization of budded baculovirus particles. The selectivity of budded baculovirus immobilization was validated with budded baculovirus particles displaying either Frizzled 6 receptors labeled with mCherry or neuropeptide Y Y1 receptors. To scale the system for ligand binding assays, we developed both open-source multiwell systems and image analysis software SPOTNIC for flexible assay design. The neuropeptide Y Y1 receptor was used for further receptor-ligand binding studies with high-affinity TAMRA labeled fluorescent ligand UR-MC026. The affinities of the fluorescent ligand and four unlabeled ligands (BIBO3304, UR-MK299, PYY, pNPY) were obtained with the developed method and followed a similar trend with both the parallel measurements with fluorescence anisotropy method and the data published earlier. The novel method could be extended for various advanced assays utilizing multidimensional detection modes, integrating super-resolution methods for single molecule detection and microfluidic devices for kinetic measurements.
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Affiliation(s)
- Tõnis Laasfeld
- University of Tartu, Institute of Chemistry, Ravila 14a, 50411, Tartu, Estonia.
| | - Robin Ehrminger
- University of Tartu, Institute of Chemistry, Ravila 14a, 50411, Tartu, Estonia. and Tallinn University of Technology, Thomas Johann Seebeck Department of Electronics, Ehitajate Tee 5, 19086, Tallinn, Estonia
| | - Maris-Johanna Tahk
- University of Tartu, Institute of Chemistry, Ravila 14a, 50411, Tartu, Estonia.
| | - Santa Veiksina
- University of Tartu, Institute of Chemistry, Ravila 14a, 50411, Tartu, Estonia.
| | - Karl Rene Kõlvart
- University of Tartu, Institute of Chemistry, Ravila 14a, 50411, Tartu, Estonia.
| | - Mart Min
- Tallinn University of Technology, Thomas Johann Seebeck Department of Electronics, Ehitajate Tee 5, 19086, Tallinn, Estonia
| | - Sergei Kopanchuk
- University of Tartu, Institute of Chemistry, Ravila 14a, 50411, Tartu, Estonia.
| | - Ago Rinken
- University of Tartu, Institute of Chemistry, Ravila 14a, 50411, Tartu, Estonia.
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8
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Veiksina S, Tahk MJ, Laasfeld T, Link R, Kopanchuk S, Rinken A. Fluorescence Anisotropy-Based Assay for Characterization of Ligand Binding Dynamics to GPCRs: The Case of Cy3B-Labeled Ligands Binding to MC 4 Receptors in Budded Baculoviruses. Methods Mol Biol 2021; 2268:119-136. [PMID: 34085265 DOI: 10.1007/978-1-0716-1221-7_8] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
During the past decade, fluorescence methods have become valuable tools for characterizing ligand binding to G protein-coupled receptors (GPCRs). However, only a few of the assays enable studying wild-type receptors and monitor the ligand binding in real time. One of the approaches that is inherently suitable for this purpose is the fluorescence anisotropy (FA) assay. In the FA assay, the change of ligand's rotational freedom connected with its binding to the receptor can be monitored with a conventional fluorescence plate reader equipped with suitable optical filters. To achieve the high receptor concentration required for the assay and the low autofluorescence levels essential for reliable results, budded baculoviruses that display GPCRs on their surfaces can be used. The monitoring process generates a substantial amount of kinetic data, which is usually stored as a proprietary file format limiting the flexibility of data analysis. To solve this problem, we propose the use of the data curation software Aparecium ( http://gpcr.ut.ee/aparecium.html ), which integrates experimental data with metadata in a Minimum Information for Data Analysis in Systems Biology (MIDAS) format. Aparecium enables data export to different software packages for fitting to suitable kinetic or equilibrium models. A combination of the FA assay with the novel data analysis strategy is suitable for screening new active compounds, but also for modeling complex systems of ligand binding to GPCRs. We present the proposed approach using different fluorescent probes and assay types to characterize ligand binding to melanocortin 4 (MC4) receptor.
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Affiliation(s)
- Santa Veiksina
- Institute of Chemistry, University of Tartu, Tartu, Estonia
| | | | - Tõnis Laasfeld
- Institute of Chemistry, University of Tartu, Tartu, Estonia
| | - Reet Link
- Institute of Chemistry, University of Tartu, Tartu, Estonia
| | | | - Ago Rinken
- Institute of Chemistry, University of Tartu, Tartu, Estonia.
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9
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BRET- and fluorescence anisotropy-based assays for real-time monitoring of ligand binding to M 2 muscarinic acetylcholine receptors. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2020; 1868:118930. [PMID: 33347921 DOI: 10.1016/j.bbamcr.2020.118930] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Revised: 11/26/2020] [Accepted: 12/11/2020] [Indexed: 12/14/2022]
Abstract
BRET and fluorescence anisotropy (FA) are two fluorescence-based techniques used for the characterization of ligand binding to G protein-coupled receptors (GPCRs) and both allow monitoring of ligand binding in real time. In this study, we present the first direct comparison of BRET-based and FA-based binding assays using the human M2 muscarinic acetylcholine receptor (M2R) and two TAMRA (5-carboxytetramethylrhodamine)-labeled fluorescent ligands as a model system. The determined fluorescent ligand affinities from both assays were in good agreement with results obtained from radioligand competition binding experiments. The assays yielded real-time kinetic binding data revealing differences in the mechanism of binding for the investigated fluorescent probes. Furthermore, the investigation of various unlabeled M2R ligands yielded pharmacological profiles in accordance with earlier reported data. Taken together, this study showed that BRET- and FA-based binding assays represent valuable alternatives to radioactivity-based methods for screening purposes and for a precise characterization of binding kinetics supporting the exploration of binding mechanisms.
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10
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Yang LK, Tao YX. Alanine Scanning Mutagenesis of the DRYxxI Motif and Intracellular Loop 2 of Human Melanocortin-4 Receptor. Int J Mol Sci 2020; 21:ijms21207611. [PMID: 33076233 PMCID: PMC7589821 DOI: 10.3390/ijms21207611] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Revised: 10/10/2020] [Accepted: 10/11/2020] [Indexed: 12/15/2022] Open
Abstract
The melanocortin-4 receptor (MC4R) is a member of the G-protein-coupled receptor (GPCR) superfamily, which has been extensively studied in obesity pathogenesis due to its critical role in regulating energy homeostasis. Both the Gs-cAMP and ERK1/2 cascades are known as important intracellular signaling pathways initiated by the MC4R. The DRYxxI motif at the end of transmembrane domain 3 and the intracellular loop 2 (ICL2) are thought to be crucial for receptor function in several GPCRs. To study the functions of this domain in MC4R, we performed alanine-scanning mutagenesis on seventeen residues. We showed that one residue was critical for receptor cell surface expression. Eight residues were important for ligand binding. Mutations of three residues impaired Gs-cAMP signaling without changing the binding properties. Investigation on constitutive activities of all the mutants in the cAMP pathway revealed that six residues were involved in constraining the receptor in inactive states and five residues were important for receptor activation in the absence of an agonist. In addition, mutations of four residues impaired the ligand-stimulated ERK1/2 signaling pathway without affecting the binding properties. We also showed that some mutants were biased to the Gs-cAMP or ERK1/2 signaling pathway. In summary, we demonstrated that the DRYxxI motif and ICL2 were important for MC4R function.
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11
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Huang XP, Kenakin TP, Gu S, Shoichet BK, Roth BL. Differential Roles of Extracellular Histidine Residues of GPR68 for Proton-Sensing and Allosteric Modulation by Divalent Metal Ions. Biochemistry 2020; 59:3594-3614. [PMID: 32865988 DOI: 10.1021/acs.biochem.0c00576] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
GPR68, an orphan G-protein coupled receptor, senses protons, couples to multiple G-proteins, and is also activated or inhibited by divalent metal ions. It has seven extracellular histidine residues, although it is not clear how these histidine residues play a role in both proton-sensing and metal ion modulation. Here we demonstrate that divalent metal ions are allosteric modulators that can activate or inhibit proton activity in a concentration- and pH-dependent manner. We then show that single histidine mutants have differential and varying degrees of effects on proton-sensing and metal ion modulation. Some histidine residues play dual roles in proton-sensing and metal ion modulation, while others are important in one or the other but not both. Two extracellular disulfide bonds are predicted to constrain histidine residues to be spatially close to each other. Combining histidine mutations leads to reduced proton activity and resistance to metal ion modulation, while breaking the less conserved disulfide bond results in a more severe reduction in proton-sensing over metal modulation. The small-molecule positive allosteric modulators (PAMs) ogerin and lorazepam are not affected by these mutations and remain active at mutants with severely reduced proton activity or are resistant to metal ion modulation. These results suggest GPR68 possesses two independent allosteric modulation systems, one through interaction with divalent metal ions at the extracellular surface and another through small-molecule PAMs in the transmembrane domains. A new GPR68 model is developed to accommodate the findings which could serve as a template for further studies and ligand discovery by virtual ligand docking.
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Affiliation(s)
| | | | - Shuo Gu
- Department of Pharmaceutical Science, University of California, San Francisco, California 94158, United States
| | - Brian K Shoichet
- Department of Pharmaceutical Science, University of California, San Francisco, California 94158, United States
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12
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Structural Complexity and Plasticity of Signaling Regulation at the Melanocortin-4 Receptor. Int J Mol Sci 2020; 21:ijms21165728. [PMID: 32785054 PMCID: PMC7460885 DOI: 10.3390/ijms21165728] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2020] [Revised: 08/03/2020] [Accepted: 08/06/2020] [Indexed: 02/06/2023] Open
Abstract
The melanocortin-4 receptor (MC4R) is a class A G protein-coupled receptor (GPCR), essential for regulation of appetite and metabolism. Pathogenic inactivating MC4R mutations are the most frequent cause of monogenic obesity, a growing medical and socioeconomic problem worldwide. The MC4R mediates either ligand-independent or ligand-dependent signaling. Agonists such as α-melanocyte-stimulating hormone (α-MSH) induce anorexigenic effects, in contrast to the endogenous inverse agonist agouti-related peptide (AgRP), which causes orexigenic effects by suppressing high basal signaling activity. Agonist action triggers the binding of different subtypes of G proteins and arrestins, leading to concomitant induction of diverse intracellular signaling cascades. An increasing number of experimental studies have unraveled molecular properties and mechanisms of MC4R signal transduction related to physiological and pathophysiological aspects. In addition, the MC4R crystal structure was recently determined at 2.75 Å resolution in an inactive state bound with a peptide antagonist. Underpinned by structural homology models of MC4R complexes simulating a presumably active-state conformation compared to the structure of the inactive state, we here briefly summarize the current understanding and key players involved in the MC4R switching process between different activity states. Finally, these perspectives highlight the complexity and plasticity in MC4R signaling regulation and identify gaps in our current knowledge.
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