1
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Ashton AW. Preparing to strike: Acute events in signaling by the serpentine receptor for thromboxane A 2. Pharmacol Ther 2023:108478. [PMID: 37321373 DOI: 10.1016/j.pharmthera.2023.108478] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2023] [Revised: 05/31/2023] [Accepted: 06/07/2023] [Indexed: 06/17/2023]
Abstract
Over the last two decades, awareness of the (patho)physiological roles of thromboxane A2 signaling has been greatly extended. From humble beginnings as a short-lived stimulus that activates platelets and causes vasoconstriction to a dichotomous receptor system involving multiple endogenous ligands capable of modifying tissue homeostasis and disease generation in almost every tissue of the body. Thromboxane A2 receptor (TP) signal transduction is associated with the pathogenesis of cancer, atherosclerosis, heart disease, asthma, and host response to parasitic infection amongst others. The two receptors mediating these cellular responses (TPα and TPβ) are derived from a single gene (TBXA2R) through alternative splicing. Recently, knowledge about the mechanism(s) of signal propagation by the two receptors has undergone a revolution in understanding. Not only have the structural relationships associated with G-protein coupling been established but the modulation of that signaling by post-translational modification to the receptor has come sharply into focus. Moreover, the signaling of the receptor unrelated to G-protein coupling has become a burgeoning field of endeavor with over 70 interacting proteins currently identified. These data are reshaping the concept of TP signaling from a mere guanine nucleotide exchange factors for Gα activation to a nexus for the convergence of diverse and poorly characterized signaling pathways. This review summarizes the advances in understanding in TP signaling, and the potential for new growth in a field that after almost 50 years is finally coming of age.
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Affiliation(s)
- Anthony W Ashton
- Division of Cardiovascular Medicine, Lankenau Institute for Medical Research, Rm 128, 100 E Lancaster Ave, Wynnewood, PA 19096, USA; Division of Perinatal Research, Kolling Institute of Medical Research, Faculty of Medicine and Health, University of Sydney, St Leonards, NSW 2065, Australia.
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2
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Li QY, Li Y, Inoue A, Lu R, Xu A, Ruan KH. Reversing thromboxane A2 receptor activity from calcium to cAMP signaling by shifting Gαq to Gαs covalently linked to the receptor. Biochem Eng J 2022. [DOI: 10.1016/j.bej.2022.108465] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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3
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Advances in extracellular ligand recognition sites on prostanoid receptors. Future Med Chem 2018; 10:979-981. [DOI: 10.4155/fmc-2017-0319] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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4
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Hadianawala M, Mahapatra AD, Yadav JK, Datta B. Molecular docking, molecular modeling, and molecular dynamics studies of azaisoflavone as dual COX-2 inhibitors and TP receptor antagonists. J Mol Model 2018; 24:69. [DOI: 10.1007/s00894-018-3620-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Accepted: 02/11/2018] [Indexed: 10/17/2022]
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5
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Akasaka H, Thaliachery N, Zheng X, Blumenthal M, Nikhar S, Murdoch EE, Ling Q, Ruan KH. The key residue within the second extracellular loop of human EP3 involved in selectively turning down PGE 2- and retaining PGE 1-mediated signaling in live cells. Arch Biochem Biophys 2017; 616:20-29. [PMID: 28065721 DOI: 10.1016/j.abb.2016.12.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Revised: 11/15/2016] [Accepted: 12/02/2016] [Indexed: 10/20/2022]
Abstract
Key residues and binding mechanisms of PGE1 and PGE2 on prostanoid receptors are poorly understood due to the lack of X-ray structures for the receptors. We constructed a human EP3 (hEP3) model through integrative homology modeling using the X-ray structure of the β2-adrenergic receptor transmembrane domain and NMR structures of the thromboxane A2 receptor extracellular loops. PGE1 and PGE2 docking into the hEP3 model showed differing configurations within the extracellular ligand recognition site. While PGE2 could form possible binding contact with S211, PGE1 is unable to form similar contacts. Therefore, S211 could be the critical residue for PGE2 recognition, but is not a significant for PGE1. This prediction was confirmed using HEK293 cells transfected with hEP3 S211L cDNA. The S211L cells lost PGE2 binding and signaling. Interestingly, the S211L cells retained PGE1-mediated signaling. It indicates that S211 within the second extracellular loop is a key residue involved in turning down PGE2 signaling. Our study provided information that S211L within EP3 is the key residue to distinguish PGE1 and PGE2 binding to mediate diverse biological functions at the initial recognition step. The S211L mutant could be used as a model for studying the binding mechanism and signaling pathway specifically mediated by PGE1.
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Affiliation(s)
- Hironari Akasaka
- Center for Experimental Therapeutics and Pharmacoinformatics and Department of Pharmacological and Pharmaceutical Sciences, University of Houston College of Pharmacy, Houston, TX 77204-5037, USA
| | - Natasha Thaliachery
- Center for Experimental Therapeutics and Pharmacoinformatics and Department of Pharmacological and Pharmaceutical Sciences, University of Houston College of Pharmacy, Houston, TX 77204-5037, USA
| | - Xianghai Zheng
- Center for Experimental Therapeutics and Pharmacoinformatics and Department of Pharmacological and Pharmaceutical Sciences, University of Houston College of Pharmacy, Houston, TX 77204-5037, USA
| | - Marissa Blumenthal
- Center for Experimental Therapeutics and Pharmacoinformatics and Department of Pharmacological and Pharmaceutical Sciences, University of Houston College of Pharmacy, Houston, TX 77204-5037, USA
| | - Sameer Nikhar
- Center for Experimental Therapeutics and Pharmacoinformatics and Department of Pharmacological and Pharmaceutical Sciences, University of Houston College of Pharmacy, Houston, TX 77204-5037, USA
| | - Emma E Murdoch
- Center for Experimental Therapeutics and Pharmacoinformatics and Department of Pharmacological and Pharmaceutical Sciences, University of Houston College of Pharmacy, Houston, TX 77204-5037, USA
| | - Qinglan Ling
- Center for Experimental Therapeutics and Pharmacoinformatics and Department of Pharmacological and Pharmaceutical Sciences, University of Houston College of Pharmacy, Houston, TX 77204-5037, USA
| | - Ke-He Ruan
- Center for Experimental Therapeutics and Pharmacoinformatics and Department of Pharmacological and Pharmaceutical Sciences, University of Houston College of Pharmacy, Houston, TX 77204-5037, USA
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6
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Cohen LS, Fracchiolla KE, Becker J, Naider F. Invited review GPCR structural characterization: Using fragments as building blocks to determine a complete structure. Biopolymers 2014; 102:223-43. [DOI: 10.1002/bip.22490] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2014] [Revised: 03/24/2014] [Accepted: 03/27/2014] [Indexed: 12/30/2022]
Affiliation(s)
- Leah S. Cohen
- Department of Chemistry; The College of Staten Island, City University of New York (CUNY); Staten Island NY 10314
| | - Katrina E. Fracchiolla
- Department of Chemistry; The College of Staten Island, City University of New York (CUNY); Staten Island NY 10314
| | - Jeff Becker
- Department of Microbiology; University of Tennessee; Knoxville TN 37996
| | - Fred Naider
- Department of Chemistry; The College of Staten Island, City University of New York (CUNY); Staten Island NY 10314
- Department of Biochemistry; The Graduate Center; CUNY NY 10016-4309
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7
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Parrill AL. Computational Design and Experimental Characterization of GPCR Segment Models. Methods Enzymol 2013; 522:81-95. [DOI: 10.1016/b978-0-12-407865-9.00005-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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8
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Caroccia KE, Estephan R, Cohen LS, Arshava B, Hauser M, Zerbe O, Becker JM, Naider F. Expression and biophysical analysis of a triple-transmembrane domain-containing fragment from a yeast G protein-coupled receptor. Biopolymers 2011; 96:757-71. [DOI: 10.1002/bip.21614] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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9
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Abstract
G protein-coupled receptors (GPCRs) comprise a large class of transmembrane proteins that play critical roles in both normal physiology and pathophysiology. These critical roles offer targets for therapeutic intervention, as exemplified by the substantial fraction of current pharmaceutical agents that target members of this family. Tremendous contributions to our understanding of GPCR structure and dynamics have come from both indirect and direct structural characterization techniques. Key features of GPCR conformations derived from both types of characterization techniques are reviewed.
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Affiliation(s)
- Abby L. Parrill
- Department of Chemistry, The University of Memphis, Memphis, TN 38152, USA
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +1-901-678-2638; Fax: +1-901-678-3447
| | - Debra L. Bautista
- Christian Brothers High School, 5900 Walnut Grove Road, Memphis, TN 38120, USA; E-Mail: (D.L.B.)
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10
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Yeagle PL, Albert AD. Membrane protein fragments reveal both secondary and tertiary structure of membrane proteins. Methods Mol Biol 2010; 654:283-301. [PMID: 20665272 DOI: 10.1007/978-1-60761-762-4_15] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Structural data on membrane proteins, while crucial to understanding cellular function, are scarce due to difficulties in applying to membrane proteins the common techniques of structural biology. Fragments of membrane proteins have been shown to reflect, in many cases, the secondary structure of the parent protein with fidelity and are more amenable to study. This chapter provides many examples of how the study of membrane protein fragments has provided new insight into the structure of the parent membrane protein.
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Affiliation(s)
- Philip L Yeagle
- Office of the Dean of Arts & Sciences, Rutgers University, Newark, NJ, USA.
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11
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Ruan KH, Cervantes V, Wu J. Ligand-specific conformation determines agonist activation and antagonist blockade in purified human thromboxane A2 receptor. Biochemistry 2009; 48:3157-65. [PMID: 19170518 DOI: 10.1021/bi801443g] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The binding of an agonist to a G protein-coupled receptor (GPCR) causes its coupling to different G proteins, which mediate signaling. However, the binding of an antagonist to the same site of the GPCR could not induce coupling. To understand the molecular mechanism involved, the structural flexibility of the purified human thromboxane A2 receptor (TP) was characterized by spectroscopic approaches, while bound to an agonist or antagonist. Circular dichroism not only revealed that the purified TP adopted more than 50% helical conformation in solution but also showed that the antagonist, SQ29,548, could induce more of a beta-sheet structure in the TP than that of the agonist, U46619. Also, fluorescence studies showed that the antagonist induced the intrinsic Trp fluorescence signal change more than the agonist. Furthermore, three of the nine tryptophan residues involved in the different ligand-based structural changes were demonstrated by NMR spectroscopy. Low pH-induced changes in the receptor conformation and molecular interaction field dramatically increased the agonist binding but did not significantly affect the antagonist binding. Different conformational changes were also observed in the TP reconstituted into phosphatidylcholine/phosphatidylserine/phosphatydylethanolamine-formed liposomes. These studies are the first to show a possible mechanism of the ligand-specific conformation-dependent agonist activation and antagonist blockage in the GPCR.
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Affiliation(s)
- Ke-He Ruan
- The Center for Experimental Therapeutics and Pharmacoinformatics, Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, 521 Science & Research Building 2, University of Houston, Houston, Texas 77004-5037, USA.
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12
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Ruan KH, Cervantes V, Wu J. A simple, quick, and high-yield preparation of the human thromboxane A2 receptor in full size for structural studies. Biochemistry 2008; 47:6819-26. [PMID: 18529068 PMCID: PMC2581465 DOI: 10.1021/bi702501g] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Human thromboxane A2 receptor (TP), a G protein-coupled receptor (GPCR), is one of the most promising targets for developing the next generation of anti-thrombosis and hypertension drugs. However, obtaining a sufficient amount of the full-sized and active membrane protein has been the major obstacle for structural elucidation that reveals the molecular mechanisms of the receptor activation and drug designs. Here we report an approach for the simple, quick, and high-yield preparation of the purified and active full-sized TP in an amount suitable for structural studies. Glycosylated human TP was highly expressed in Sf-9 cells using an optimized baculovirus (BV) expression system. The active receptor was extracted and solubilized by different detergents for comparison and was finally purified to a nearly single band with a ratio of 1:0.9 +/- 0.05 (ligand:receptor molecule) in ligand binding using a Ni column with a relatively low yield. However, a high-yield purification (milligram quantity) of the TP protein, from a modulate scale of transfected Sf-9 cell culture, has been achieved by quick and simple purification steps, which include DNA digestion, dodecyl-maltoside detergent extraction, centrifugation, and FPLC purification. The purity and quantity of the purified TP, using the high-yield approach, were suitable for protein structural studies as evidenced by SDS-PAGE, Western blot analyses, ligand binding assays, and a feasibility test using high-resolution one-dimensional and two-dimensional (1)H NMR spectroscopic analyses. These studies provide a basis for the high-yield expression and purification of the GPCR for the structural and functional characterization using biophysics approaches.
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MESH Headings
- Animals
- Baculoviridae/genetics
- Cell Line
- Chlorocebus aethiops
- Cloning, Molecular
- DNA, Complementary/genetics
- Gene Expression
- Genetic Vectors/genetics
- Humans
- Ligands
- Molecular Sequence Data
- Nuclear Magnetic Resonance, Biomolecular
- Protein Binding
- Protein Processing, Post-Translational
- Receptors, Thromboxane A2, Prostaglandin H2/chemistry
- Receptors, Thromboxane A2, Prostaglandin H2/genetics
- Receptors, Thromboxane A2, Prostaglandin H2/isolation & purification
- Receptors, Thromboxane A2, Prostaglandin H2/metabolism
- Spodoptera
- Time Factors
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Affiliation(s)
- Ke-He Ruan
- Department of Pharmacological and Pharmaceutical Sciences, Center for Experimental Therapeutics and PharmacoInformatics, University of Houston, Houston, Texas 77204-5037, USA.
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13
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Ni F, So SP, Cervantes V, Ruan KH. A profile of the residues in the second extracellular loop that are critical for ligand recognition of human prostacyclin receptor. FEBS J 2008; 275:128-37. [PMID: 18042246 PMCID: PMC3046732 DOI: 10.1111/j.1742-4658.2007.06183.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The residues in the second extracellular loop (eLP2) of the prostanoid receptors, which are important for specific ligand recognition, were previously predicted in our earlier studies of the thromboxane A2 receptor (TP) using a combination of NMR spectroscopy and recombinant protein approaches. To further test this hypothesis, another prostanoid receptor, the prostacyclin receptor (IP), which has opposite biological characteristics to that of TP, was used as a model for these studies. A set of recombinant human IPs with site-directed mutations at the nonconserved eLP2 residues were constructed using an Ala-scanning approach, and then expressed in HEK293 and COS-7 cells. The expression levels of the recombinant receptors were six-fold higher in HEK293 cells than in COS-7 cells. The residues important for ligand recognition and binding within the N-terminal segment (G159, Q162, and C165) and the C-terminal segment (L172, R173, M174, and P179) of IP eLP2 were identified by mutagenesis analyses. The molecular mechanisms for the specific ligand recognition of IP were further demonstrated by specific site-directed mutagenesis using different amino acid residues with unique chemical properties for the key residues Q162, L172, R173, and M174. A comparison with the corresponding functional residues identified in TP eLP2 revealed that three (Q162, R173, and M174) of the four residues are nonconserved, and these are proposed to be involved in specific ligand recognition. We discuss the importance of G159 and P179 in ligand recognition through configuration of the loop conformation is discussed. These studies have further indicated that characterization of the residues in the eLP2 regions for all eight prostanoid receptors could be an effective approach for uncovering the molecular mechanisms of the ligand selectivities of the G-protein-coupled receptors.
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Affiliation(s)
- Feng Ni
- The Department of Pharmacological and Pharmaceutical Sciences, and The Center for Experimental Therapeutics and PharmacoInformatics, University of Houston, TX 77204-5037, USA
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14
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Musial-Siwek M, Kendall DA, Yeagle PL. Solution NMR of signal peptidase, a membrane protein. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1778:937-44. [PMID: 18177734 DOI: 10.1016/j.bbamem.2007.11.013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2007] [Revised: 10/09/2007] [Accepted: 11/26/2007] [Indexed: 11/16/2022]
Abstract
Useful solution nuclear magnetic resonance (NMR) data can be obtained from full-length, enzymatically active type I signal peptidase (SPase I), an integral membrane protein, in detergent micelles. Signal peptidase has two transmembrane segments, a short cytoplasmic loop, and a 27-kD C-terminal catalytic domain. It is a critical component of protein transport systems, recognizing and cleaving amino-terminal signal peptides from preproteins during the final stage of their export. Its structure and interactions with the substrate are of considerable interest, but no three-dimensional structure of the whole protein has been reported. The structural analysis of intact membrane proteins has been challenging and only recently has significant progress been achieved using NMR to determine membrane protein structure. Here we employ NMR spectroscopy to study the structure of the full-length SPase I in dodecylphosphocholine detergent micelles. HSQC-TROSY spectra showed resonances corresponding to approximately 3/4 of the 324 residues in the protein. Some sequential assignments were obtained from the 3D HNCACB, 3D HNCA, and 3D HN(CO) TROSY spectra of uniformly 2H, 13C, 15N-labeled full-length SPase I. The assigned residues suggest that the observed spectrum is dominated by resonances arising from extramembraneous portions of the protein and that the transmembrane domain is largely absent from the spectra. Our work elucidates some of the challenges of solution NMR of large membrane proteins in detergent micelles as well as the future promise of these kinds of studies.
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Affiliation(s)
- Monika Musial-Siwek
- Department of Molecular and Cell Biology, The University of Connecticut, Storrs, CT 06269, USA
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15
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Wu J, Feng M, Ruan KH. Assembling NMR structures for the intracellular loops of the human thromboxane A2 receptor: implication of the G protein-coupling pocket. Arch Biochem Biophys 2007; 470:73-82. [PMID: 18073117 DOI: 10.1016/j.abb.2007.11.016] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2007] [Revised: 11/14/2007] [Accepted: 11/15/2007] [Indexed: 11/28/2022]
Abstract
It has been reported that the multiple intracellular loops (iLPs) of the thromboxane A(2) receptor (TP) are involved in the receptor G protein coupling. In this study, a high-resolution 2D NMR technique was used to determine the 3D structures of the first, second, and third iLPs of the TP using synthetic peptides constrained into the loop structures. 2D (1)H NMR spectra, TOCSY and NOESY were obtained for the two peptides from proton NMR experiments. The NMR data was processed and assigned through the Felix 2000 program. Standard methods were used to acquire sequence-specific assignments. Structure calculations were processed through DGII and NMR refinement programs within the Insight II program. We were able to calculate and use the NOE constraints to obtain the superimposed structure of 10 structures for each iLP peptide. The NMR-determined structures of the iLP peptides were used to refine a homology model of the TP. A 3D G-protein-binding cavity, formed by the three intracellular loops, was predicted by the docking of the C-terminal domain of the Galphaq. Based on the structural model and the previous mutagenesis studies, the residues, R130, R60, C223, F138, L360, V361, E358 and Y359, which are important for interaction with the G protein, were further highlighted. These results reveal the possibly important molecular mechanisms in TP signaling and provide structural information to characterize other prostanoid receptor signalings.
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Affiliation(s)
- Jiaxin Wu
- The Center for Experimental Therapeutics and PharmacoInformatics, Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Room 521 Science & Research Building 2, Houston, TX 77204-5037, USA
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16
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Yeagle PL, Albert AD. G-protein coupled receptor structure. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2006; 1768:808-24. [PMID: 17097603 DOI: 10.1016/j.bbamem.2006.10.002] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2006] [Revised: 10/02/2006] [Accepted: 10/05/2006] [Indexed: 11/18/2022]
Abstract
Because of their central role in regulation of cellular function, structure/function relationships for G-protein coupled receptors (GPCR) are of vital importance, yet only recently have sufficient data been obtained to begin mapping those relationships. GPCRs regulate a wide range of cellular processes, including the senses of taste, smell, and vision, and control a myriad of intracellular signaling systems in response to external stimuli. Many diseases are linked to GPCRs. A critical need exists for structural information to inform studies on mechanism of receptor action and regulation. X-ray crystal structures of only one GPCR, in an inactive state, have been obtained to date. However considerable structural information for a variety of GPCRs has been obtained using non-crystallographic approaches. This review begins with a review of the very earliest GPCR structural information, mostly derived from rhodopsin. Because of the difficulty in crystallizing GPCRs for X-ray crystallography, the extensive published work utilizing alternative approaches to GPCR structure is reviewed, including determination of three-dimensional structure from sparse constraints. The available X-ray crystallographic analyses on bovine rhodopsin are reviewed as the only available high-resolution structures for any GPCR. Structural information available on ligand binding to several receptors is included. The limited information on excited states of receptors is also reviewed. It is concluded that while considerable basic structural information has been obtained, more data are needed to describe the molecular mechanism of activation of a GPCR.
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Affiliation(s)
- Philip L Yeagle
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA.
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Ruan CH, Wu J, Ruan KH. A strategy using NMR peptide structures of thromboxane A2 receptor as templates to construct ligand-recognition pocket of prostacyclin receptor. BMC BIOCHEMISTRY 2005; 6:23. [PMID: 16271145 PMCID: PMC1298286 DOI: 10.1186/1471-2091-6-23] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/19/2005] [Accepted: 11/04/2005] [Indexed: 11/10/2022]
Abstract
Background: Prostacyclin receptor (IP) and thromboxane A2 receptor (TP) belong to rhodopsin-type G protein-coupling receptors and respectively bind to prostacyclin and thromboxane A2 derived from arachidonic acid. Recently, we have determined the extracellular loop (eLP) structures of the human TP receptor by 2-D 1H NMR spectroscopy using constrained peptides mimicking the individual eLP segments. The studies have identified the segment along with several residues in the eLP domains important to ligand recognition, as well as proposed a ligand recognition pocket for the TP receptor. Results: The IP receptor shares a similar primary structure in the eLPs with those of the TP receptor. Forty percent residues in the second eLPs of the receptors are identical, which is the major region involved in forming the ligand recognition pocket in the TP receptor. Based on the high homology score, the eLP domains of the IP receptor were constructed by the homology modeling approach using the NMR structures of the TP eLPs as templates, and then configured to the seven transmembrane (TM) domains model constructed using the crystal structure of the bovine rhodopsin as a template. A NMR structure of iloprost was docked into the modeled IP ligand recognition pocket. After dynamic studies, the segments and residues involved in the IP ligand recognition were proposed. A key residue, Arg173 involved in the ligand recognition for the IP receptor, as predicted from the modeling, was confirmed by site-directed mutagenesis. Conclusion: A 3-D model of the human IP receptor was constructed by homology modeling using the crystal structure of bovine rhodopsin TM domains and the NMR structures of the synthetic constrained peptides of the eLP domains of the TP receptor as templates. This strategy can be applied to molecular modeling and the prediction of ligand recognition pockets for other prostanoid receptors.
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MESH Headings
- Amino Acid Sequence
- Animals
- Binding Sites/physiology
- COS Cells
- Cattle
- Chlorocebus aethiops
- Humans
- Ligands
- Models, Molecular
- Molecular Sequence Data
- Nuclear Magnetic Resonance, Biomolecular/methods
- Receptors, Epoprostenol/chemistry
- Receptors, Epoprostenol/genetics
- Receptors, Epoprostenol/metabolism
- Receptors, Thromboxane A2, Prostaglandin H2/chemistry
- Receptors, Thromboxane A2, Prostaglandin H2/genetics
- Receptors, Thromboxane A2, Prostaglandin H2/metabolism
- Sequence Analysis, Protein/methods
- Templates, Genetic
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Affiliation(s)
- Cheng-Huai Ruan
- From the Vascular Biology Research Center and Division of Hematology, Department of Internal Medicine, The University of Texas Health Science Center, Houston, 6431 Fannin St., Houston, Texas 77030, USA
| | - Jaixin Wu
- From the Vascular Biology Research Center and Division of Hematology, Department of Internal Medicine, The University of Texas Health Science Center, Houston, 6431 Fannin St., Houston, Texas 77030, USA
| | - Ke-He Ruan
- From the Vascular Biology Research Center and Division of Hematology, Department of Internal Medicine, The University of Texas Health Science Center, Houston, 6431 Fannin St., Houston, Texas 77030, USA
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18
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Ruan KH, Wu J, So SP, Jenkins LA, Ruan CH. NMR structure of the thromboxane A2 receptor ligand recognition pocket. ACTA ACUST UNITED AC 2004; 271:3006-16. [PMID: 15233797 DOI: 10.1111/j.1432-1033.2004.04232.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To overcome the difficulty of characterizing the structures of the extracellular loops (eLPs) of G protein-coupled receptors (GPCRs) other than rhodopsin, we have explored a strategy to generate a three-dimensional structural model for a GPCR, the thromboxane A(2) receptor. This three-dimensional structure was completed by the assembly of the NMR structures of the computation-guided constrained peptides that mimicked the extracellular loops and connected to the conserved seven transmembrane domains. The NMR structure-based model reveals the structural features of the eLPs, in which the second extracellular loop (eLP(2)) and the disulfide bond between the first extracellular loop (eLP(1)) and eLP(2) play a major role in forming the ligand recognition pocket. The eLP(2) conformation is dynamic and regulated by the oxidation and reduction of the disulfide bond, which affects ligand docking in the initial recognition. The reduced form of the thromboxane A(2) receptor experienced a decrease in ligand binding activity due to the rearrangement of the eLP(2) conformation. The ligand-bound receptor was, however, resistant to the reduction inactivation because the ligand covered the disulfide bond and stabilized the eLP(2) conformation. This molecular mechanism of ligand recognition is the first that may be applied to other prostanoid receptors and other GPCRs.
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MESH Headings
- Amino Acid Sequence
- Animals
- Binding Sites
- Disulfides/chemistry
- Humans
- Ligands
- Models, Molecular
- Molecular Sequence Data
- Nuclear Magnetic Resonance, Biomolecular
- Oxidation-Reduction
- Peptides/chemistry
- Peptides/genetics
- Peptides/metabolism
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Receptors, Thromboxane A2, Prostaglandin H2/chemistry
- Receptors, Thromboxane A2, Prostaglandin H2/genetics
- Receptors, Thromboxane A2, Prostaglandin H2/metabolism
- Sequence Alignment
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Affiliation(s)
- Ke-He Ruan
- Vascular Biology Research Center and Division of Hematology, Department of Internal Medicine, The University of Texas Health Science Center, Houston, TX 77030, USA.
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Ruan KH, Wu J, So SP, Jenkins LA. Evidence of the residues involved in ligand recognition in the second extracellular loop of the prostacyclin receptor characterized by high resolution 2D NMR techniques. Arch Biochem Biophys 2003; 418:25-33. [PMID: 13679079 DOI: 10.1016/s0003-9861(03)00401-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
In previous studies, we have determined the solution structure of the second extracellular loop (eLP(2)) of the human thromboxane A(2) receptor (TP) and identified the residues in the eLP(2) domain involved in ligand recognition, by using a combination of approaches including a constrained synthetic peptide, 2D NMR spectroscopy, and recombinant proteins. These findings led us to hypothesize that the specific ligand recognition sites may be localized in the eLP(2) for all the prostanoid receptors. To test this hypothesis, we have investigated the ligand recognition site for another prostanoid receptor, the prostacyclin receptor (IP), which mediates an opposite biological function compared to that of the TP receptor. The identification of the interaction between the IP receptor and its agonist, iloprost, was achieved with a constrained synthetic peptide mimicking the eLP(2) region of the receptor. The IP eLP(2) segment was designed and synthesized to form a constrained loop, using a homocysteine disulfide bond connecting the ends of the peptide, based on the distance predicted from the IP receptor model created by homology modeling using the crystal structure of bovine rhodopsin as a template. The evidence of the constrained IP eLP(2) interaction with iloprost was found by the identification of the conformational changes of the eLP(2) induced by iloprost using fluorescence spectroscopy, and was further confirmed by 1D and 2D 1H NMR experiments. In addition, the IP eLP(2)-induced structure of iloprost in solution was elucidated through a complete assignment of the 2D 1H NMR spectra for iloprost in the presence of the IP eLP(2) segment. In contrast, no ordered structure was observed in the 2D 1H NMR experiments for iloprost alone in solution. These studies not only identified that the eLP(2) segment of the IP receptor is involved in ligand recognition, but also solved the 3D solution structure of the bound-form of iloprost, which could be used to study the receptor-ligand interaction in structural terms.
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Affiliation(s)
- Ke-He Ruan
- Vascular Biology Research Center and Division of Hematology, Department of Internal Medicine, The University of Texas Health Science Center, Houston, TX 77030, USA.
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