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Trubacova R, Drastichova Z, Novotny J. Biochemical and physiological insights into TRH receptor-mediated signaling. Front Cell Dev Biol 2022; 10:981452. [PMID: 36147745 PMCID: PMC9485831 DOI: 10.3389/fcell.2022.981452] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Accepted: 08/16/2022] [Indexed: 11/13/2022] Open
Abstract
Thyrotropin-releasing hormone (TRH) is an important endocrine agent that regulates the function of cells in the anterior pituitary and the central and peripheral nervous systems. By controlling the synthesis and release of thyroid hormones, TRH affects many physiological functions, including energy homeostasis. This hormone exerts its effects through G protein-coupled TRH receptors, which signal primarily through Gq/11 but may also utilize other G protein classes under certain conditions. Because of the potential therapeutic benefit, considerable attention has been devoted to the synthesis of new TRH analogs that may have some advantageous properties compared with TRH. In this context, it may be interesting to consider the phenomenon of biased agonism and signaling at the TRH receptor. This possibility is supported by some recent findings. Although knowledge about the mechanisms of TRH receptor-mediated signaling has increased steadily over the past decades, there are still many unanswered questions, particularly about the molecular details of post-receptor signaling. In this review, we summarize what has been learned to date about TRH receptor-mediated signaling, including some previously undiscussed information, and point to future directions in TRH research that may offer new insights into the molecular mechanisms of TRH receptor-triggered actions and possible ways to modulate TRH receptor-mediated signaling.
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Effect of thyroxin on cell morphology and hormone secretion of pituitary grafts in rats. Ann Anat 2020; 230:151486. [PMID: 32145383 DOI: 10.1016/j.aanat.2020.151486] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2019] [Revised: 01/30/2020] [Accepted: 02/03/2020] [Indexed: 11/21/2022]
Abstract
INTRODUCTION Growth hormone and prolactin secretion is affected by thyroid hormones. To see if this influence is subsidiary to the hyptothalamus, we investigated the effects of thyroxin (T4) on hormone secretion and histology of sellar pituitaries and pituitary grafts detached from the hypothalamus (autografted or allografted under the kidney capsule). MATERIALS AND METHODS Male Wistar rats were divided into eight groups: control, thyroidectomised, pituitary autografted, pituitary allografted, and four additional groups that were injected with T4 for two weeks, starting four weeks after surgery. At sacrifice, adenohypophysial hormone blood levels were assessed, and tissue from sellar and grafted pituitaries were investigated by histology and electron microscopy. RESULTS Growth hormone and prolactin blood levels, as well as the number of growth hormone immunopositive cells increased in T4-treated groups. Both pituitary auto- and allo-grafts showed lactotroph hyperplasia and displayed spongiform areas containing cells with vesicles in their cytoplasm resembling thyroidectomy cells. This phenomenon was minimized in their respective T4-treated group. Thyroidectomy cells were identified in pituitary grafts, indicating that hypothalamic control was not essential to induce them. DISCUSSION AND CONCLUSION It is intriguing that the pituitary allografted group, even maintaining normal T4 blood levels, developed thyroidectomy cells in their grafts, suggesting that a long- term deficit of vascularization (>4 weeks) prevented T4 from reaching the graft. After 6 weeks, post T4 treatment of two weeks seemed to be the determining factor to minimize thyroidectomy cells in both pituitary autografted + T4 and pituitary allografted + T4 grafts compared to the untreated groups, although more time and/or higher T4 doses may be required to fully restore the euthyroid morphology.
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Meena CL, Thakur A, Nandekar PP, Sharma SS, Sangamwar AT, Jain R. Synthesis and biology of ring-modified l-Histidine containing thyrotropin-releasing hormone (TRH) analogues. Eur J Med Chem 2016; 111:72-83. [PMID: 26854379 DOI: 10.1016/j.ejmech.2016.01.038] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Revised: 01/19/2016] [Accepted: 01/20/2016] [Indexed: 12/18/2022]
Abstract
Thyrotropin-releasing hormone (TRH) analogues bearing halogen groups (Cl, Br and I) at the C-2 and/or C-5 position, and the alkyl group (CH3, C2H5, C3H7, CH2C6H5) at the N-1 position of the imidazole ring of the central histidine residue were synthesized and evaluated for the receptor binding, calcium mobilization (FLIPR), and IP-1 assay at the HEK mTRHR1 and HEK mTRHR2 expressing cell lines. The most promising analogue 7k showed 925-fold selectivity for HEK mTRH-R2 receptor subtype in the IP-1 assay, 272-fold selectivity for HEK mTRH-R2 receptor subtype in the FLIPR assay, and 21-fold receptor binding specificity at HEK TRH-R2 receptor subtype. The peptide 7k was evaluated in vitro in a brain membrane competitive binding assay, and for stability analysis in the presence of TRH-DE, in vivo. The analogue 7k showed decrease in the sleeping time by more than 76% in a pentobarbital-induced sleeping assay, and showed comparatively less elevation in the TSH level in the blood, in vivo. The computational homology modeling of TRH-R1 and TRH-R2 and docking study with the most potent peptide 7k provide impetus to design CNS specific TRH analogues.
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Affiliation(s)
- Chhuttan L Meena
- Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research, Sector 67, S. A. S. Nagar, Punjab 160 062, India
| | - Avinash Thakur
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research, Sector 67, S. A. S. Nagar, Punjab 160 062, India
| | - Prajwal P Nandekar
- Department of Pharmacoinformatics, National Institute of Pharmaceutical Education and Research, Sector 67, S. A. S. Nagar, Punjab 160 062, India
| | - Shyam S Sharma
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research, Sector 67, S. A. S. Nagar, Punjab 160 062, India
| | - Abhay T Sangamwar
- Department of Pharmacoinformatics, National Institute of Pharmaceutical Education and Research, Sector 67, S. A. S. Nagar, Punjab 160 062, India
| | - Rahul Jain
- Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research, Sector 67, S. A. S. Nagar, Punjab 160 062, India.
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Sheftel S, Muratore KE, Black M, Costanzi S. Graph analysis of β2 adrenergic receptor structures: a "social network" of GPCR residues. In Silico Pharmacol 2013; 1:16. [PMID: 25505660 PMCID: PMC4230308 DOI: 10.1186/2193-9616-1-16] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Accepted: 11/25/2013] [Indexed: 02/07/2023] Open
Abstract
Purpose G protein-coupled receptors (GPCRs) are a superfamily of membrane proteins of vast pharmaceutical interest. Here, we describe a graph theory-based analysis of the structure of the β2 adrenergic receptor (β2 AR), a prototypical GPCR. In particular, we illustrate the network of direct and indirect interactions that link each amino acid residue to any other residue of the receptor. Methods Networks of interconnected amino acid residues in proteins are analogous to social networks of interconnected people. Hence, they can be studied through the same analysis tools typically employed to analyze social networks – or networks in general – to reveal patterns of connectivity, influential members, and dynamicity. We focused on the analysis of closeness-centrality, which is a measure of the overall connectivity distance of the member of a network to all other members. Results The residues endowed with the highest closeness-centrality are located in the middle of the seven transmembrane domains (TMs). In particular, they are mostly located in the middle of TM2, TM3, TM6 or TM7, while fewer of them are located in the middle of TM1, TM4 or TM5. At the cytosolic end of TM6, the centrality detected for the active structure is markedly lower than that detected for the corresponding residues in the inactive structures. Moreover, several residues acquire centrality when the structures are analyzed in the presence of ligands. Strikingly, there is little overlap between the residues that acquire centrality in the presence of the ligand in the blocker-bound structures and the agonist-bound structures. Conclusions Our results reflect the fact that the receptor resembles a bow tie, with a rather tight knot of closely interconnected residues and two ends that fan out in two opposite directions: one toward the extracellular space, which hosts the ligand binding cavity, and one toward the cytosol, which hosts the G protein binding cavity. Moreover, they underscore how interaction network is by the conformational rearrangements concomitant with the activation of the receptor and by the presence of agonists or blockers. Electronic supplementary material The online version of this article (doi:10.1186/2193-9616-1-16) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Samuel Sheftel
- Department of Chemistry, American University, 4400 Massachusetts Ave, Northwest, Washington, DC 20016 USA
| | - Kathryn E Muratore
- Department of Chemistry, American University, 4400 Massachusetts Ave, Northwest, Washington, DC 20016 USA
| | - Michael Black
- Department of Computer Science, American University, Northwest, Washington, DC 20016 USA
| | - Stefano Costanzi
- Department of Chemistry, American University, 4400 Massachusetts Ave, Northwest, Washington, DC 20016 USA ; Center for Behavioral Neuroscience, American University, Northwest, Washington, DC 20016 USA
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Kleinau G, Neumann S, Grüters A, Krude H, Biebermann H. Novel insights on thyroid-stimulating hormone receptor signal transduction. Endocr Rev 2013; 34:691-724. [PMID: 23645907 PMCID: PMC3785642 DOI: 10.1210/er.2012-1072] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The TSH receptor (TSHR) is a member of the glycoprotein hormone receptors, a subfamily of family A G protein-coupled receptors. The TSHR is of great importance for the growth and function of the thyroid gland. The TSHR and its endogenous ligand TSH are pivotal proteins with respect to a variety of physiological functions and malfunctions. The molecular events of TSHR regulation can be summarized as a process of signal transduction, including signal reception, conversion, and amplification. The steps during signal transduction from the extra- to the intracellular sites of the cell are not yet comprehensively understood. However, essential new insights have been achieved in recent years on the interrelated mechanisms at the extracellular region, the transmembrane domain, and intracellular components. This review contains a critical summary of available knowledge of the molecular mechanisms of signal transduction at the TSHR, for example, the key amino acids involved in hormone binding or in the structural conformational changes that lead to G protein activation or signaling regulation. Aspects of TSHR oligomerization, signaling promiscuity, signaling selectivity, phenotypes of genetic variations, and potential extrathyroidal receptor activity are also considered, because these are relevant to an understanding of the overall function of the TSHR, including physiological, pathophysiological, and pharmacological perspectives. Directions for future research are discussed.
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Affiliation(s)
- Gunnar Kleinau
- Institute of Experimental Pediatric Endocrinology, Charité-Universitätsmedizin Berlin, Ostring 3, Augustenburger Platz 1, 13353 Berlin, Germany.
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Fanelli F, De Benedetti PG. Update 1 of: computational modeling approaches to structure-function analysis of G protein-coupled receptors. Chem Rev 2011; 111:PR438-535. [PMID: 22165845 DOI: 10.1021/cr100437t] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Francesca Fanelli
- Dulbecco Telethon Institute, University of Modena and Reggio Emilia, via Campi 183, 41125 Modena, Italy.
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Kleinau G, Hoyer I, Kreuchwig A, Haas AK, Rutz C, Furkert J, Worth CL, Krause G, Schülein R. From molecular details of the interplay between transmembrane helices of the thyrotropin receptor to general aspects of signal transduction in family a G-protein-coupled receptors (GPCRs). J Biol Chem 2011; 286:25859-71. [PMID: 21586576 PMCID: PMC3138303 DOI: 10.1074/jbc.m110.196980] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2010] [Revised: 05/10/2011] [Indexed: 12/24/2022] Open
Abstract
Transmembrane helices (TMHs) 5 and 6 are known to be important for signal transduction by G-protein-coupled receptors (GPCRs). Our aim was to characterize the interface between TMH5 and TMH6 of the thyrotropin receptor (TSHR) to gain molecular insights into aspects of signal transduction and regulation. A proline at TMH5 position 5.50 is highly conserved in family A GPCRs and causes a twist in the helix structure. Mutation of the TSHR-specific alanine (Ala-593⁵·⁵⁰) at this position to proline resulted in a 20-fold reduction of cell surface expression. This indicates that TMH5 in the TSHR might have a conformation different from most other family A GPCRs by forming a regular α-helix. Furthermore, linking our own and previous data from directed mutagenesis with structural information led to suggestions of distinct pairs of interacting residues between TMH5 and TMH6 that are responsible for stabilizing either the basal or the active state. Our insights suggest that the inactive state conformation is constrained by a core set of polar interactions among TMHs 2, 3, 6, and 7 and in contrast that the active state conformation is stabilized mainly by non-polar interactions between TMHs 5 and 6. Our findings might be relevant for all family A GPCRs as supported by a statistical analysis of residue properties between the TMHs of a vast number of GPCR sequences.
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Affiliation(s)
- Gunnar Kleinau
- Leibniz-Institut für Molekulare Pharmakologie, 13125 Berlin, Germany.
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Allen MD, Neumann S, Gershengorn MC. Occupancy of both sites on the thyrotropin (TSH) receptor dimer is necessary for phosphoinositide signaling. FASEB J 2011; 25:3687-94. [PMID: 21705666 DOI: 10.1096/fj.11-188961] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The thyroid-stimulating hormone (TSH) receptor signals via G(s) to produce cAMP and via G(q/11) to produce inositol-1,4,5-trisphosphate, which is degraded to inositol monophosphate (IP1; phosphoinositide signaling). The potency of TSH for cAMP signaling is higher than for phosphoinositide signaling, and it was suggested that there are "spare receptors" for cAMP signaling. In a human embryonic kidney macrophage scavenger receptor-expressing (HEK-EM) 293 model system, there are no spare receptors, but the cells still exhibited 100-fold differences in potencies. Dose responses for TSH-stimulated dissociation of prebound (125)I-TSH (negative cooperativity; EC(50)=70 mU/ml), which requires TSH binding to both sites of the TSH receptor (TSHR) homodimer, and TSH-stimulated IP1 production (EC(50)=50 mU/ml) were indistinguishable. Fluorescence resonance energy transfer (FRET) using tagged receptors showed that TSHR formed homodimers and heterodimers with two binding-deficient mutant TSHRs, L252P and C41S. When L252P or C41S was expressed with TSHR, that is, when TSHR/L252P or TSHR/C41S heterodimers could only bind one TSH, TSH-stimulated IP1 production was decreased relative to cAMP production. The slopes of linear regression analyses comparing fold stimulation by TSH of IP1 vs. cAMP production were 0.044 ± 0.0047, 0.0043 ± 0.0041, and 0.0059 ± 0.0014 for cells expressing TSHR alone, TSHR and L252P, or TSHR and C41S, respectively. We suggest that TSHR coupling to phosphoinositide signaling is dependent on binding 2 molecules of TSH to TSHR homodimer, causing a conformational change allowing coupling to G(q/11).
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Affiliation(s)
- Michael D Allen
- Clinical Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-8029, USA
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Vilar S, Ferino G, Phatak SS, Berk B, Cavasotto CN, Costanzi S. Docking-based virtual screening for ligands of G protein-coupled receptors: not only crystal structures but also in silico models. J Mol Graph Model 2010; 29:614-23. [PMID: 21146435 DOI: 10.1016/j.jmgm.2010.11.005] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2010] [Revised: 10/28/2010] [Accepted: 11/09/2010] [Indexed: 12/21/2022]
Abstract
G protein-coupled receptors (GPCRs) regulate a wide range of physiological functions and hold great pharmaceutical interest. Using the β(2)-adrenergic receptor as a case study, this article explores the applicability of docking-based virtual screening to the discovery of GPCR ligands and defines methods intended to improve the screening performance. Our controlled computational experiments were performed on a compound dataset containing known agonists and blockers of the receptor as well as a large number of decoys. The screening based on the structure of the receptor crystallized in complex with its inverse agonist carazolol yielded excellent results, with a clearly delineated prioritization of ligands over decoys. Blockers generally were preferred over agonists; however, agonists were also well distinguished from decoys. A method was devised to increase the screening yields by generating an ensemble of alternative conformations of the receptor that accounts for its flexibility. Moreover, a method was devised to improve the retrieval of agonists, based on the optimization of the receptor around a known agonist. Finally, the applicability of docking-based virtual screening also to homology models endowed with different levels of accuracy was proved. This last point is of uttermost importance, since crystal structures are available only for a limited number of GPCRs, and extends our conclusions to the entire superfamily. The outcome of this analysis definitely supports the application of computer-aided techniques to the discovery of novel GPCR ligands, especially in light of the fact that, in the near future, experimental structures are expected to be solved and become available for an ever increasing number of GPCRs.
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Affiliation(s)
- Santiago Vilar
- Laboratory of Biological Modeling, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, DHHS, Bethesda, MD 20892, USA
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Wallis M. Molecular evolution of the thyrotrophin-releasing hormone precursor in vertebrates: insights from comparative genomics. J Neuroendocrinol 2010; 22:608-19. [PMID: 20298454 DOI: 10.1111/j.1365-2826.2010.01996.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Human preprothyrotrophin-releasing hormone (ppTRH) includes six copies of the TRH sequence, the rat and mouse precursors have five, and those of non-mammalian vertebrates have up to eight. In the present study, the evolutionary basis of this variation was investigated using ppTRH gene sequences extracted from available vertebrate genomic databases. A structure based on eight TRH repeats appears to be the norm for non-mammalian vertebrates, but in all mammals except monotremes this number is reduced to a maximum of six. In some species, one (or more) of the TRH repeats has been mutated, probably rendering it functionless and, in a few species, one or two copies of the TRH sequence have been deleted completely. Sequences of regions between the TRH sequences are poorly conserved, despite reports that several active peptides are produced from these regions. The 5' untranslated region of ppTRH is also very variable but, in eutherians, the promoter region immediately upstream of the gene is quite strongly conserved. In particular, those sequences identified as being involved in transcriptional regulation are well conserved in most eutherians, although they are largely absent from other vertebrates. In most species, gene order around the ppTRH locus is conserved, although exceptions include man and chimpanzee, as well as rat and mouse. The comparative genomics approach thus provides a wider view than previously available of the range of ppTRH genes in vertebrates, and of the species specificity displayed by this molecule.
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Affiliation(s)
- M Wallis
- Biochemistry Department, School of Life Sciences, University of Sussex, Brighton, UK.
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Kleinau G, Haas AK, Neumann S, Worth CL, Hoyer I, Furkert J, Rutz C, Gershengorn MC, Schülein R, Krause G. Signaling-sensitive amino acids surround the allosteric ligand binding site of the thyrotropin receptor. FASEB J 2010; 24:2347-54. [PMID: 20179143 DOI: 10.1096/fj.09-149146] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The thyrotropin receptor [thyroid-stimulating hormone receptor (TSHR)], a G-protein-coupled receptor (GPCR), is endogenously activated by thyrotropin, which binds to the extracellular region of the receptor. We previously identified a low-molecular-weight (LMW) agonist of the TSHR and predicted its allosteric binding pocket within the receptor's transmembrane domain. Because binding of the LMW agonist probably disrupts interactions or leads to formation of new interactions among amino acid residues surrounding the pocket, we tested whether mutation of residues at these positions would lead to constitutive signaling activity. Guided by molecular modeling, we performed site-directed mutagenesis of 24 amino acids in this spatial region, followed by functional characterization of the mutant receptors in terms of expression and signaling, measured as cAMP accumulation. We found that mutations V421I, Y466A, T501A, L587V, M637C, M637W, S641A, Y643F, L645V, and Y667A located in several helices exhibit constitutive activity. Of note is mutation M637W at position 6.48 in transmembrane helix 6, which has a significant effect on the interaction of the receptor with the LMW agonist. In summary, we found that a high proportion of residues in several helices surrounding the allosteric binding site of LMW ligands in the TSHR when mutated lead to constitutively active receptors. Our findings of signaling-sensitive residues in this region of the transmembrane bundle may be of general importance as this domain appears to be evolutionarily retained among GPCRs.
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Affiliation(s)
- Gunnar Kleinau
- Leibniz-Institut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, D-13125 Berlin, Germany
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Neumann S, Raaka BM, Gershengorn MC. Constitutively active thyrotropin and thyrotropin-releasing hormone receptors and their inverse agonists. Methods Enzymol 2010; 485:147-60. [PMID: 21050916 PMCID: PMC6284803 DOI: 10.1016/b978-0-12-381296-4.00009-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Receptors for thyrotropin-releasing hormone (TRH) and thyrotropin (thyroid-stimulating hormone-TSH) are important regulators of the function of the TSH-producing cells of the anterior pituitary gland and the thyroid gland, respectively, and thereby play a central role in thyroid hormone homeostasis. Although the roles of TRH- and TSH-stimulated signaling in these endocrine glands are well understood, these receptors are expressed in other sites and their roles in these extraglandular tissues are less well known. Moreover, one of the two subtypes of TRH receptors (TRH-R2) and the single TSH receptor (TSHR) exhibit constitutive signaling activity and the roles of constitutive signaling by these receptors are poorly understood. One approach to studying constitutive signaling is to use inverse agonists. In this chapter, we will describe the experimental procedures used to measure constitutive signaling by TRH-R2 and TSHR and the effects of their specific inverse agonists.
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Affiliation(s)
- Susanne Neumann
- Clinical Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA
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Comparative sequence and structural analyses of G-protein-coupled receptor crystal structures and implications for molecular models. PLoS One 2009; 4:e7011. [PMID: 19756152 PMCID: PMC2738427 DOI: 10.1371/journal.pone.0007011] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2009] [Accepted: 08/10/2009] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Up until recently the only available experimental (high resolution) structure of a G-protein-coupled receptor (GPCR) was that of bovine rhodopsin. In the past few years the determination of GPCR structures has accelerated with three new receptors, as well as squid rhodopsin, being successfully crystallized. All share a common molecular architecture of seven transmembrane helices and can therefore serve as templates for building molecular models of homologous GPCRs. However, despite the common general architecture of these structures key differences do exist between them. The choice of which experimental GPCR structure(s) to use for building a comparative model of a particular GPCR is unclear and without detailed structural and sequence analyses, could be arbitrary. The aim of this study is therefore to perform a systematic and detailed analysis of sequence-structure relationships of known GPCR structures. METHODOLOGY We analyzed in detail conserved and unique sequence motifs and structural features in experimentally-determined GPCR structures. Deeper insight into specific and important structural features of GPCRs as well as valuable information for template selection has been gained. Using key features a workflow has been formulated for identifying the most appropriate template(s) for building homology models of GPCRs of unknown structure. This workflow was applied to a set of 14 human family A GPCRs suggesting for each the most appropriate template(s) for building a comparative molecular model. CONCLUSIONS The available crystal structures represent only a subset of all possible structural variation in family A GPCRs. Some GPCRs have structural features that are distributed over different crystal structures or which are not present in the templates suggesting that homology models should be built using multiple templates. This study provides a systematic analysis of GPCR crystal structures and a consistent method for identifying suitable templates for GPCR homology modelling that will help to produce more reliable three-dimensional models.
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Kleinau G, Krause G. Thyrotropin and homologous glycoprotein hormone receptors: structural and functional aspects of extracellular signaling mechanisms. Endocr Rev 2009; 30:133-51. [PMID: 19176466 DOI: 10.1210/er.2008-0044] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The TSH receptor (TSHR) together with the homologous lutropin/choriogonadotropin receptor and the follitropin receptor are glycoprotein hormone receptors (GPHRs). They constitute a subfamily of the rhodopsin-like G protein-coupled receptors with seven transmembrane helices. GPHRs and their corresponding hormones are pivotal proteins with respect to a variety of physiological functions. The identification and characterization of intra- and intermolecular signaling determinants as well as signaling mechanisms are prerequisites to gaining molecular insights into functions and (pathogenic) dysfunctions of GPHRs. Knowledge about activation mechanisms is fragmentary, and the specific aspects have still not been understood in their entirety. Therefore, here we critically review the data available for these receptors and bring together structural and functional findings with a focus on the important large extracellular portion of the TSHR. One main focus is the particular function of structural determinants in the initial steps of the activation such as: 1) hormone binding at the extracellular site; 2) hormone interaction at a second binding site in the hinge region; 3) signal regulation via sequence motifs in the hinge region; and 4) synergistic signal amplification by cooperative effects of the extracellular loops toward the transmembrane region. Comparison and consolidation of data from the homologous glycoprotein hormone receptors TSHR, follitropin receptor, and lutropin/choriogonadotropin receptor provide an overview of extracellular mechanisms of signal initiation, conduction, and regulation at the TSHR and homologous receptors. Finally, we address the issue of structural implications and suggest a refined scenario for the initial signaling process on GPHRs.
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Affiliation(s)
- Gunnar Kleinau
- Leibniz-Institut für Molekulare Pharmakologie, Berlin, Germany
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Parravicini C, Ranghino G, Abbracchio MP, Fantucci P. GPR17: molecular modeling and dynamics studies of the 3-D structure and purinergic ligand binding features in comparison with P2Y receptors. BMC Bioinformatics 2008; 9:263. [PMID: 18533035 PMCID: PMC2443813 DOI: 10.1186/1471-2105-9-263] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2007] [Accepted: 06/04/2008] [Indexed: 02/06/2023] Open
Abstract
Background GPR17 is a G-protein-coupled receptor located at intermediate phylogenetic position between two distinct receptor families: the P2Y and CysLT receptors for extracellular nucleotides and cysteinyl-LTs, respectively. We previously showed that GPR17 can indeed respond to both classes of endogenous ligands and to synthetic compounds active at the above receptor families, thus representing the first fully characterized non-peptide "hybrid" GPCR. In a rat brain focal ischemia model, the selective in vivo knock down of GPR17 by anti-sense technology or P2Y/CysLT antagonists reduced progression of ischemic damage, thus highlighting GPR17 as a novel therapeutic target for stroke. Elucidation of the structure of GPR17 and of ligand binding mechanisms are the necessary steps to obtain selective and potent drugs for this new potential target. On this basis, a 3-D molecular model of GPR17 embedded in a solvated phospholipid bilayer and refined by molecular dynamics simulations has been the first aim of this study. To explore the binding mode of the "purinergic" component of the receptor, the endogenous agonist UDP and two P2Y receptor antagonists demonstrated to be active on GPR17 (MRS2179 and cangrelor) were then modeled on the receptor. Results Molecular dynamics simulations suggest that GPR17 nucleotide binding pocket is similar to that described for the other P2Y receptors, although only one of the three basic residues that have been typically involved in ligand recognition is conserved (Arg255). The binding pocket is enclosed between the helical bundle and covered at the top by EL2. Driving interactions are H-bonds and salt bridges between the 6.55 and 6.52 residues and the phosphate moieties of the ligands. An "accessory" binding site in a region formed by the EL2, EL3 and the Nt was also found. Conclusion Nucleotide binding to GPR17 occurs on the same receptor regions identified for already known P2Y receptors. Agonist/antagonist binding mode are similar, but not identical. An accessory external binding site could guide small ligands to the deeper principal binding site in a multi-step mechanism of activation. The nucleotide binding pocket appears to be unable to allocate the leukotrienic type ligands in the same effective way.
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Affiliation(s)
- Chiara Parravicini
- Laboratory of Cellular and Molecular Pharmacology of Purinergic Transmission, Department of Pharmacological Sciences, University of Milan, Via Balzaretti 9, 20133 Milan, Italy.
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