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Ordaz RP, Garay E, Limon A, Pérez-Samartín A, Sánchez-Gómez MV, Robles-Martínez L, Cisneros-Mejorado A, Matute C, Arellano RO. GABA A Receptors Expressed in Oligodendrocytes Cultured from the Neonatal Rat Contain α3 and γ1 Subunits and Present Differential Functional and Pharmacological Properties. Mol Pharmacol 2020; 99:133-146. [PMID: 33288547 DOI: 10.1124/molpharm.120.000091] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Accepted: 11/05/2020] [Indexed: 12/25/2022] Open
Abstract
Oligodendrocytes (OLs) express functional GABAA receptors (GABAARs) that are activated by GABA released at synaptic contacts with axons or by ambient GABA in extrasynaptic domains. In both instances, the receptors' molecular identity has not been fully defined. Furthermore, data on their structural diversity in different brain regions and information on age-dependent changes in their molecular composition are scant. This lack of knowledge has delayed access to a better understanding of the role of GABAergic signaling between neurons and OLs. Here, we used functional, and pharmacological analyses, as well as gene and protein expression of GABAAR subunits, to explore the subunit combination that could explain the receptor functional profile expressed in OLs from the neonate rat. We found that GABAAR composed of α3β2γ1 subunits mimicked the characteristics of the endogenous receptor when expressed heterologously in Xenopus laevis oocytes. Either α3 or γ1 subunit silencing by small interfering RNA transfection changed the GABA-response characteristics in oligodendrocyte precursor cells, indicating their participation in the endogenous receptor conformation. Thus, α3 subunit silencing shifted the mean EC50 for GABA from 75.1 to 46.6 µM, whereas γ1 silencing reduced the current amplitude response by 55%. We also observed that β-carbolines differentially enhance GABA responses in oligodendroglia as compared with those in neurons. These results contribute to defining the molecular and pharmacological properties of GABAARs in OLs. Additionally, the identification of β-carbolines as selective enhancers of GABAARs in OLs may help to study the role of GABAergic signaling during myelination. SIGNIFICANCE STATEMENT: GABAergic signaling through GABAA receptors (GABAARs) expressed in the oligodendroglial lineage contributes to the myelination control. Determining the molecular identity and the pharmacology of these receptors is essential to define their specific roles in myelination. Using GABAAR subunit expression and silencing, we identified that the GABAAR subunit combination α3β2γ1 conforms the bulk of GABAARs in oligodendrocytes from rat neonates. Furthermore, we found that these receptors have differential pharmacological properties that allow specific positive modulation by β-carbolines.
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Affiliation(s)
- Rainald Pablo Ordaz
- Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.P.O., E.G., L.R.-M., A.C.-M., R.O.A.); Mitchell Center for Neurodegenerative Diseases, Department of Neurology, School of Medicine, University of Texas Medical Branch at Galveston, Galveston, Texas (A.L.); and Achucarro Basque Center for Neuroscience, CIBERNED and Departamento de Neurociencias, Universidad del País Vasco (UPV/EHU), Leioa, Spain (A.P.-S., M.V.S.-G., C.M.)
| | - Edith Garay
- Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.P.O., E.G., L.R.-M., A.C.-M., R.O.A.); Mitchell Center for Neurodegenerative Diseases, Department of Neurology, School of Medicine, University of Texas Medical Branch at Galveston, Galveston, Texas (A.L.); and Achucarro Basque Center for Neuroscience, CIBERNED and Departamento de Neurociencias, Universidad del País Vasco (UPV/EHU), Leioa, Spain (A.P.-S., M.V.S.-G., C.M.)
| | - Agenor Limon
- Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.P.O., E.G., L.R.-M., A.C.-M., R.O.A.); Mitchell Center for Neurodegenerative Diseases, Department of Neurology, School of Medicine, University of Texas Medical Branch at Galveston, Galveston, Texas (A.L.); and Achucarro Basque Center for Neuroscience, CIBERNED and Departamento de Neurociencias, Universidad del País Vasco (UPV/EHU), Leioa, Spain (A.P.-S., M.V.S.-G., C.M.)
| | - Alberto Pérez-Samartín
- Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.P.O., E.G., L.R.-M., A.C.-M., R.O.A.); Mitchell Center for Neurodegenerative Diseases, Department of Neurology, School of Medicine, University of Texas Medical Branch at Galveston, Galveston, Texas (A.L.); and Achucarro Basque Center for Neuroscience, CIBERNED and Departamento de Neurociencias, Universidad del País Vasco (UPV/EHU), Leioa, Spain (A.P.-S., M.V.S.-G., C.M.)
| | - María Victoria Sánchez-Gómez
- Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.P.O., E.G., L.R.-M., A.C.-M., R.O.A.); Mitchell Center for Neurodegenerative Diseases, Department of Neurology, School of Medicine, University of Texas Medical Branch at Galveston, Galveston, Texas (A.L.); and Achucarro Basque Center for Neuroscience, CIBERNED and Departamento de Neurociencias, Universidad del País Vasco (UPV/EHU), Leioa, Spain (A.P.-S., M.V.S.-G., C.M.)
| | - Leticia Robles-Martínez
- Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.P.O., E.G., L.R.-M., A.C.-M., R.O.A.); Mitchell Center for Neurodegenerative Diseases, Department of Neurology, School of Medicine, University of Texas Medical Branch at Galveston, Galveston, Texas (A.L.); and Achucarro Basque Center for Neuroscience, CIBERNED and Departamento de Neurociencias, Universidad del País Vasco (UPV/EHU), Leioa, Spain (A.P.-S., M.V.S.-G., C.M.)
| | - Abraham Cisneros-Mejorado
- Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.P.O., E.G., L.R.-M., A.C.-M., R.O.A.); Mitchell Center for Neurodegenerative Diseases, Department of Neurology, School of Medicine, University of Texas Medical Branch at Galveston, Galveston, Texas (A.L.); and Achucarro Basque Center for Neuroscience, CIBERNED and Departamento de Neurociencias, Universidad del País Vasco (UPV/EHU), Leioa, Spain (A.P.-S., M.V.S.-G., C.M.)
| | - Carlos Matute
- Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.P.O., E.G., L.R.-M., A.C.-M., R.O.A.); Mitchell Center for Neurodegenerative Diseases, Department of Neurology, School of Medicine, University of Texas Medical Branch at Galveston, Galveston, Texas (A.L.); and Achucarro Basque Center for Neuroscience, CIBERNED and Departamento de Neurociencias, Universidad del País Vasco (UPV/EHU), Leioa, Spain (A.P.-S., M.V.S.-G., C.M.)
| | - Rogelio O Arellano
- Instituto de Neurobiología, Laboratorio de Neurofisiología Celular, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, México (R.P.O., E.G., L.R.-M., A.C.-M., R.O.A.); Mitchell Center for Neurodegenerative Diseases, Department of Neurology, School of Medicine, University of Texas Medical Branch at Galveston, Galveston, Texas (A.L.); and Achucarro Basque Center for Neuroscience, CIBERNED and Departamento de Neurociencias, Universidad del País Vasco (UPV/EHU), Leioa, Spain (A.P.-S., M.V.S.-G., C.M.)
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Horsman GP, Jirasek A, Vaillancourt FH, Barbosa CJ, Jarzecki AA, Xu C, Mekmouche Y, Spiro TG, Lipscomb JD, Blades MW, Turner RF, Eltis LD. Spectroscopic studies of the anaerobic enzyme-substrate complex of catechol 1,2-dioxygenase. J Am Chem Soc 2006; 127:16882-91. [PMID: 16316234 PMCID: PMC3418915 DOI: 10.1021/ja053800o] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The basis of the respective regiospecificities of intradiol and extradiol dioxygenase is poorly understood and may be linked to the protonation state of the bidentate-bound catechol in the enzyme/substrate complex. Previous ultraviolet resonance Raman (UVRR) and UV-visible (UV-vis) difference spectroscopic studies demonstrated that, in extradiol dioxygenases, the catechol is bound to the Fe(II) as a monoanion. In this study, we use the same approaches to demonstrate that, in catechol 1,2-dioxygenase (C12O), an intradiol enzyme, the catechol binds to the Fe(III) as a dianion. Specifically, features at 290 nm and 1550 cm(-1) in the UV-vis and UVRR difference spectra, respectively, are assigned to dianionic catechol based on spectra of the model compound, ferric tris(catecholate). The UVRR spectroscopic band assignments are corroborated by density functional theory (DFT) calculations. In addition, negative features at 240 nm in UV-vis difference spectra and at 1600, 1210, and 1175 cm(-1) in UVRR difference spectra match those of a tyrosinate model compound, consistent with protonation of the axial tyrosinate ligand when it is displaced from the ferric ion coordination sphere upon substrate binding. The DFT calculations ascribe the asymmetry of the bound dianionic substrate to the trans donor effect of an equatorially ligated tyrosinate ligand. In addition, the computations suggest that trans donation from the tyrosinate ligand may facilitate charge transfer from the substrate to yield the iron-bound semiquinone transition state, which is capable of reacting with dioxygen. In illustrating the importance of ligand trans effects in a biological system, the current study demonstrates the power of combining difference UVRR and optical spectroscopies to probe metal ligation in solution.
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Affiliation(s)
- Geoff P. Horsman
- Departments of Biochemistry and Microbiology, The University of British Columbia, Vancouver, BC, V6T 1Z3, Canada
| | - Andrew Jirasek
- Department of Chemistry, The University of British Columbia, Vancouver, BC, V6T 1Z1, Canada
- Michael Smith Laboratories, The University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Frédéric H. Vaillancourt
- Departments of Biochemistry and Microbiology, The University of British Columbia, Vancouver, BC, V6T 1Z3, Canada
| | - Christopher J. Barbosa
- Department of Chemistry, The University of British Columbia, Vancouver, BC, V6T 1Z1, Canada
- Michael Smith Laboratories, The University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | | | - Changliang Xu
- Department of Chemistry, Princeton University, Princeton, NJ, 08544, USA
| | - Yasmina Mekmouche
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN, 55455, USA
| | - Thomas G. Spiro
- Department of Chemistry, Princeton University, Princeton, NJ, 08544, USA
| | - John D. Lipscomb
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN, 55455, USA
| | - Michael W. Blades
- Department of Chemistry, The University of British Columbia, Vancouver, BC, V6T 1Z1, Canada
| | - Robin F.B. Turner
- Michael Smith Laboratories, The University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
- Department of Electrical and Computer Engineering, The University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Lindsay D. Eltis
- Departments of Biochemistry and Microbiology, The University of British Columbia, Vancouver, BC, V6T 1Z3, Canada
- Corresponding author: Lindsay D. Eltis,
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Vaillancourt FH, Barbosa CJ, Spiro TG, Bolin JT, Blades MW, Turner RFB, Eltis LD. Definitive evidence for monoanionic binding of 2,3-dihydroxybiphenyl to 2,3-dihydroxybiphenyl 1,2-dioxygenase from UV resonance Raman spectroscopy, UV/Vis absorption spectroscopy, and crystallography. J Am Chem Soc 2002; 124:2485-96. [PMID: 11890797 DOI: 10.1021/ja0174682] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ultraviolet resonance Raman spectroscopy (UVRRS), electronic absorption spectroscopy, and X-ray crystallography were used to probe the nature of the binding of 2,3-dihydroxybiphenyl (DHB) to the extradiol ring-cleavage enzyme, 2,3-dihydroxybiphenyl 1,2-dioxygenase (DHBD; EC 1.13.11.39). The lowest lying transitions in the electronic absorption spectrum of DHBD-bound DHB occurred at 299 nm, compared to 305 nm for the monoanionic DHB species in buffer. In contrast, the corresponding transitions in neutral and dianionic DHB occurred at 283 and 348 nm, respectively, indicating that DHBD-bound DHB is monoanionic. These binding-induced spectral changes, and the use of custom-designed optical fiber probes, facilitated UVRR experiments. The strongest feature of the UVRR spectrum of DHB was a Y8a-like mode around 1600 cm(-1), whose position depended strongly on the protonation state of the DHB. In the spectrum of the DHBD-bound species, this feature occurred at 1603 cm(-1), as observed in the spectrum of monoanionic DHB. Raman band shifts were observed in deuterated solvent, ruling out dianionic binding of the substrate. Thus, the electronic absorption and UVRRS data demonstrate that DHBD binds its catecholic substrate as a monoanion, definitively establishing this feature of the proposed mechanism of extradiol dioxygenases. This conclusion is supported by a crystal structure of the DHBD:DHB complex at 2.0 A resolution, which suggests that the substrate's 2-hydroxyl substituent, and not the 3-hydroxyl group, deprotonates upon binding. The structural data also show that the aromatic rings of the enzyme-bound DHB are essentially orthogonal to each other. Thus, the 6 nm blue shift of the transition for bound DHB relative to the monoanion in solution could indicate a conformational change upon binding. Catalytic roles of active site residues are proposed based on the structural data and previously proposed mechanistic schemes.
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Affiliation(s)
- Frédéric H Vaillancourt
- Department of Biochemistry, The University of British Columbia, 300-6174 University Boulevard, Vancouver, B.C., V6T 1Z3, Canada
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