1
|
Nicoli A, Dunkel A, Giorgino T, de Graaf C, Di Pizio A. Classification Model for the Second Extracellular Loop of Class A GPCRs. J Chem Inf Model 2022; 62:511-522. [PMID: 35113559 DOI: 10.1021/acs.jcim.1c01056] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The extracellular loop 2 (ECL2) is the longest and the most diverse loop among class A G protein-coupled receptors (GPCRs). It connects the transmembrane (TM) helices 4 and 5 and contains a highly conserved cysteine through which it is bridged with TM3. In this paper, experimental ECL2 structures were analyzed based on their sequences, shapes, and intramolecular contacts. To take into account the flexibility, we incorporated into our analyses information from the molecular dynamics trajectories available on the GPCRmd website. Despite the high sequence variability, shapes of the analyzed structures, defined by the backbone volume overlaps, can be clustered into seven main groups. Conformational differences within the clusters can be then identified by intramolecular interactions with other GPCR structural domains. Overall, our work provides a reorganization of the structural information of the ECL2 of class A GPCR subfamilies, highlighting differences and similarities on sequence and conformation levels.
Collapse
Affiliation(s)
- Alessandro Nicoli
- Leibniz Institute for Food Systems Biology at the Technical University of Munich, 85354 Freising, Germany
| | - Andreas Dunkel
- Leibniz Institute for Food Systems Biology at the Technical University of Munich, 85354 Freising, Germany
| | - Toni Giorgino
- Biophysics Institute, National Research Council (CNR-IBF), 20133 Milan, Italy
| | - Chris de Graaf
- Sosei Heptares, Steinmetz Building, Granta Park, Great Abington, Cambridge CB21 6DG, U.K
| | - Antonella Di Pizio
- Leibniz Institute for Food Systems Biology at the Technical University of Munich, 85354 Freising, Germany
| |
Collapse
|
2
|
Thermostability-based binding assays reveal complex interplay of cation, substrate and lipid binding in the bacterial DASS transporter, VcINDY. Biochem J 2021; 478:3847-3867. [PMID: 34643224 PMCID: PMC8652582 DOI: 10.1042/bcj20210061] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2021] [Revised: 10/08/2021] [Accepted: 10/13/2021] [Indexed: 12/04/2022]
Abstract
The divalent anion sodium symporter (DASS) family of transporters (SLC13 family in humans) are key regulators of metabolic homeostasis, disruption of which results in protection from diabetes and obesity, and inhibition of liver cancer cell proliferation. Thus, DASS transporter inhibitors are attractive targets in the treatment of chronic, age-related metabolic diseases. The characterisation of several DASS transporters has revealed variation in the substrate selectivity and flexibility in the coupling ion used to power transport. Here, using the model DASS co-transporter, VcINDY from Vibrio cholerae, we have examined the interplay of the three major interactions that occur during transport: the coupling ion, the substrate, and the lipid environment. Using a series of high-throughput thermostability-based interaction assays, we have shown that substrate binding is Na+-dependent; a requirement that is orchestrated through a combination of electrostatic attraction and Na+-induced priming of the binding site architecture. We have identified novel DASS ligands and revealed that ligand binding is dominated by the requirement of two carboxylate groups in the ligand that are precisely distanced to satisfy carboxylate interaction regions of the substrate-binding site. We have also identified a complex relationship between substrate and lipid interactions, which suggests a dynamic, regulatory role for lipids in VcINDY's transport cycle.
Collapse
|
3
|
Nguyen KDQ, Vigers M, Sefah E, Seppälä S, Hoover JP, Schonenbach NS, Mertz B, O'Malley MA, Han S. Homo-oligomerization of the human adenosine A 2A receptor is driven by the intrinsically disordered C-terminus. eLife 2021; 10:e66662. [PMID: 34269678 PMCID: PMC8328514 DOI: 10.7554/elife.66662] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Accepted: 07/15/2021] [Indexed: 11/27/2022] Open
Abstract
G protein-coupled receptors (GPCRs) have long been shown to exist as oligomers with functional properties distinct from those of the monomeric counterparts, but the driving factors of oligomerization remain relatively unexplored. Herein, we focus on the human adenosine A2A receptor (A2AR), a model GPCR that forms oligomers both in vitro and in vivo. Combining experimental and computational approaches, we discover that the intrinsically disordered C-terminus of A2AR drives receptor homo-oligomerization. The formation of A2AR oligomers declines progressively with the shortening of the C-terminus. Multiple interaction types are responsible for A2AR oligomerization, including disulfide linkages, hydrogen bonds, electrostatic interactions, and hydrophobic interactions. These interactions are enhanced by depletion interactions, giving rise to a tunable network of bonds that allow A2AR oligomers to adopt multiple interfaces. This study uncovers the disordered C-terminus as a prominent driving factor for the oligomerization of a GPCR, offering important insight into the effect of C-terminus modification on receptor oligomerization of A2AR and other GPCRs reconstituted in vitro for biophysical studies.
Collapse
Affiliation(s)
- Khanh Dinh Quoc Nguyen
- Department of Chemistry and Biochemistry, University of California, Santa BarbaraSanta BarbaraUnited States
| | - Michael Vigers
- Department of Chemical Engineering, University of California, Santa BarbaraSanta BarbaraUnited States
| | - Eric Sefah
- C. Eugene Bennett Department of Chemistry, West Virginia UniversityMorgantownUnited States
| | - Susanna Seppälä
- Department of Chemical Engineering, University of California, Santa BarbaraSanta BarbaraUnited States
| | - Jennifer Paige Hoover
- Department of Chemistry and Biochemistry, University of California, Santa BarbaraSanta BarbaraUnited States
| | - Nicole Star Schonenbach
- Department of Chemical Engineering, University of California, Santa BarbaraSanta BarbaraUnited States
| | - Blake Mertz
- C. Eugene Bennett Department of Chemistry, West Virginia UniversityMorgantownUnited States
| | - Michelle Ann O'Malley
- Department of Chemical Engineering, University of California, Santa BarbaraSanta BarbaraUnited States
| | - Songi Han
- Department of Chemistry and Biochemistry, University of California, Santa BarbaraSanta BarbaraUnited States
- Department of Chemical Engineering, University of California, Santa BarbaraSanta BarbaraUnited States
| |
Collapse
|
4
|
Deshpande CN, Azucenas CR, Qiao B, Nomura N, Xin V, Font J, Iwata S, Ganz T, Nemeth E, Mackenzie B, Jormakka M. Isolation and thermal stabilization of mouse ferroportin. FEBS Open Bio 2020; 11:26-34. [PMID: 33190422 PMCID: PMC7780100 DOI: 10.1002/2211-5463.13039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Revised: 10/30/2020] [Accepted: 11/12/2020] [Indexed: 12/03/2022] Open
Abstract
Ferroportin (Fpn) is an essential mammalian iron transporter that is negatively regulated by the hormone hepcidin. Our current molecular understanding of Fpn‐mediated iron efflux and regulation is limited due to a lack of biochemical, biophysical and high‐resolution structural studies. A critical step towards understanding the transport mechanism of Fpn is to obtain sufficient quantities of pure and stable protein for downstream studies. As such, we detail here an expression and purification protocol for mouse Fpn yielding milligram quantities of pure protein. We have generated deletion constructs exhibiting enhanced thermal stability and which retained iron‐transport activity and hepcidin responsiveness, providing a platform for further biophysical studies of Fpn.
Collapse
Affiliation(s)
| | - Corbin R Azucenas
- Department of Pharmacology & Systems Physiology, University of Cincinnati College of Medicine, OH.,Medical Sciences Baccalaureate Program, University of Cincinnati College of Medicine, OH, USA
| | - Bo Qiao
- Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Norimichi Nomura
- Department of Cell Biology, Graduate School of Medicine, Kyoto University, Japan
| | - Vicky Xin
- Structural Biology Program, Centenary Institute, Sydney, NSW, Australia
| | - Josep Font
- Structural Biology Program, Centenary Institute, Sydney, NSW, Australia
| | - So Iwata
- Department of Cell Biology, Graduate School of Medicine, Kyoto University, Japan
| | - Tomas Ganz
- Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA, USA.,Department of Pathology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Elizabeta Nemeth
- Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Bryan Mackenzie
- Medical Sciences Baccalaureate Program, University of Cincinnati College of Medicine, OH, USA.,Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Mika Jormakka
- Structural Biology Program, Centenary Institute, Sydney, NSW, Australia
| |
Collapse
|
5
|
Schonenbach NS, Rieth MD, Han S, O'Malley MA. Adenosine A2a receptors form distinct oligomers in protein detergent complexes. FEBS Lett 2016; 590:3295-306. [PMID: 27543907 DOI: 10.1002/1873-3468.12367] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2016] [Revised: 08/10/2016] [Accepted: 08/15/2016] [Indexed: 12/12/2022]
Abstract
The human adenosine A2a receptor (A2aR) tunes its function by forming homo-oligomers and hetero-oligomers with other G protein-coupled receptors, but the biophysical characterization of these oligomeric species is limited. Here, we show that upon reconstitution into an optimized mixed micelle system, and purification via an antagonist affinity column, full-length A2aR exists as a distribution of oligomers. We isolated the dimer population from the other oligomers via size exclusion chromatography and showed that it is stable upon dilution, thus supporting the hypotheses that the A2aR dimer has a defined structure and function. This study presents a crucial enabling step to a detailed biophysical characterization of A2aR homodimers.
Collapse
Affiliation(s)
- Nicole S Schonenbach
- Department of Chemical Engineering, University of California Santa Barbara, CA, USA
| | - Monica D Rieth
- Department of Chemical Engineering, University of California Santa Barbara, CA, USA
| | - Songi Han
- Department of Chemical Engineering, University of California Santa Barbara, CA, USA.,Department of Chemistry and Biochemistry, University of California Santa Barbara, CA, USA
| | - Michelle A O'Malley
- Department of Chemical Engineering, University of California Santa Barbara, CA, USA.
| |
Collapse
|
6
|
Naranjo AN, McNeely PM, Katsaras J, Robinson AS. Impact of purification conditions and history on A2A adenosine receptor activity: The role of CHAPS and lipids. Protein Expr Purif 2016; 124:62-7. [PMID: 27241126 DOI: 10.1016/j.pep.2016.05.015] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2016] [Revised: 05/23/2016] [Accepted: 05/26/2016] [Indexed: 02/08/2023]
Abstract
The adenosine A2A receptor (A2AR) is a much-studied class A G protein-coupled receptor (GPCR). For biophysical studies, A2AR is commonly purified in a detergent mixture of dodecylmaltoside (DDM), 3-(3-cholamidopropyl) dimethylammoniopropane sulfonate (CHAPS), and cholesteryl hemisuccinate (CHS). Here we studied the effects of CHAPS on the ligand binding activity and stability of wild type, full-length human A2AR. We also tested the cholesterol requirement for maintaining the active conformation of the receptor when solubilized in detergent micelles. To this end, the receptor was purified using DDM, DDM/CHAPS, or the short hydrocarbon chain lipid 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC, di-6:0PC). After solubilization in DDM, DDM/CHAPS, or DHPC micelles, although A2AR was found to retain its native-like fold, its binding ability was significantly compromised compared to DDM or DDM/CHAPS with CHS. It therefore appears that although cholesterol is not needed for A2AR to retain a native-like, α-helical conformation, it may be a critical component for high affinity ligand binding. Further, this result suggests that the conformational differences between the active and inactive protein may be so subtle that commonly used spectroscopic methods are unable to differentiate between the two forms, highlighting the need for activity measurements. The studies presented in this paper also underline the importance of the protein's purification history; i.e., detergents that interact with the protein during purification affect the ligand binding properties of the receptor in an irreversible manner.
Collapse
Affiliation(s)
- Andrea N Naranjo
- Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19711, United States
| | - Patrick M McNeely
- Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19711, United States
| | - John Katsaras
- Biology and Soft Matter Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6100, United States; Department of Physics and Astronomy, The University of Tennessee, Knoxville, TN 37996-1200, United States; Joint Institute for Neutron Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6453, United States
| | - Anne Skaja Robinson
- Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19711, United States; Department of Chemical and Biomolecular Engineering, 300 Lindy Boggs Laboratory, Tulane University, New Orleans, LA 70118, United States.
| |
Collapse
|
7
|
De Filippo E, Namasivayam V, Zappe L, El-Tayeb A, Schiedel AC, Müller CE. Role of extracellular cysteine residues in the adenosine A2A receptor. Purinergic Signal 2016; 12:313-29. [PMID: 26969588 DOI: 10.1007/s11302-016-9506-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 02/29/2016] [Indexed: 12/13/2022] Open
Abstract
The G protein-coupled A2A adenosine receptor represents an important drug target. Crystal structures and modeling studies indicated that three disulfide bonds are formed between ECL1 and ECL2 (I, Cys71(2.69)-Cys159(45.43); II, Cys74(3.22)-Cys146(45.30), and III, Cys77(3.25)-Cys166(45.50)). However, the A2BAR subtype appears to require only disulfide bond III for proper function. In this study, each of the three disulfide bonds in the A2AAR was disrupted by mutation of one of the cysteine residues to serine. The mutant receptors were stably expressed in Chinese hamster ovary cells and analyzed in cyclic adenosine monophosphate (cAMP) accumulation and radioligand binding studies using structurally diverse agonists: adenosine, NECA, CGS21680, and PSB-15826. Results were rationalized by molecular modeling. The observed effects were dependent on the investigated agonist. Loss of disulfide bond I led to a widening of the orthosteric binding pocket resulting in a strong reduction in the potency of adenosine, but not of NECA or 2-substituted nucleosides. Disruption of disulfide bond II led to a significant reduction in the agonists' efficacy indicating its importance for receptor activation. Disulfide bond III disruption reduced potency and affinity of the small adenosine agonists and NECA, but not of the larger 2-substituted agonists. While all the three disulfide bonds were essential for high potency or efficacy of adenosine, structural modification of the nucleoside could rescue affinity or efficacy at the mutant receptors. At present, it cannot be excluded that formation of the extracellular disulfide bonds in the A2AAR is dynamic. This might add another level of G protein-coupled receptor (GPCR) modulation, in particular for the cysteine-rich A2A and A2BARs.
Collapse
Affiliation(s)
- Elisabetta De Filippo
- Pharma Center Bonn, Pharmaceutical Institute, Pharmaceutical Chemistry I, University of Bonn, An der Immenburg 4, 53121, Bonn, Germany
| | - Vigneshwaran Namasivayam
- Pharma Center Bonn, Pharmaceutical Institute, Pharmaceutical Chemistry I, University of Bonn, An der Immenburg 4, 53121, Bonn, Germany
| | - Lukas Zappe
- Pharma Center Bonn, Pharmaceutical Institute, Pharmaceutical Chemistry I, University of Bonn, An der Immenburg 4, 53121, Bonn, Germany
| | - Ali El-Tayeb
- Pharma Center Bonn, Pharmaceutical Institute, Pharmaceutical Chemistry I, University of Bonn, An der Immenburg 4, 53121, Bonn, Germany
| | - Anke C Schiedel
- Pharma Center Bonn, Pharmaceutical Institute, Pharmaceutical Chemistry I, University of Bonn, An der Immenburg 4, 53121, Bonn, Germany
| | - Christa E Müller
- Pharma Center Bonn, Pharmaceutical Institute, Pharmaceutical Chemistry I, University of Bonn, An der Immenburg 4, 53121, Bonn, Germany.
| |
Collapse
|
8
|
Wang Z, Ye C, Zhang X, Wei Y. Cysteine residue is not essential for CPM protein thermal-stability assay. Anal Bioanal Chem 2015; 407:3683-91. [PMID: 25772562 DOI: 10.1007/s00216-015-8587-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Revised: 02/10/2015] [Accepted: 02/20/2015] [Indexed: 11/29/2022]
Abstract
A popular thermal-stability assay developed especially for the study of membrane proteins uses a thiol-specific probe, 7-diethylamino-3-(4-maleimidophenyl)-4-methylcoumarin (CPM). The fluorescence emission of CPM surges when it forms a covalent bond with the side chain of a free Cys, which becomes more readily accessible upon protein thermal denaturation. Interestingly, the melting temperatures of membrane proteins determined using the CPM assay in literature are closely clustered in the temperature range 45-55 °C. A thorough understanding of the mechanism behind the observed signal change is critical for the accurate interpretation of the protein unfolding. Here we used two α-helical membrane proteins, AqpZ and AcrB, as model systems to investigate the nature of the fluorescence surge in the CPM assay. We found that the transition temperatures measured using circular-dichroism (CD) spectroscopy and the CPM assay were significantly different. To eliminate potential artifact that might arise from the presence of detergent, we monitored the unfolding of two soluble proteins. We found that, contrary to current understanding, the presence of a sulfhydryl group was not a prerequisite for the CPM thermal-stability assay. The observed fluorescence increase is probably caused by binding of the fluorophore to hydrophobic patches exposed upon protein unfolding.
Collapse
Affiliation(s)
- Zhaoshuai Wang
- Department of Chemistry, University of Kentucky, 305 Chemistry-Physics Building, Lexington, KY, 40506, USA
| | | | | | | |
Collapse
|
9
|
Naranjo AN, Chevalier A, Cousins GD, Ayettey E, McCusker EC, Wenk C, Robinson AS. Conserved disulfide bond is not essential for the adenosine A2A receptor: Extracellular cysteines influence receptor distribution within the cell and ligand-binding recognition. BIOCHIMICA ET BIOPHYSICA ACTA 2015; 1848:603-14. [PMID: 25445670 PMCID: PMC4565196 DOI: 10.1016/j.bbamem.2014.11.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2014] [Revised: 10/22/2014] [Accepted: 11/10/2014] [Indexed: 11/16/2022]
Abstract
G protein-coupled receptors (GPCRs) are integral membrane proteins involved in cellular signaling and constitute major drug targets. Despite their importance, the relationship between structure and function of these receptors is not well understood. In this study, the role of extracellular disulfide bonds on the trafficking and ligand-binding activity of the human A2A adenosine receptor was examined. To this end, cysteine-to-alanine mutations were conducted to replace individual and both cysteines in three disulfide bonds present in the first two extracellular loops. Although none of the disulfide bonds were essential for the formation of plasma membrane-localized active GPCR, loss of the disulfide bonds led to changes in the distribution of the receptor within the cell and changes in the ligand-binding affinity. These results indicate that in contrast to many class A GPCRs, the extracellular disulfide bonds of the A2A receptor are not essential, but can modulate the ligand-binding activity, by either changing the conformation of the extracellular loops or perturbing the interactions of the transmembrane domains.
Collapse
Affiliation(s)
- Andrea N Naranjo
- Department of Chemical and Biomolecular Engineering, University of Delaware, 150 Academy Street, Newark, DE 19716, USA.
| | - Amy Chevalier
- Department of Chemical and Biomolecular Engineering, University of Delaware, 150 Academy Street, Newark, DE 19716, USA.
| | - Gregory D Cousins
- Department of Computer Science, Tulane University, 6823 St. Charles Ave, New Orleans, LA 70118, USA
| | - Esther Ayettey
- Department of Chemical and Biomolecular Engineering, University of Delaware, 150 Academy Street, Newark, DE 19716, USA
| | - Emily C McCusker
- Department of Chemical and Biomolecular Engineering, University of Delaware, 150 Academy Street, Newark, DE 19716, USA.
| | - Carola Wenk
- Department of Computer Science, Tulane University, 6823 St. Charles Ave, New Orleans, LA 70118, USA.
| | - Anne S Robinson
- Department of Chemical and Biomolecular Engineering, Tulane University, 300 Lindy Boggs Laboratory, 6823 St. Charles Ave, New Orleans, LA 70118, USA; Department of Chemical and Biomolecular Engineering, University of Delaware, 150 Academy Street, Newark, DE 19716, USA.
| |
Collapse
|
10
|
Blocker KM, Britton ZT, Naranjo AN, McNeely PM, Young CL, Robinson AS. Recombinant G Protein-Coupled Receptor Expression in Saccharomyces cerevisiae for Protein Characterization. Methods Enzymol 2015; 556:165-83. [DOI: 10.1016/bs.mie.2014.12.025] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
|
11
|
Schonenbach NS, Hussain S, O'Malley MA. Structure and function of G protein‐coupled receptor oligomers: implications for drug discovery. WILEY INTERDISCIPLINARY REVIEWS-NANOMEDICINE AND NANOBIOTECHNOLOGY 2014; 7:408-27. [DOI: 10.1002/wnan.1319] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Revised: 09/26/2014] [Accepted: 10/11/2014] [Indexed: 12/21/2022]
Affiliation(s)
- Nicole S. Schonenbach
- Department of Chemical EngineeringUniversity of California Santa BarbaraSanta BarbaraCAUSA
| | - Sunyia Hussain
- Department of Chemical EngineeringUniversity of California Santa BarbaraSanta BarbaraCAUSA
| | - Michelle A. O'Malley
- Department of Chemical EngineeringUniversity of California Santa BarbaraSanta BarbaraCAUSA
| |
Collapse
|
12
|
Tol MB, Deluz C, Hassaine G, Graff A, Stahlberg H, Vogel H. Thermal unfolding of a mammalian pentameric ligand-gated ion channel proceeds at consecutive, distinct steps. J Biol Chem 2012; 288:5756-69. [PMID: 23275379 DOI: 10.1074/jbc.m112.422287] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Pentameric ligand-gated ion channels (LGICs) play an important role in fast synaptic signal transduction. Binding of agonists to the β-sheet-structured extracellular domain opens an ion channel in the transmembrane α-helical region of the LGIC. How the structurally distinct and distant domains are functionally coupled for such central transmembrane signaling processes remains an open question. To obtain detailed information about the stability of and the coupling between these different functional domains, we analyzed the thermal unfolding of a homopentameric LGIC, the 5-hydroxytryptamine receptor (ligand binding, secondary structure, accessibility of Trp and Cys residues, and aggregation), in plasma membranes as well as during detergent extraction, purification, and reconstitution into artificial lipid bilayers. We found a large loss in thermostability correlating with the loss of the lipid bilayer during membrane solubilization and purification. Thermal unfolding of the 5-hydroxytryptamine receptor occurred in consecutive steps at distinct protein locations. A loss of ligand binding was detected first, followed by formation of different transient low oligomeric states of receptor pentamers, followed by partial unfolding of helical parts of the protein, which finally lead to the formation receptor aggregates. Structural destabilization of the receptor in detergents could be partially reversed by reconstituting the receptor into lipid bilayers. Our results are important because they quantify the stability of LGICs during detergent extraction and purification and can be used to create stabilized receptor proteins for structural and functional studies.
Collapse
Affiliation(s)
- Menno B Tol
- Laboratory of Physical Chemistry of Polymers and Membranes, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
| | | | | | | | | | | |
Collapse
|
13
|
Britton ZT, Hanle EI, Robinson AS. An expression and purification system for the biosynthesis of adenosine receptor peptides for biophysical and structural characterization. Protein Expr Purif 2012; 84:224-35. [PMID: 22722102 PMCID: PMC3572917 DOI: 10.1016/j.pep.2012.06.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2012] [Revised: 05/29/2012] [Accepted: 06/08/2012] [Indexed: 11/15/2022]
Abstract
Biophysical and structural characterization of G protein-coupled receptors (GPCRs) has been limited due to difficulties in expression, purification, and vitro stability of the full-length receptors. "Divide and conquer" approaches aimed at the NMR characterization of peptides corresponding to specific regions of the receptor have yielded insights into the structure and dynamics of GPCR activation and signaling. Though significant progress has been made in the generation of peptides that are composed of GPCR transmembrane domains, current methods utilize fusion protein strategies that require chemical cleavage and peptide separation via chromatographic means. We have developed an expression and purification system based on fusion to ketosteroid isomerase, thrombin cleavage, and tandem affinity chromatography that enables the solubilization, cleavage, and characterization in a single detergent system relevant for biophysical and structural characterization. We have applied this expression and purification system to the production and characterization of peptides of the adenosine receptor family of GPCRs in Escherichia coli. Herein, we demonstrate using a model peptide that includes extracellular loop 3, transmembrane domain 7, and a portion of the carboxy-terminus of the adenosine A(2)a receptor that the peptide is sufficiently pure for biophysical characterization, where it adopts α-helical structure. Furthermore, we demonstrate the utility of this system by optimizing the construct for thrombin processing and apply the system to peptides with more complex structures.
Collapse
Affiliation(s)
- Zachary T. Britton
- Department of Chemical and Biomolecular Engineering, University of Delaware, 150 Academy Street, Newark, DE 19716, United States
| | - Elizabeth I. Hanle
- Department of Chemical and Biomolecular Engineering, University of Delaware, 150 Academy Street, Newark, DE 19716, United States
| | - Anne S. Robinson
- Department of Chemical and Biomolecular Engineering, University of Delaware, 150 Academy Street, Newark, DE 19716, United States
- Department of Chemical and Biomolecular Engineering, 300 Lindy Boggs Laboratory, Tulane University, New Orleans, LA 70118, United States
| |
Collapse
|
14
|
Tosh DK, Deflorian F, Phan K, Gao ZG, Wan TC, Gizewski E, Auchampach JA, Jacobson KA. Structure-guided design of A(3) adenosine receptor-selective nucleosides: combination of 2-arylethynyl and bicyclo[3.1.0]hexane substitutions. J Med Chem 2012; 55:4847-60. [PMID: 22559880 PMCID: PMC3371665 DOI: 10.1021/jm300396n] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
(N)-Methanocarba adenosine 5'-methyluronamides containing known A(3) AR (adenosine receptor)-enhancing modifications, i.e., 2-(arylethynyl)adenine and N(6)-methyl or N(6)-(3-substituted-benzyl), were nanomolar full agonists of human (h) A(3)AR and highly selective (K(i) ∼0.6 nM, N(6)-methyl 2-(halophenylethynyl) analogues 13 and 14). Combined 2-arylethynyl-N(6)-3-chlorobenzyl substitutions preserved A(3)AR affinity/selectivity in the (N)-methanocarba series (e.g., 3,4-difluoro full agonist MRS5698 31, K(i) 3 nM, human and mouse A(3)) better than that for ribosides. Polyaromatic 2-ethynyl N(6)-3-chlorobenzyl analogues, such as potent linearly extended 2-p-biphenylethynyl MRS5679 34 (K(i) hA(3) 3.1 nM; A(1), A(2A), inactive) and fluorescent 1-pyrene adduct MRS5704 35 (K(i) hA(3) 68.3 nM), were conformationally rigid; receptor docking identified a large, mainly hydrophobic binding region. The vicinity of receptor-bound C2 groups was probed by homology modeling based on recent X-ray structure of an agonist-bound A(2A)AR, with a predicted helical rearrangement requiring an agonist-specific outward displacement of TM2 resembling opsin. Thus, the X-ray structure of related A(2A)AR is useful in guiding the design of new A(3)AR agonists.
Collapse
Affiliation(s)
- Dilip K. Tosh
- Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892
| | - Francesca Deflorian
- Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892
| | - Khai Phan
- Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892
| | - Zhan-Guo Gao
- Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892
| | - Tina C. Wan
- Department of Pharmacology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226
| | - Elizabeth Gizewski
- Department of Pharmacology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226
| | - John A. Auchampach
- Department of Pharmacology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226
| | - Kenneth A. Jacobson
- Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892
| |
Collapse
|
15
|
Reyes-Alcaraz A, Martínez-Archundia M, Ramon E, Garriga P. Salt effects on the conformational stability of the visual G-protein-coupled receptor rhodopsin. Biophys J 2012; 101:2798-806. [PMID: 22261069 DOI: 10.1016/j.bpj.2011.09.049] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2010] [Revised: 09/21/2011] [Accepted: 09/26/2011] [Indexed: 11/28/2022] Open
Abstract
Membrane protein stability is a key parameter with important physiological and practical implications. Inorganic salts affect protein stability, but the mechanisms of their interactions with membrane proteins are not completely understood. We have undertaken the study of a prototypical G-protein-coupled receptor, the α-helical membrane protein rhodopsin from vertebrate retina, and explored the effects of inorganic salts on the thermal decay properties of both its inactive and photoactivated states. Under high salt concentrations, rhodopsin significantly increased its activation enthalpy change for thermal bleaching, whereas acid denaturation affected the formation of a denatured loose-bundle state for both the active and inactive conformations. This behavior seems to correlate with changes in protonated Schiff-base hydrolysis. However, chromophore regeneration with the 11-cis-retinal chromophore and MetarhodopsinII decay kinetics were slower only in the presence of sodium chloride, suggesting that in this case, the underlying phenomenon may be linked to the activation of rhodopsin and the retinal release processes. Furthermore, the melting temperature, determined by means of circular dichroism and differential scanning calorimetry measurements, was increased in the presence of high salt concentrations. The observed effects on rhodopsin could indicate that salts favor electrostatic interactions in the retinal binding pocket and indirectly favor hydrophobic interactions at the membrane protein receptor core. These effects can be exploited in applications where the stability of membrane proteins in solution is highly desirable.
Collapse
Affiliation(s)
- Arfaxad Reyes-Alcaraz
- Group of Molecular and Industrial Biotechnology, Centre de Biotecnologia Molecular, Departament d'Enginyeria Química, Universitat Politècnica de Catalunya, Terrassa, Catalonia, Spain
| | | | | | | |
Collapse
|
16
|
O'Malley MA, Helgeson ME, Wagner NJ, Robinson AS. Toward rational design of protein detergent complexes: determinants of mixed micelles that are critical for the in vitro stabilization of a G-protein coupled receptor. Biophys J 2012; 101:1938-48. [PMID: 22004748 DOI: 10.1016/j.bpj.2011.09.018] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2011] [Revised: 09/06/2011] [Accepted: 09/12/2011] [Indexed: 01/02/2023] Open
Abstract
Although reconstitution of membrane proteins within protein detergent complexes is often used to enable their structural or biophysical characterization, it is unclear how one should rationally choose the appropriate micellar environment to preserve native protein folding. Here, we investigated model mixed micelles consisting of a nonionic glucosylated alkane surfactant from the maltoside and thiomaltoside families, bile salt surfactant, and the steryl derivative cholesteryl hemisuccinate. We correlated several key attributes of these micelles with the in vitro ligand-binding activity of hA(2)aR in these systems. Through small-angle neutron scattering and radioligand-binding analysis, we found several key aspects of mixed micellar systems that preserve the activity of hA(2)aR, including a critical amount of cholesteryl hemisuccinate per micelle, and an optimal hydrophobic thickness of the micelle that is analogous to the thickness of native mammalian bilayers. These features are closely linked to the headgroup chemistry of the surfactant and the hydrocarbon chain length, which influence both the morphology and composition of resulting micelles. This study should serve as a general guide for selecting the appropriate mixed surfactant systems to stabilize membrane proteins for biophysical analysis.
Collapse
Affiliation(s)
- Michelle A O'Malley
- Department of Chemical Engineering, University of Delaware, Newark, Delaware, USA
| | | | | | | |
Collapse
|
17
|
Yu L, Lu W, Wei Y. AcrB trimer stability and efflux activity, insight from mutagenesis studies. PLoS One 2011; 6:e28390. [PMID: 22163011 PMCID: PMC3230630 DOI: 10.1371/journal.pone.0028390] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2011] [Accepted: 11/07/2011] [Indexed: 11/30/2022] Open
Abstract
The multidrug transporter AcrB in Escherichia coli exists and functions as a homo-trimer. The assembly process of obligate membrane protein oligomers, including AcrB, remains poorly understood. In a previous study, we have shown that individual AcrB subunit is capable of folding independently, suggesting that trimerization of AcrB follows a three-stage pathway in which monomers first fold, and then assemble. Here we destabilized the AcrB trimer through mutating a single Pro (P223) in the protruding loop of AcrB, which drastically reduced the protein activity. We replaced P223 separately with five residues, including Ala, Val, Tyr, Asn, and Gly, and found that AcrBP223G was the least active. Detailed characterization of AcrBP223G revealed that the protein existed as a well-folded monomer after purification, but formed a trimer in vivo. The function of the mutant could be partly restored through strengthening the stability of the trimer using an inter-subunit disulfide bond. Our results also suggested that the protruding loop is well structured during AcrB assembly with P223 served as a “wedge” close to the tip to stabilize the AcrB trimer structure. When this wedge is disrupted, the stability of the trimer is reduced, accompanied by a decrease of drug efflux activity.
Collapse
Affiliation(s)
- Linliang Yu
- Department of Chemistry, University of Kentucky, Lexington, Kentucky, United States of America
| | - Wei Lu
- Department of Chemistry, University of Kentucky, Lexington, Kentucky, United States of America
| | - Yinan Wei
- Department of Chemistry, University of Kentucky, Lexington, Kentucky, United States of America
- * E-mail:
| |
Collapse
|
18
|
Bosse M, Thomas L, Hassert R, Beck-Sickinger AG, Huster D, Schmidt P. Assessment of a fully active class A G protein-coupled receptor isolated from in vitro folding. Biochemistry 2011; 50:9817-25. [PMID: 21999704 DOI: 10.1021/bi201320e] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We provide a protocol for the preparation of fully active Y2 G protein-coupled receptors (GPCRs). Although a valuable target for pharmaceutical research, information about the structure and dynamics of these molecules remains limited due to the difficulty in obtaining sufficient amounts of homogeneous and fully active receptors for in vitro studies. Recombinant expression of GPCRs as inclusion bodies provides the highest protein yields at lowest costs. But this strategy can only successfully be applied if the subsequent in vitro folding results in a high yield of active receptors and if this fraction can be isolated from the nonactive receptors in a homogeneous form. Here, we followed that strategy to provide large quantities of the human neuropeptide Y receptor type 2 and determined the folding yield before and after ligand affinity chromatography using a radioligand binding assay. Directly after folding, we achieved a proportion of ~25% active receptor. This value could be increased to ~96% using ligand affinity chromatography. Thus, a very homogeneous sample of the Y2 receptor could be prepared that exhibited a K(D) value of 0.1 ± 0.05 nM for the binding of polypeptide Y, which represents one of the natural ligands of the Y2 receptor.
Collapse
Affiliation(s)
- Mathias Bosse
- Institute of Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16-18, D-04107 Leipzig, Germany
| | | | | | | | | | | |
Collapse
|