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使用单分子FRET可视化膜受体的构象动力学

Published: August 17, 2022
doi:

Özet

本研究提出了一种详细的程序,通过非天然氨基酸(UAA)掺入 使用 位点特异性标记对G蛋白偶联受体(GPCR)进行单分子荧光共振能量转移(smFRET)实验。该协议为 smFRET 样品制备、实验和数据分析提供了分步指南。

Abstract

细胞对外部信号做出反应的能力对于细胞发育、生长和存活至关重要。为了响应来自环境的信号,细胞必须能够识别和处理它。这项任务主要依靠膜受体的功能,膜受体的作用是将信号转化为细胞的生化语言。G蛋白偶联受体(GPCR)是人类最大的膜受体蛋白家族。在GPCR中,代谢性谷氨酸受体(mGluR)是一个独特的亚类,其功能是专性二聚体,并具有包含配体结合位点的大细胞外结构域。mGluR结构研究的最新进展提高了对其活化过程的理解。然而,在激活和调制过程中通过mGluR传播大规模构象变化知之甚少。单分子荧光共振能量转移(smFRET)是一种在单蛋白水平上可视化和量化生物分子结构动力学的强大技术。为了可视化mGluR2活化的动态过程,开发了基于非天然氨基酸(UAA)掺入的荧光构象传感器,该传感器允许位点特异性蛋白质标记而不会干扰受体的天然结构。此处描述的协议解释了如何执行这些实验,包括新型UAA标记方法,样品制备以及smFRET数据采集和分析。这些策略是可推广的,可以扩展到研究各种膜蛋白的构象动力学。

Introduction

跨质膜的信息传递在很大程度上取决于膜受体的功能1。配体与受体结合导致构象变化和受体活化。这个过程在本质上通常是变构的2.G蛋白偶联受体(GPCR)拥有800多个成员,是人类最大的膜受体家族3。由于其在几乎所有细胞过程中的作用,GPCR已成为治疗开发的重要靶标。在GPCR信号传导的典型模型中,激动剂激活导致受体的构象变化,随后通过在Gα的核苷酸结合口袋中将GDP交换为GTP激活异源三聚体G蛋白复合物。活化的Gα-GTP和Gβγ亚基然后控制下游效应蛋白的活性并传播信号级联45。这种信号传导过程基本上取决于配体改变受体三维形状的能力。对配体如何实现这一目标的机制理解对于开发新疗法和设计合成受体和传感器至关重要。

代谢性谷氨酸受体(mGluRs)是C类GPCR家族的成员,对于谷氨酸的缓慢神经调节作用和调节神经元兴奋性很重要67。在所有GPCR中,C类GPCR在结构上是独一无二的,因为它们作为专性二聚体起作用。mGluR包含三个结构域:金星捕蝇器(VFT)结构域,富含半胱氨酸的结构域(CRD)和跨膜结构域(TMD)8。活化过程中的构象变化是复杂的,涉及在12 nm距离上传播的局部和全局构象耦合,以及二聚体的协同性。中间构象、状态的时间顺序和状态之间的转换速率是未知的。通过实时跟踪单个受体的构象,可以识别瞬时中间状态和激活过程中构象变化的序列。这可以通过应用单分子荧光共振能量转移910(smFRET)来实现就像最近应用于可视化mGluR211活化过程中构象变化的传播一样。FRET实验的一个关键步骤是通过将供体和受体荧光团插入目标蛋白质的位点特异性插入来生成FRET传感器。采用非天然氨基酸(UAA)掺入策略12,131415克服典型的位点特异性荧光标记技术的局限性该技术需要创建无半胱氨酸突变体或插入大型基因编码标签。这允许观察到基本的致密变构接头的构象重排,该接头连接了mGluR2的配体结合和信号结构域。在该协议中,提供了在mGluR2上进行smFRET实验的分步指南,包括使用UAA对mGluR2进行位点特异性标记以使用铜催化叠氮化物环化反应附着荧光团的方法。此外,该协议描述了直接捕获膜蛋白和数据分析的方法。此处概述的方案也适用于研究其他膜蛋白的构象动力学。

Protocol

该协议的整体工作流程如图 1 所示。 1. 样品室的准备 玻片和盖玻片清洁注意:这些步骤旨在清洁载玻片的表面以及盖玻片,并为氨基硅烷化做好准备。对表面束缚分子进行单分子荧光实验的一个关键要求是钝化表面。最可靠和可重复的钝化技术涉及将惰性聚合物链作为致密层共价附着到玻璃表面。聚乙二醇(PEG)是用于表面钝化的最有效?…

Representative Results

基于UAA的FRET传感器的表达和荧光标记本文讨论了在mGluR2(548UAA)的CRD内插入和荧光标记UAA(AZP)的示例性结果11。如前所述,要将AZP插入mGluR2中,工程翻译机制的共表达是必要的,其中包括修饰的tRNA合成酶和互补tRNA(pIRE4-Azi),以及使用诱变创建的在位置548处含有琥珀色密码子的mGluR2(图2A,B)。通过铜催化的环加成反应(<st…

Discussion

GPCR是在细胞膜上起作用以启动信号转导的蛋白质。许多GPCR由多个域组成,信令依赖于域之间的合作相互作用。为了调节这些膜受体的性质,必须了解多个结构域的动态行为。单分子荧光共振能量转移(smFRET)是一种荧光技术,能够实时测量蛋白质构象和动力学1132。这里描述了一种结合smFRET,单分子下拉(SiMPull)和全内反射荧光(T…

Açıklamalar

The authors have nothing to disclose.

Acknowledgements

我们感谢Reza Vafabakhsh实验室成员的讨论。这项工作得到了美国国立卫生研究院拨款R01GM140272(R.V.),西北大学Searle生命科学领导基金和芝加哥生物医学联盟的支持,并得到了芝加哥社区信托基金的Searle基金(对R.V.)的支持。B.W.L.得到了美国国家普通医学科学研究所(NIGMS)培训补助金T32GM-008061的支持。

Materials

(+)-Sodium L-Ascorbate Sigma Aldrich Cat # 11140-250G
4-azido-L-phenylalanine Chem-Impex International Cat # 06162
548UAA Liauw et al. 2021 Transfected construct
Acetic Acid Fisher Chemical 64-19-7
Acetone Fisher Chemical 67-64-1
Adobe Illustrator (2022) https://www.adobe.com/ RRID:SCR_010279 Software, algorithm
Aminoguanidine (hydrochloride) Cayman Chemical 81530
Aminosilane Aldrich 919-30-2
Bath Sonicator 2.8 L Fisher Scientific Ultrasonic Bath 2.8 L
Biotin-PEG Laysan Bio Inc Item# Biotin-PEG-SVA-5000-100mg
BTTES Click Chemistry Tools 1237-500
Copper (II) sulfate Sigma Aldrich Cat # 451657-10G
Cover slip VWR 16004-306 Sample chamber
Cy3 Alkyne Click Chemistry Tools TA117-5
Cy5 Alkyne Click Chemistry Tools TA116-5
DDM Anatrace Part# D310 1 GM Detergent
DDM-CHS (10:1) Anatrace Part# D310-CH210 1 ML Detergent with cholecterol
Defined Fetal Bovine Serum Thermo Fisher Scientific SH30070.03
Di01-R405/488/561/635 Semrock Notch filter
DMEM Corning 10-013-CV
EMCCD Andor DU-897U Camera
ET542lp Chroma Long pass emission filter
FF640-FDi01 Semrock Emission dichroic filter
FLAG-tag antibody Genscript A01429
Fluorescent bead Invitrogen T7279 TetraSpeck microspheres Spherical bead
Glass slides Fisherfinest 12-544-4 sample chamber
Glutamate Sigma Aldrich Cat # 6106-04-3
HEK 293T Sigma Aldrich Cat # 12022001 Cell line
HEPES FisherBioReagents 7365-45-9
Image splitter OptoSplit II
KOH Fluka 1310-58-3
Laser Oxxius 4-line laser combiner
Lipofectamine 3000 Transfection Reagent Thermo Fisher Scientific L3000015 Transfection Reagent
Methanol Fisher Chemical 67-56-1
Microscope Olympus Olympus IX83
Milli-Q water Barnstead Water Deionizer
m-PEG Laysan Bio Inc Item# MPEG-SIL-5000-1g
NF03-405/488/532/635 Semrock Dichroic mirror
OptiMEM Thermo Fisher Scientific 51985091 Reduced Serum Medium
OptiMEM/Reduced serum medium Thermo Fisher Scientific
OriginPro (2020b) https://www.originlab.com/ RRID:SCR_014212 Data analysis and graphing software
Penicillin-Streptomycin Gibco 15140-122
pIRE4-Azi Addgene Plasmid # 105829 Transfected construct
Poly-L-lysine hydrobromide Sigma Aldrich Cat # P2636
Protocatechuic acid (PCA) HWI group 99-50-3
smCamera (Version 1.0) http://ha.med.jhmi.edu/resources/ Camera software
Sodium bicarbonate FisherBioReagents 144-55-8
Sodium hydroxide (NaOH) Sigma 1310-73-2
Syringe filter Whatman UNIFLO Cat#9914-2502 Liquid filtration
Trolox Sigma 53188-07

Referanslar

  1. Smock, R. G., Gierasch, L. M. Sending signals dynamically. Science. 324 (5924), 198-203 (2009).
  2. Changeux, J. P., Christopoulos, A. Allosteric modulation as a unifying mechanism for receptor function and regulation. Cell. 166 (5), 1084-1102 (2016).
  3. Tang, X. -. l., Wang, Y., Li, D. -. l., Luo, J., Liu, M. -. Y. Orphan G protein-coupled receptors (GPCRs): biological functions and potential drug targets. Acta Pharmacologica Sinica. 33 (3), 363-371 (2012).
  4. Chung, K. Y., et al. Conformational changes in the G protein Gs induced by the β2 adrenergic receptor. Nature. 477 (7366), 611-615 (2011).
  5. Vafabakhsh, R., Levitz, J., Isacoff, E. Y. Conformational dynamics of a class C G-protein-coupled receptor. Nature. 524 (7566), 497-501 (2015).
  6. Niswender, C. M., Conn, P. J. Metabotropic glutamate receptors: Physiology, pharmacology, and disease. Annual Review of Pharmacology and Toxicology. 50, 295-322 (2010).
  7. Pin, J. P., Bettler, B. Organization and functions of mGlu and GABA(B) receptor complexes. Nature. 540 (7631), 60-68 (2016).
  8. Kniazeff, J., et al. Closed state of both binding domains of homodimeric mGlu receptors is required for full activity. Nature Structural & Molecular Biology. 11 (8), 706-713 (2004).
  9. Ha, T. Single-molecule fluorescence resonance energy transfer. Methods. 25 (1), 78-86 (2001).
  10. Schuler, B., Eaton, W. A. Protein folding studied by single-molecule FRET. Current Opinion in Structural Biology. 18 (1), 16-26 (2008).
  11. Liauw, B. W. -. H., Afsari, H. S., Vafabakhsh, R. Conformational rearrangement during activation of a metabotropic glutamate receptor. Nature Chemical Biology. 17 (3), 291-297 (2021).
  12. Noren, C. J., Anthonycahill, S. J., Griffith, M. C., Schultz, P. G. A general method for site-specific incorporation of unnatural amino acids into proteins. Science. 244 (4901), 182-188 (1989).
  13. Presolski, S. I., Hong, V. P., Finn, M. Copper-catalyzed azide-alkyne click chemistry for bioconjugation. Current Protocols in Chemical Biology. 3 (4), 153-162 (2011).
  14. Huber, T., Naganathan, S., Tian, H., Ye, S. X., Sakmar, T. P. Unnatural amino acid mutagenesis of GPCRs using amber codon suppression and bioorthogonal labeling. G Protein Coupled Receptors: Structure. 520, 281-305 (2013).
  15. Serfling, R., Coin, I., Pecoraro, V. Chapter Four – Incorporation of Unnatural Amino Acids into Proteins Expressed in Mammalian Cells. Methods in Enzymology. 580, 89-107 (2016).
  16. Chandradoss, S. D., et al. Surface passivation for single-molecule protein studies. Journal of Visualized Experiments. (86), e50549 (2014).
  17. Rasnik, I., McKinney, S. A., Ha, T. Nonblinking and long-lasting single-molecule fluorescence imaging. Nature Methods. 3 (11), 891-893 (2006).
  18. Cordes, T., Vogelsang, J., Tinnefeld, P. On the mechanism of Trolox as antiblinking and antibleaching reagent. Journal of the American Chemical Society. 131 (14), 5018-5019 (2009).
  19. Aitken, C. E., Marshall, R. A., Puglisi, J. D. An oxygen scavenging system for improvement of dye stability in single-molecule fluorescence experiments. Biophysical Journal. 94 (5), 1826-1835 (2008).
  20. Lee, S., et al. How do short chain nonionic detergents destabilize G-protein-coupled receptors. Journal of the American Chemical Society. 138 (47), 15425-15433 (2016).
  21. Cao, A. -. M., et al. Allosteric modulators enhance agonist efficacy by increasing the residence time of a GPCR in the active state. Nature Communications. 12 (1), 1-13 (2021).
  22. Mancebo, A., Mehra, D., Banerjee, C., Kim, D. -. H., Puchner, E. M. Efficient cross-correlation filtering of one-and two-color single molecule localization microscopy data. Frontiers in Bioinformatics. 1, 739769 (2021).
  23. Mehra, D., Adhikari, S., Banerjee, C., Puchner, E. M. Characterizing locus specific chromatin structure and dynamics with correlative conventional and super-resolution imaging in living cells. Nucleic Acids Research. , (2022).
  24. Chen, H., Puhl, H. L., Koushik, S. V., Vogel, S. S., Ikeda, S. R. Measurement of FRET efficiency and ratio of donor to acceptor concentration in living cells. Biophysical Journal. 91 (5), 39-41 (2006).
  25. Gopich, I. V., Szabo, A. FRET efficiency distributions of multistate single molecules. The Journal of Physical Chemistry B. 114 (46), 15221-15226 (2010).
  26. Roy, R., Hohng, S., Ha, T. A practical guide to single-molecule FRET. Nature Methods. 5 (6), 507-516 (2008).
  27. Hellenkamp, B., et al. Precision and accuracy of single-molecule FRET measurements-A multi-laboratory benchmark study. Nature Methods. 15 (9), 669-676 (2018).
  28. Bronson, J. E., Fei, J., Hofman, J. M., Gonzalez, R. L., Wiggins, C. H. Learning rates and states from biophysical time series: A Bayesian approach to model selection and single-molecule FRET data. Biophysical Journal. 97 (12), 3196-3205 (2009).
  29. Zhang, J., et al. Specific structural elements of the T-box riboswitch drive the two-step binding of the tRNA ligand. Elife. 7, 39518 (2018).
  30. Goodman, N. R. Statistical analysis based on a certain multivariate complex Gaussian distribution (an introduction). The Annals of Mathematical Statistics. 34 (1), 152-177 (1963).
  31. Brown, R. B., Audet, J. Current techniques for single-cell lysis. Journal of the Royal Society Interface. 5, 131-138 (2008).
  32. Schamber, M. R., Vafabakhsh, R. Mechanism of sensitivity modulation in the calcium-sensing receptor via electrostatic tuning. Nature Communications. 13 (1), 2194 (2022).
  33. Jain, A., Liu, R., Xiang, Y. K., Ha, T. Single-molecule pull-down for studying protein interactions. Nature Protocols. 7 (3), 445-452 (2012).
  34. Huang, S. K., et al. Delineating the conformational landscape of the adenosine A(2A) receptor during G protein coupling. Cell. 184 (7), 1884-1894 (2021).
  35. Wingler, L. M., et al. Angiotensin analogs with divergent bias stabilize distinct receptor conformations. Cell. 176 (3), 468-478 (2019).
  36. Gordon, C. G., et al. Reactivity of biarylazacyclooctynones in copper-free click chemistry. Journal of the American Chemical Society. 134 (22), 9199-9208 (2012).
  37. Kim, E., Koo, H. Biomedical applications of copper-free click chemistry: In vitro, in vivo, and ex vivo. Chemical Science. 10 (34), 7835-7851 (2019).
  38. Pickens, C. J., Johnson, S. N., Pressnall, M. M., Leon, M. A., Berkland, C. J. Practical considerations, challenges, and limitations of bioconjugation via azide-alkyne cycloaddition. Bioconjugate Chemistry. 29 (3), 686-701 (2018).
  39. Geng, Y., et al. Structural mechanism of ligand activation in human calcium-sensing receptor. Elife. 5, 13662 (2016).

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Bu Makaleden Alıntı Yapın
Banerjee, C., Liauw, B. W., Vafabakhsh, R. Visualizing the Conformational Dynamics of Membrane Receptors Using Single-Molecule FRET. J. Vis. Exp. (186), e64254, doi:10.3791/64254 (2022).

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