Name: visualizing the conformational dynamics of membrane receptors using single-molecule fret
Uploaded: 2022-08-17T14:15:00.000+00:00
Duration: 10 min 59 s
Description: Watch this Scientific Journal Video about Visualizing the Conformational Dynamics of Membrane Receptors Using Single-Molecule FRET at JoVE.com

We thank members of the Reza Vafabakhsh lab for discussions. This work was supported by the National Institutes of Health grant R01GM140272 (to R.V.), by The Searle Leadership Fund for the Life Sciences at Northwestern University, and by the Chicago Biomedical Consortium with support from the Searle Funds at The Chicago Community Trust (to R.V.). B.W.L. was supported by the National Institute of General Medical Sciences (NIGMS) Training Grant T32GM-008061.

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The authors declare no competing interests.

GPCRs are proteins that operate on the cell membrane to initiate signal transduction. Many GPCRs consist of multiple domains, with signaling being dependent on the cooperative interaction between the domains. To modulate the properties of these membrane receptors, it is essential to understand the dynamic behavior of the multiple domains. Single-molecule fluorescence resonance energy transfer (smFRET) is a fluorescence technique that enables the measurement of protein conformation and dynamics in real time<sup class="xre...

The transfer of information across the plasma membrane is heavily dependent on the function of membrane receptors1. Ligand binding to a receptor leads to a conformational change and receptor activation. This process is often allosteric in nature2. With over 800 members, G protein-coupled receptors (GPCRs) are the largest family of membrane receptors in humans3. Due to their role in nearly all cellular processes, GPCRs have become important targets for therapeutic development. In the canonical model of GPCR signaling, agonist activation results in conformational changes of the receptor that subsequently activate the heterotrimeric G protein complex via exchange of GDP for GTP at the nucleotide binding pocket of G&#945;. The activated G&#945;-GTP and G&#946;&#947; subunits then control the activity of downstream effector proteins and propagate the signaling cascade4,5. This signaling process essentially depends on the ability of ligands to change the three-dimensional shape of the receptor. A mechanistic understanding of how ligands achieve this is critical for developing new therapeutics and designing synthetic receptors and sensors.
Metabotropic glutamate receptors (mGluRs) are members of the class C GPCR family and are important for the slow neuromodulatory effects of glutamate and tuning neuronal excitability6,7. Among all GPCRs, class C GPCRs are structurally unique in that they function as obligate dimers. mGluRs contain three structural domains: the Venus flytrap (VFT) domain, cysteine-rich domain (CRD), and transmembrane domain (TMD)8. The conformational changes during the activation process are complex and involve local and global conformational coupling that propagate over a 12 nm distance, as well as dimer cooperativity. The intermediate conformations, temporal ordering of states, and rate of transition between states are unknown. By following the conformation of individual receptors in real time, it is possible to identify the transient intermediate states and the sequence of conformational changes during activation. This can be achieved by applying single-molecule fluorescence resonance energy transfer9,10 (smFRET), as was recently applied to visualize the propagation of conformational changes during the activation of mGluR211. A key step in FRET experiments is the generation of FRET sensors by site-specific insertion of the donor and acceptor fluorophores into the protein of interest. An unnatural amino acid (UAA) incorporation strategy was adopted12,13,14,15 to overcome the limitations of typical site-specific fluorescent labeling technologies that require the creation of cysteine-less mutants or the insertion of a large genetically encoded tag. This allowed the conformational rearrangement of the essential compact allosteric linker, which joined the ligand-binding and signaling domains of mGluR2, to be observed. In this protocol, a step-by-step guide to performing smFRET experiments on mGluR2 is presented, including the approach for site-specific labeling of mGluR2 with UAA to attach fluorophores using the copper-catalyzed azide cyclization reaction. Moreover, this protocol describes the methodology for the direct capture of membrane proteins and data analysis. The protocol outlined here is also applicable to studying the conformational dynamics of other membrane proteins.

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

visualizing the conformational dynamics of membrane receptors using single-molecule fret

The ability of cells to respond to external signals is essential for cellular development, growth, and survival. To respond to a signal from the environment, a cell must be able to recognize and process it. This task mainly relies on the function of membrane receptors, whose role is to convert signals into the biochemical language of the cell. G protein-coupled receptors (GPCRs) constitute the largest family of membrane receptor proteins in humans. Among GPCRs, metabotropic glutamate receptors (mGluRs) are a unique subclass that function as obligate dimers and possess a large extracellular domain that contains the ligand-binding site. Recent advances in structural studies of mGluRs have improved the understanding of their activation process. However, the propagation of large-scale conformational changes through mGluRs during activation and modulation is poorly understood. Single-molecule fluorescence resonance energy transfer (smFRET) is a powerful technique to visualize and quantify the structural dynamics of biomolecules at the single-protein level. To visualize the dynamic process of mGluR2 activation, fluorescent conformational sensors based on unnatural amino acid (UAA) incorporation were developed that allowed site-specific protein labeling without perturbation of the native structure of receptors. The protocol described here explains how to perform these experiments, including the novel UAA labeling approach, sample preparation, and smFRET data acquisition and analysis. These strategies are generalizable and can be extended to investigate the conformational dynamics of a variety of membrane proteins.

Expression and fluorescent labeling of UAA-based FRET sensor 
Herein, exemplary results of the insertion and fluorescent labeling of a UAA (AZP) within the CRD of mGluR2 (548UAA) are discussed11. As mentioned previously, to insert AZP into mGluR2, co-expression of the engineered translational machinery, which includes a modified tRNA synthetase and complementary tRNA (pIRE4-Azi), and mGluR2 containing an amber codon at position 548, created using mutagenesis, is necessary (<s...

Watch this Scientific Journal Video about Visualizing the Conformational Dynamics of Membrane Receptors Using Single-Molecule FRET at JoVE.com

Visualizing the Conformational Dynamics of Membrane Receptors Using Single-Molecule FRET

This study presents a detailed procedure to perform single-molecule fluorescence resonance energy transfer (smFRET) experiments on G protein-coupled receptors (GPCRs) using site-specific labeling via unnatural amino acid (UAA) incorporation. The protocol provides a step-by-step guide for smFRET sample preparation, experiments, and data analysis.

The ability of cells to respond to external signals is essential for cellular development, growth, and survival. To respond to a signal from the ...

visualizing-conformational-dynamics-membrane-receptors-using-single

Research

JoVE Journal

Biochemistry

3.1K Views.  Northwestern University. This study presents a detailed procedure to perform single-molecule fluorescence resonance energy transfer (smFRET) experiments on G protein-coupled receptors (GPCRs) using site-specific labeling via unnatural amino acid (UAA) incorporation. The protocol provides a step-by-step guide for smFRET sample preparation, experiments, and data analysis.

Video: Visualizing the Conformational Dynamics of Membrane Receptors Using Single-Molecule FRET

High Precision FRET at Single-molecule Level for Biomolecule Structure Determination

A protocol on how to perform high-precision interdye distance measurements using F&#246;rster resonance energy transfer (FRET) at the single-molecule level in multiparameter fluorescence detection (MFD) mode is presented here. MFD maximizes the usage of all &#34;dimensions&#34; of fluorescence to reduce photophysical and experimental artifacts and allows for the measurement of interdye distance with an accuracy up to ~1 &#197; in rigid biomolecules. This method was used to identify three conformational states of the ligand-binding domain of the N-methyl-D-aspartate (NMDA) receptor to explain the activation of the receptor upon ligand binding. When comparing the known crystallographic structures with experimental measurements, they agreed within less than 3 &#197; for more dynamic biomolecules. Gathering a set of distance restraints that covers the entire dimensionality of the biomolecules would make it possible to provide a structural model of dynamic biomolecules.

A protocol for high-precision FRET experiments at the single molecule level is presented here. Additionally, this methodology can be used to identify three conformational states in the ligand-binding domain of the N-methyl-D-aspartate (NMDA) receptor. Determining precise distances is the first step towards building structural models based on FRET experiments.

A protocol on how to perform high-precision interdye distance measurements using F&#246;rster resonance energy transfer (FRET) at the single-molecule ...

Using Three-color Single-molecule FRET to Study the Correlation of Protein Interactions

Single-molecule F&#246;rster resonance energy transfer (smFRET) has become a widely used biophysical technique to study the dynamics of biomolecules. For many molecular machines in a cell proteins have to act together&#160;with interaction partners in a functional cycle to fulfill their task. The extension of two-color to multi-color smFRET makes it possible to simultaneously probe more than one interaction or conformational change. This not only adds a new dimension to smFRET experiments but it also offers the unique possibility to directly study the sequence of events and to detect correlated interactions when using an immobilized sample and a total internal reflection fluorescence microscope (TIRFM). Therefore, multi-color smFRET is a versatile tool for studying biomolecular complexes in a quantitative manner and in a previously unachievable detail.
Here, we demonstrate how to overcome the special challenges of multi-color smFRET experiments on proteins. We present detailed protocols for obtaining the data and for extracting kinetic information. This includes trace selection criteria, state separation, and the recovery of state trajectories from the noisy data using a 3D ensemble Hidden Markov Model (HMM). Compared to other methods, the kinetic information is not recovered from dwell time histograms but directly from the HMM. The maximum likelihood framework allows us to critically evaluate the kinetic model and to provide meaningful uncertainties for the rates.
By applying our method to the heat shock protein 90 (Hsp90), we are able to disentangle the nucleotide binding and the global conformational changes of the protein. This allows us to directly observe the cooperativity between the two nucleotide binding pockets of the Hsp90 dimer.

Here, we present a protocol to obtain three-color smFRET data and its analysis with a 3D ensemble Hidden Markov Model. With this approach, scientists can extract kinetic information from complex protein systems, including cooperativity or correlated interactions.

Single-molecule F&#246;rster resonance energy transfer (smFRET) has become a widely used biophysical technique to study the dynamics of biomolecules. For ...

High-resolution Spatiotemporal Analysis of Receptor Dynamics by Single-molecule Fluorescence Microscopy

Single-molecule microscopy is emerging as a powerful approach to analyze the behavior of signaling molecules, in particular concerning those aspect (e.g., kinetics, coexistence of different states and populations, transient interactions), which are typically hidden in ensemble measurements, such as those obtained with standard biochemical or microscopy methods. Thus, dynamic events, such as receptor-receptor interactions, can be followed in real time in a living cell with high spatiotemporal resolution. This protocol describes a method based on labeling with small and bright organic fluorophores and total internal reflection fluorescence (TIRF) microscopy to directly visualize single receptors on the surface of living cells. This approach allows one to precisely localize receptors, measure the size of receptor complexes, and capture dynamic events such as transient receptor-receptor interactions. The protocol provides a detailed description of how to perform a single-molecule experiment, including sample preparation, image acquisition and image analysis. As an example, the application of this method to analyze two G-protein-coupled receptors, i.e., &#946;2-adrenergic and &#947;-aminobutyric acid type B (GABAB) receptor, is reported. The protocol can be adapted to other membrane proteins and different cell models, transfection methods and labeling strategies.

This protocol describes how to use total internal reflection fluorescence microscopy to visualize and track single receptors on the surface of living cells and thereby analyze receptor lateral mobility, size of receptor complexes as well as to visualize transient receptor-receptor interactions. This protocol can be extended to other membrane proteins.

Single-molecule microscopy is emerging as a powerful approach to analyze the behavior of signaling molecules, in particular concerning those aspect (e.g., ...

Bioengineering

Measuring TCR-pMHC Binding In Situ using a FRET-based Microscopy Assay

T-cells are remarkably specific and effective when recognizing antigens in the form of peptides embedded in MHC molecules (pMHC) on the surface of Antigen Presenting Cells (APCs). This is despite T-cell antigen receptors (TCRs) exerting usually a moderate affinity (&#181;M range) to antigen when binding is measured in vitro1. In view of the molecular and cellular parameters contributing to T-cell antigen sensitivity, a microscopy-based methodology has been developed as a means to monitor TCR-pMHC binding in situ, as it occurs within the synapse of a live T-cell and an artificial and functionalized glass-supported planar lipid bilayer (SLB), which mimics the cell membrane of an Antigen presenting Cell (APC) 2. Measurements are based on F&#246;rster Resonance Energy Transfer (FRET) between a blue- and red-shifted fluorescent dye attached to the TCR and the pMHC. Because the efficiency of FRET is inversely proportional to the sixth power of the inter-dye distance, one can employ FRET signals to visualize synaptic TCR-pMHC binding. The sensitive of the microscopy approach supports detection of single molecule FRET events. This allows to determine the affinity and off-rate of synaptic TCR-pMHC interactions and in turn to interpolate the on-rate of binding. Analogous assays could be applied to measure other receptor-ligand interactions in their native environment.

Measuring TCR-pMHC Binding In Situ using a FRET-based Microscopy Assay

This manuscript describes how to conduct (single molecule) F&#246;rster Resonance Energy Transfer (FRET)- based assays to measure the binding dynamics between T-cell antigen receptor (TCR) and antigenic peptide-loaded MHC molecules as they occur within the immunological synapse of a T-cell in contact with a functionalized planar supported lipid bilayer.

T-cells are remarkably specific and effective when recognizing antigens in the form of peptides embedded in MHC molecules (pMHC) on the surface of Antigen ...

Examining the Conformational Dynamics of Membrane Proteins in situ with Site-directed Fluorescence Labeling

Two electrode voltage clamp electrophysiology (TEVC) is a powerful tool to investigate the mechanism of ion transport1 for a wide variety of membrane proteins including ion channels2, ion pumps3, and transporters4. Recent developments have combined site-specific fluorophore labeling alongside TEVC to 
concurrently examine the conformational dynamics at specific residues and function of these proteins on the surface of single cells.
We will describe a method to study the conformational dynamics of membrane proteins by simultaneously monitoring fluorescence and current changes using voltage-clamp fluorometry. This approach can be used to examine the molecular motion of membrane proteins site-specifically following cysteine replacement and site-directed fluorophore labeling5,6. Furthermore, this method provides an approach to determine distance constraints between specific residues7,8. 
This is achieved by selectively attaching donor and acceptor fluorophores to two mutated cysteine residues of interest.
In brief, these experiments are performed following functional expression of the desired protein on the surface of Xenopus leavis oocytes. The large surface area of these oocytes enables facile functional measurements and a robust fluorescence signal5. It is also possible to readily change the extracellular conditions such as pH, ligand or cations/anions, which can provide further information on the mechanism of membrane proteins4. Finally, recent developments 
have also enabled the manipulation of select internal ions following co-expression with a second protein9.
Our protocol is described in multiple parts. First, cysteine scanning mutagenesis proceeded by fluorophore labeling is completed at residues located at the interface of the transmembrane and extracellular domains. Subsequent experiments are designed to identify residues which demonstrate large changes in fluorescence intensity (&lt;5%)3 upon a conformational change of the protein. Second, these changes in fluorescence intensity are compared to the kinetic parameters of 
the membrane protein in order to correlate the conformational dynamics to the function of the protein10. This enables a rigorous biophysical analysis of the molecular motion of the target protein. Lastly, two residues of the holoenzyme can be labeled with a donor and acceptor fluorophore in order to determine distance constraints using donor photodestruction methods. It is also possible to monitor the relative movement of protein subunits following labeling with a donor and acceptor fluorophore.

Examining the Conformational Dynamics of Membrane Proteins in situ with Site-directed Fluorescence Labeling

We will describe a method which measures the kinetics of ion transport of membrane proteins alongside site-specific analysis of conformational changes using fluorescence on single cells. This technique is adaptable to ion channels, transporters and ion pumps and can be utilized to determine distance constraints between protein subunits.

Two electrode voltage clamp electrophysiology (TEVC) is a powerful tool to investigate the mechanism of ion transport1 for a wide variety of membrane ...

Biology

Visualizing Intracellular SNARE Trafficking by Fluorescence Lifetime Imaging Microscopy

Soluble N-ethylmaleimide sensitive fusion protein (NSF) attachment protein receptor (SNARE) proteins are key for membrane trafficking, as they catalyze membrane fusion within eukaryotic cells. The SNARE protein family consists of about 36 different members. Specific intracellular transport routes are catalyzed by specific sets of 3 or 4 SNARE proteins that thereby contribute to the specificity and fidelity of membrane trafficking. However, studying the precise function of SNARE proteins is technically challenging, because SNAREs are highly abundant and functionally redundant, with most SNAREs having multiple and overlapping functions. In this protocol, a new method for the visualization of SNARE complex formation in live cells is described. This method is based on expressing SNARE proteins C-terminally fused to fluorescent proteins and measuring their interaction by F&#246;rster resonance energy transfer (FRET) employing fluorescence lifetime imaging microscopy (FLIM). By fitting the fluorescence lifetime histograms with a multicomponent decay model, FRET-FLIM allows (semi-)quantitative estimation of the fraction of the SNARE complex formation at different vesicles. This protocol has been successfully applied to visualize SNARE complex formation at the plasma membrane and at endosomal compartments in mammalian cell lines and primary immune cells, and can be readily extended to study SNARE functions at other organelles in animal, plant, and fungal cells.

This protocol describes a new method allowing for the quantitative visualization of complex formation of SNARE proteins, based on F&#246;rster resonance energy transfer, and fluorescence lifetime imaging microscopy.

Soluble N-ethylmaleimide sensitive fusion protein (NSF) attachment protein receptor (SNARE) proteins are key for membrane trafficking, as they catalyze ...

Immunology and Infection

Monitoring GTPase Atlastin in Different Nucleotide Loading States

Single-Molecule FRET Imaging for Observing the Conformational Dynamics of Dynamin-Like GTPase Atlastin

The rigid-body rotation of the three-helical middle domain (3HB) relative to the GTPase domain of dynamin-like protein atlastin (ATL) is a crucial driver of homotypic membrane fusion within the endoplasmic reticulum (ER). Disruptions in this process have been associated with hereditary spastic paraplegia (HSP), a neurodegenerative disorder. Structural and biochemical studies suggest that the conformational changes in ATL are linked to GTP hydrolysis, but real-time visualization of these conformational dynamics during the GTP hydrolysis cycle remains challenging. To better understand the mechanical mechanisms behind ATL function, single-molecule F&#246;rster resonance energy transfer (smFRET) was utilized. Three specific strategies were employed to immobilize the N-terminal cytosolic region of human ATL1 (ATL1cyto) in a streptavidin-coated microfluidic chamber, facilitating the application of intramolecular and intermolecular smFRET imaging. This allowed precise monitoring of protein conformations in various nucleotide-loading states, providing direct insights into individual molecular behaviors. This method can be applied to study other mechanochemical proteins as well.

The functions of dynamin superfamily proteins depend on conformational changes coupled with GTP hydrolysis. A system is described using the single-molecule FRET (smFRET) technique to monitor the conformational dynamics of dynamin-like GTPase atlastin in different nucleotide-loading states.

The rigid-body rotation of the three-helical middle domain (3HB) relative to the GTPase domain of dynamin-like protein atlastin (ATL) is a crucial driver ...

FRET Microscopy for Real-time Monitoring of Signaling Events in Live Cells Using Unimolecular Biosensors

F&ouml;rster resonance energy transfer (FRET) microscopy continues to gain increasing interest as a technique for real-time monitoring of biochemical and signaling events in live cells and tissues. Compared to classical biochemical methods, this novel technology is characterized by high temporal and spatial resolution. FRET experiments use various genetically-encoded biosensors which can be expressed and imaged over time in situ or in vivo1-2. Typical biosensors can either report protein-protein interactions by measuring FRET between a fluorophore-tagged pair of proteins or conformational changes in a single protein which harbors donor and acceptor fluorophores interconnected with a binding moiety for a molecule of interest3-4. Bimolecular biosensors for protein-protein interactions include, for example, constructs designed to monitor G-protein activation in cells5, while the unimolecular sensors measuring conformational changes are widely used to image second messengers such as calcium6, cAMP7-8, inositol phosphates9 and cGMP10-11. Here we describe how to build a customized epifluorescence FRET imaging system from single commercially available components and how to control the whole setup using the Micro-Manager freeware. This simple but powerful instrument is designed for routine or more sophisticated FRET measurements in live cells. Acquired images are processed using self-written plug-ins to visualize changes in FRET ratio in real-time during any experiments before being stored in a graphics format compatible with the build-in ImageJ freeware used for subsequent data analysis. This low-cost system is characterized by high flexibility and can be successfully used to monitor various biochemical events and signaling molecules by a plethora of available FRET biosensors in live cells and tissues. As an example, we demonstrate how to use this imaging system to perform real-time monitoring of cAMP in live 293A cells upon stimulation with a &beta;-adrenergic receptor agonist and blocker.

F&#246;rster resonance energy transfer (FRET) microscopy is a powerful technique for real-time monitoring of signaling events in live cells using various biosensors as reporters. Here we describe how to build a customized epifluorescence FRET imaging system from commercially available components and how to use it for FRET experiments.

F&ouml;rster resonance energy transfer (FRET) microscopy  continues to gain increasing interest as a technique for real-time monitoring  of biochemical ...

Automated Two-dimensional Spatiotemporal Analysis of Mobile Single-molecule FRET Probes

Single-molecule F&#246;rster resonance energy transfer (smFRET) is a versatile technique reporting on distances in the sub-nanometer to nanometer range. It has been used in a wide range of biophysical and molecular biological experiments, including the measurement of molecular forces, characterization of conformational dynamics of biomolecules, observation of intracellular colocalization of proteins, and determination of receptor-ligand interaction times. In a widefield microscopy configuration, experiments are typically performed using surface-immobilized probes. Here, a method combining single-molecule tracking with alternating excitation (ALEX) smFRET experiments is presented, permitting the acquisition of smFRET time traces of surface-bound, yet mobile probes in plasma membranes or glass-supported lipid bilayers. For the analysis of recorded data, an automated, open-source software collection was developed supporting (i) the localization of fluorescent signals, (ii) single-particle tracking, (iii) determination of FRET-related quantities including correction factors, (iv) stringent verification of smFRET traces, and (v) intuitive presentation of the results. The generated data can conveniently be used as input for further exploration via specialized software, e.g., for the assessment of the diffusional behavior of probes or the investigation of FRET transitions.

This article presents a method for spatiotemporal analysis of mobile, single-molecule F&#246;rster resonance energy transfer (smFRET)-based probes using widefield fluorescence microscopy. The newly developed software toolkit allows the determination of smFRET time traces of moving probes, including the correct FRET efficiency and the molecular positions, as functions of time.

Single-molecule F&#246;rster resonance energy transfer (smFRET) is a versatile technique reporting on distances in the sub-nanometer to nanometer range. ...

G Protein-selective GPCR Conformations Measured Using FRET Sensors in a Live Cell Suspension Fluorometer Assay

F&#1255;rster resonance energy transfer (FRET)-based studies have become increasingly common in the investigation of GPCR signaling. Our research group developed an intra-molecular FRET sensor to detect the interaction between G&#945; subunits and GPCRs in live cells following agonist stimulation. Here, we detail the protocol for detecting changes in FRET between the &#946;2-adrenergic receptor and the G&#945;s C-terminus peptide upon treatment with 100 &#181;M isoproterenol hydrochloride as previously characterized1. Our FRET sensor is a single polypeptide consisting serially of a full-length GPCR, a FRET acceptor fluorophore (mCitrine), an ER/K SPASM (systematic protein affinity strength modulation) linker, a FRET donor fluorophore (mCerulean), and a G&#945; C-terminal peptide. This protocol will detail cell preparation, transfection conditions, equipment setup, assay execution, and data analysis. This experimental design detects small changes in FRET indicative of protein-protein interactions, and can also be used to compare the strength of interaction across ligands and GPCR-G protein pairings. To enhance the signal-to-noise in our measurements, this protocol requires heightened precision in all steps, and is presented here to enable reproducible execution.

Simple methods to detect the selective activation of G proteins by G protein-coupled receptors remain an outstanding challenge in cell signaling. Here, F&#1255;rster resonance energy transfer (FRET) biosensors have been developed by pairwise tethering a GPCR to G protein peptides to probe conformational changes at controlled concentrations in live cells.

F&#1255;rster resonance energy transfer (FRET)-based studies have become increasingly common in the investigation of GPCR signaling. Our research group ...

Visualizing the Conformational Dynamics of Membrane Receptors Using Single-Molecule FRET

Summary

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Chapters in this video

High Precision FRET at Single-molecule Level for Biomolecule Structure Determination

Using Three-color Single-molecule FRET to Study the Correlation of Protein Interactions

High-resolution Spatiotemporal Analysis of Receptor Dynamics by Single-molecule Fluorescence Microscopy

Measuring TCR-pMHC Binding In Situ using a FRET-based Microscopy Assay

Examining the Conformational Dynamics of Membrane Proteins in situ with Site-directed Fluorescence Labeling

Visualizing Intracellular SNARE Trafficking by Fluorescence Lifetime Imaging Microscopy

Single-Molecule FRET Imaging for Observing the Conformational Dynamics of Dynamin-Like GTPase Atlastin

FRET Microscopy for Real-time Monitoring of Signaling Events in Live Cells Using Unimolecular Biosensors

Automated Two-dimensional Spatiotemporal Analysis of Mobile Single-molecule FRET Probes

G Protein-selective GPCR Conformations Measured Using FRET Sensors in a Live Cell Suspension Fluorometer Assay