We thank the Microscopy Imaging Facility and Visual Function and Morphology Core at West Virginia University for discussion and help with image analysis. This work is supported by the tenure-track startup funds from West Virginia University School of Medicine to R.L. This work is also supported by National Institute of General Medical Sciences (NIGMS) Visual Sciences Center of Biomedical Research Excellence (Vs-CoBRE) (P20GM144230), and the NIGMS West Virginia Network of Biomedical Research Excellence (WV-INBRE) (P20GM103434).

Recombinant Human Myosin-7a Production and Functional Characterization Protocol

The authors declare no conflict of interest.

Presented here is a detailed protocol for the production of recombinant human myosin-7a protein from insect cells. Although the Sf9/baculovirus system has been used to produce a variety of myosins40,41,42,43, only recently has the mammalian myosin-7a been successfully purified using the MultiBac baculovirus system14. Mammalian myosin-7a is found to associate with three types of light chains, all of which are essential for the protein&#39;s structural and functional integrity14. This is in contrast to its invertebrate homolog and most other myosins, which typically bind to only one or two light chain types44,45. This means that to synthesize the human myosin-7a holoenzyme, at least four different genes must be expressed simultaneously in each Sf9 cell. In this case, the MultiBac system offers significant benefits over co-infection with multiple baculoviruses because it ensures reproducible ratios of the myosin-7a complex subunits in each infected cell. In fact, Belyaev et al. have statistically demonstrated this: as the number of virus types increases, the likelihood of cells receiving an equal virus ratio decreases dramatically46. For example, with two virus types, only 12.78% of cells achieve an equal ratio, while this percentage drops to 0.29% when four virus types are used, assuming each virus type is distributed between cells independently. This variability can be problematic when the subunit proteins need to assemble at a consistent ratio to produce the maximum yield of the complex. While this paper focuses on mammalian myosin-7a, it is increasingly evident that the MultiBac system offers a more optimized approach for producing multimeric complexes than the co-infection method, particularly for proteins with more subunits and produced in low yields.
Several factors are critical for achieving high-yield production of myosin-7a protein using this method. First, it is crucial to determine the optimal timing for harvesting Sf9 cells. This allows maximum protein production while minimizing the detrimental effects of cell lysis and death caused by the virus. MultiBac-based protein complex production often exhibits a delayed peak in expression compared to monocistronic baculovirus systems or when expressing smaller proteins. We found that the best time to harvest cells infected with the myosin-7a MultiBac virus is between 60 - 65 h post-infection. Continuous monitoring of protein expression levels throughout the process is strongly recommended. This can be accomplished using fluorescent microscopy if a fluorescent protein tag is fused or through SDS-PAGE analysis otherwise. Additionally, it is important to monitor cell viability concurrently to identify the optimal timing for achieving the highest protein yield with minimal cell death.
Myosin-7a is a large monomeric myosin susceptible to protein degradation14. To prevent degradation during the purification process, it is important to ensure that all buffers are pre-chilled and all procedures are conducted at 4 &#730;C. In addition, minimizing the exposure of myosin-7a to proteases is critical. Besides utilizing protease inhibitor cocktails, we recommend keeping the incubation of the cell lysate with FLAG-resin to just 1 h. Extending this duration has not been shown to significantly improve resin binding or increase total protein yield and may pose a higher risk of protein degradation.
A distinctive feature of mammalian myosin-7a, compared to isoforms from lower species44, is its combination of unique light chain components. These light chains play important regulatory roles in the function of myosin-7a. For instance, calmodulin dynamically interacts with the myosin-heavy chain in a Ca2+-dependent manner47, modulating its motility and mechanical output, a mechanism that seems specifically adapted to the mammalian auditory hair cells14. While the exact binding affinities of calmodulin to individual IQ motifs have yet to be determined in the context of the whole molecule, we have observed that some calmodulin gradually dissociates as the excess light chains in the cell lysate are removed during purification. This may alter the mechanical properties of myosin-7a. To mitigate this, we employ spin columns combined with gentle centrifugation for the elution step. This allows proteins to be eluted in a small volume and at a high concentration, which can obviate the need for concentration steps. This practice shortens the total protein purification process and minimizes the risk of light chain dissociation. In actin gliding assays, we include excess light chain proteins in the final buffer to ensure that the native light chains remain bound with the myosin-7a heavy chain.
The requirement for excess light chains represents one of several differences between the actin gliding assay with myosin-7a and that of other well-studied myosins such as myosin-2. Myosin-2 assays are typically performed at low ionic strength (e.g., 50 mM). As ionic strength is raised towards physiological (150 mM), actin filaments tend to detach, and motility slows. In the case of myosin-7a, motility is stalled at low ionic strength, and gliding is only observed at greater than or equal to 150 mM. Due to the autoinhibition of full-length myosin-7a, it is applied to the coverslip in a high ionic strength solution in a manner akin to how myosin filaments are dissolved before application to allow proteins to bind in an orientation and conformation that allows subsequent gliding.
The low velocity observed in actin gliding assays with myosin-7a introduces some challenges in acquiring and analyzing motility data. Indeed, the translocation is several orders of magnitude slower compared to skeletal muscle myosin, which was used when this assay was originally developed30. This low velocity can lead to difficulty in accurate measurement and an overestimation of velocity that scales with frame rate48. The localization precision of any tracking method is finite, and even a static object has an apparent shift in position between successive images. As the sampling rate increases, this leads to an artificially high value for velocity. This effect is true for any type of motility assay, but the relative effect is very small for assays where a large movement of several pixels occurs between frames. By taking data points at very long intervals (every 60 s, 90 s, etc.), it can be verified that the measured velocity is accurate since the value should be unaffected by the sampling rate. Since the recording interval for myosin-7a is so long, the delay can be taken advantage of to record from several positions during the same acquisition. This effectively allows for the recording of several movies at one time. A disadvantage of this method is that mechanical imperfections with the stage will lead to additional drift due to the switching of positions. This can be accounted for using image stabilization as described above.
In the original Python2 version of the FAST software (github.com/turalaksel/FASTrack), each output data point represents a velocity for a filament within an N-frame window (5 frames by default). A modified Python3 version of the software (github.com/NeilBillington/FASTrack3) includes an additional output in which data points are on a filament-by-filament basis. The default plots produced by the software are based on the N window-type dataset. Both output types are equally valid, and although the original output will produce many more data points per movie, we typically use the filament-based data since this is more directly comparable to existing methods for quantifying filament gliding and yields more intuitive information about the numbers of filaments with specific velocities in a particular movie. Note that even in this filament-type analysis, the number of data points will not correspond exactly to the true number of filaments since tracking stops when filaments cross paths, and new tracks are then detected as they emerge after crossing.
Limitations of the methods described in this paper are that mammalian protein is being expressed in insect cells. Although many such proteins, including this one, have been successfully expressed in this way, there are other expression systems that may more closely mimic the native environment of the protein. Mammalian expression systems could introduce important post-translational modifications to the protein which are absent in the insect system. The same is true to an even greater extent for expression in a bacterial system, as used here for producing myosin light chains. Nevertheless, we believe the relative simplicity and high yield in these cases outweigh the potential limitations. The in vitro motility assay that is used to characterize the protein is limited in how much information it can yield about the protein. For example, many aspects of myosin regulation are masked or circumvented by the assay and thus cannot be investigated using this technique. Many other assay types, such as single-molecule motility, optical trapping, and biochemical and biophysical techniques, exist to investigate the properties of myosin in vitro, but the filament gliding assay is chosen here as a method to measure myosin activity because it requires less protein than many biochemical assays, is simple to perform and where successful motility can be demonstrated, tells us that the protein is both biochemically and mechanically active.
The workflow described here represents a series of methods for producing high-quality myosin-7a protein and characterizing its mechanical properties. Although these methods are specifically tailored to this myosin class, the expression and purification procedures are more generally useful as a guideline for how to produce this type of labile protein, consisting of several distinct polypeptides and with a tendency for dissociation and degradation. In addition, the characterization methods are useful for all types of motor proteins, and in particular, the considerations of data acquisition and analysis parameters are intended to be useful for anyone measuring the translocation rate of low-velocity molecular motors.

Myosins are molecular motor proteins that interact with actin to drive numerous cellular processes1,2,3,4. Humans possess 12 classes and 39 myosin genes5, which are involved in a wide range of physiological functions, such as muscle contraction6 and sensory processes7. Each myosin molecule is a multimeric complex composed of a heavy chain and light chains. The heavy chain is divided into head, neck, and tail regions. The head contains actin- and nucleotide-binding sites that are responsible for ATP hydrolysis and generating force on actin filaments2. The neck is formed by several &#945;-helical IQ motifs where a specific set of light chains are bound. They together function as a lever arm to amplify the motor&#39;s conformational changes into large movements8,9,10. The tail contains class-specific subdomains and plays a regulatory role in tuning myosin&#39;s motor activity and mediating interactions with cellular binding partners2,11.
Human myosin-7a, a member of class-7 myosins, is essential for auditory and visual processes12,13. The IQ motifs of human myosin-7a are associated with a unique combination of light chains, including the regulatory light chain (RLC), calmodulin, and calmodulin-like protein 4 (CALML4)14,15,16. Besides stabilizing the lever arm, these light chains regulate the mechanical properties of myosin-7a in response to calcium signaling, a feature that appears to be unique to the mammalian isoform14.
Defects in the gene encoding the myosin-7a heavy chain (MYO7A/USH1B) are responsible for Usher syndrome type 1, the most severe form of combined vision and hearing loss in humans17. Additionally, the light chain gene CALML4, is among the candidate genes mapped to contain the causative allele for USH1H, another variant of type 1 Usher syndrome15,18. In the retina, myosin-7a is expressed in the retinal pigment epithelium and photoreceptor cells13. It has been implicated in the localization of melanosomes in the retinal pigment epithelium (RPE)19 and phagocytosis of photoreceptor outer segment disks by the RPE cells20. In the inner ear, myosin-7a is primarily found in the stereocilia, where it plays a critical role in establishing hair bundles and in gating the mechano-electrical transduction process12,21,22.
While the importance of myosin-7a in sensory cells is well established, its functional mechanisms at the molecular level remain poorly understood. This gap in knowledge is partly due to the challenges in purifying the intact protein, especially the mammalian isoform. Recently, significant progress has been made using the MultiBac system to recombinantly express the complete human myosin-7a holoenzyme14. This advancement has enabled structural and biophysical characterizations of this motor protein, leading to the discovery of several unique properties of human myosin-7a that are specifically adapted for mammalian auditory functions14,23.
The MultiBac system is an advanced baculovirus/insect cell platform specifically designed for the expression of eukaryotic multimeric complexes24,25. A key feature of this system is its ability to host multiple gene expression cassettes, each encoding a subunit of the complex, within a single MultiBac baculovirus. The assembly of the multigene expression cassettes is facilitated through a so-called multiplication module: a homing endonuclease (HE) site and a matching designed BstXI site flanking the multiple cloning sites (MCS). This module enables the iterative assembly of a single expression cassette by restriction/ligation, leveraging the fact that the HE and BstXI restriction sites are eliminated upon their ligation. In this paper, human myosin-7a heavy chain, RLC, calmodulin, and CALML4 are each cloned into the multiplication module within the pACEBac1 vector (Figure 1A), which are then assembled into a multigene expression cassette through the iterative process (Figure 1B). The myosin-7a multigene cassette is integrated into the baculoviral genome (bacmid) through the transposition of the mini-Tn7 element from the pACEBac1 vector to the mini-attTn7 target site in the genome (Figure 1C). Following procedures for bacmid purification, baculovirus production, and amplification (Figure 1D,E), the recombinant myosin-7a MultiBac baculovirus is prepared and can be used for large-scale protein production (Figure 1F). Additionally, the myosin-7a light chains can be produced separately in E. coli and purified using a cleavable His6-SUMO tag26,27,28. The purified light chains are useful for studying their binding dynamics and regulation of myosin-7a.
The purified myosin-7a protein can be subjected to structural, biochemical, and biophysical studies to gain insights into the structural-functional regulation of this motor protein. Additionally, its interactions with the actin network and other binding proteins29 can be examined using a variety of in vitro reconstitution approaches. Findings from these analyses will inform the biophysical properties of this myosin, leading to a mechanistic understanding of how myosin-7a drives the cytoskeletal changes and ultimately shapes the unique morphology and function of sensory cells. In this paper, we detail a workflow for actin filament gliding assay that has been specifically adapted for mammalian myosin-7a. Actin filament gliding assay is a robust in vitro motility assay that quantitatively studies the movement of fluorescent actin filaments propelled by a large number of myosin motors immobilized on a coverslip surface30,31,32. The advantages of this assay include its simplicity of setup, minimal equipment requirements (a wide-field fluorescence microscope equipped with a digital camera), and high reproducibility. Additionally, because the motion of actin filaments is driven by a cluster of immobilized myosin motors, this assay is particularly useful for studying the motility of monomeric myosins such as myosin-7a14,33. The protocols include several modifications, from experimental procedures to imaging analysis, specifically tailored to the unique motile properties of mammalian myosin-7a. With the availability of intact myosin-7a protein and the functional characterization protocol outlined here, this paper lays the groundwork for further investigation into the molecular roles of myosin-7a in both physiological and pathological processes.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1.7 mL microcentrifuge tubes</td>
			<td>VWR</td>
			<td>87003-294</td>
			<td></td>
		</tr>
		<tr>
			<td>1X FLAG Peptide</td>
			<td>GenScript</td>
			<td>N/A</td>
			<td>Custom peptide synthesis</td>
		</tr>
		<tr>
			<td>22x22mm No. 1.5 coverslips</td>
			<td>VWR</td>
			<td>48366-227</td>
			<td></td>
		</tr>
		<tr>
			<td>250 mL Conical Centrifuge Tubes</td>
			<td>Nunc</td>
			<td>376814</td>
			<td></td>
		</tr>
		<tr>
			<td>250 mL Vented Erlenmyer Shaker Flask</td>
			<td>IntelixBio</td>
			<td>DBJ-SF250VP</td>
			<td></td>
		</tr>
		<tr>
			<td>2-Mercaptoethanol</td>
			<td>VWR</td>
			<td>M131</td>
			<td></td>
		</tr>
		<tr>
			<td>75x25x1 mm Vistavision microscope slides</td>
			<td>VWR</td>
			<td>16004-42</td>
			<td></td>
		</tr>
		<tr>
			<td>Actin Protein (&#62;99% Pure)</td>
			<td>Cytoskeleton</td>
			<td>AKL99</td>
			<td></td>
		</tr>
		<tr>
			<td>Amicon Ultra-0.5 Centrifugal Filter Unit</td>
			<td>Millipore Sigma</td>
			<td>UFC510024</td>
			<td></td>
		</tr>
		<tr>
			<td>Amicon Ultra-4 Centrifugal Filter Unit</td>
			<td>Millipore Sigma</td>
			<td>UFC801024</td>
			<td></td>
		</tr>
		<tr>
			<td>ANTI-FLAG M2 Affinity Gel</td>
			<td>Millipore Sigma</td>
			<td>A2220</td>
			<td></td>
		</tr>
		<tr>
			<td>ATP</td>
			<td>Millipore Sigma</td>
			<td>A7699</td>
			<td></td>
		</tr>
		<tr>
			<td>ATP</td>
			<td>Millipore Sigma</td>
			<td>A7699</td>
			<td></td>
		</tr>
		<tr>
			<td>Bio-Spin Disposable Chromatography Column</td>
			<td>Bio-Rad</td>
			<td>732-6008</td>
			<td></td>
		</tr>
		<tr>
			<td>BL21 Competent E. coli</td>
			<td>New England Biolabs</td>
			<td>C2530H</td>
			<td></td>
		</tr>
		<tr>
			<td>Bluo-Gal</td>
			<td>Thermo Fisher</td>
			<td>15519028</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin</td>
			<td>Millipore Sigma</td>
			<td>5470</td>
			<td></td>
		</tr>
		<tr>
			<td>BstXI Enzyme</td>
			<td>New England Biolabs</td>
			<td>R0113S</td>
			<td></td>
		</tr>
		<tr>
			<td>Calmodulin</td>
			<td>Millipore Sigma</td>
			<td>208694</td>
			<td></td>
		</tr>
		<tr>
			<td>Catalase</td>
			<td>Millipore Sigma</td>
			<td>C40</td>
			<td></td>
		</tr>
		<tr>
			<td>Champion pET-SUMO Expression System</td>
			<td>Thermo Fisher</td>
			<td>K30001</td>
			<td></td>
		</tr>
		<tr>
			<td>cOmplete, EDTA-free Protease Inhibitor Cocktail</td>
			<td>Roche Diagnostics</td>
			<td>5056489001</td>
			<td></td>
		</tr>
		<tr>
			<td>Cutsmart Buffer</td>
			<td>New England Biolabs</td>
			<td>B6004S</td>
			<td></td>
		</tr>
		<tr>
			<td>DL-Dithiothreitol</td>
			<td>Millipore Sigma</td>
			<td>DO632</td>
			<td></td>
		</tr>
		<tr>
			<td>DL-Dithiothreitol</td>
			<td>Millipore Sigma</td>
			<td>DO632</td>
			<td></td>
		</tr>
		<tr>
			<td>DNase I, Spectrum Chemical</td>
			<td>Fisher Scientific</td>
			<td>18-610-304</td>
			<td></td>
		</tr>
		<tr>
			<td>Double-Sided Tape</td>
			<td>Office Depot</td>
			<td>909955</td>
			<td></td>
		</tr>
		<tr>
			<td>EGTA, Molecular Biology Grade</td>
			<td>Millipore Sigma</td>
			<td>324626-25GM</td>
			<td></td>
		</tr>
		<tr>
			<td>EGTA, Molecular Biology Grade</td>
			<td>Millipore Sigma</td>
			<td>324626-25GM</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Thermo Fisher</td>
			<td>BP2818</td>
			<td></td>
		</tr>
		<tr>
			<td>ExpiFectamine Sf Transfection Reagent</td>
			<td>Gibco</td>
			<td>A38915</td>
			<td></td>
		</tr>
		<tr>
			<td>FAST program</td>
			<td>http://spudlab.stanford.edu/fast-for-automatic-motility-measurements;&#160;</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Fisherbrand&#160;Model 505 Sonic Dismembrator</td>
			<td>Fisher Scientific</td>
			<td>FB505110</td>
			<td></td>
		</tr>
		<tr>
			<td>Gentamicin Reagent Solution</td>
			<td>Gibco</td>
			<td>15710-064</td>
			<td>10 mg/mL in distilled water</td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Millipore Sigma</td>
			<td>G5767</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose Oxidase</td>
			<td>Millipore Sigma</td>
			<td>G2133</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Invitrogen</td>
			<td>15514-011</td>
			<td></td>
		</tr>
		<tr>
			<td>HisPur Cobalt Resin</td>
			<td>Thermo Fisher</td>
			<td>89966</td>
			<td></td>
		</tr>
		<tr>
			<td>I-CeuI Enzyme</td>
			<td>New England Biolabs</td>
			<td>R0699S</td>
			<td></td>
		</tr>
		<tr>
			<td>Image Stabilizer Plugin</td>
			<td>https://www.cs.cmu.edu/~kangli/code/Image_Stabilizer.html</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ImageJ FIJI</td>
			<td>https://imagej.net/Fiji/Downloads</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Imidazole</td>
			<td>Millipore Sigma</td>
			<td>I2399</td>
			<td></td>
		</tr>
		<tr>
			<td>In-Fusion Snap Assembly Master Mix</td>
			<td>TaKaRa</td>
			<td>638948</td>
			<td></td>
		</tr>
		<tr>
			<td>IPTG</td>
			<td>Thermo Fisher</td>
			<td>15529019</td>
			<td></td>
		</tr>
		<tr>
			<td>Isopropanol</td>
			<td>Fisher Scientific</td>
			<td>A451SK</td>
			<td></td>
		</tr>
		<tr>
			<td>Kanamycin</td>
			<td>Fisher Scientific</td>
			<td>AAJ67354AD</td>
			<td></td>
		</tr>
		<tr>
			<td>Large Orifice Pipet Tips</td>
			<td>Fisher Scientific</td>
			<td>02-707-134</td>
			<td>1-200uL</td>
		</tr>
		<tr>
			<td>LB Agar, Ready-Made Powder</td>
			<td>Thermo Fisher</td>
			<td>J75851-A1</td>
			<td></td>
		</tr>
		<tr>
			<td>Leupeptin Protease Inhibitor</td>
			<td>Thermo Fisher</td>
			<td>78435</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium chloride</td>
			<td>Thermo Fisher</td>
			<td>J61014.=E</td>
			<td>1M</td>
		</tr>
		<tr>
			<td>Magnesium chloride</td>
			<td>Thermo Fisher</td>
			<td>J61014.=E</td>
			<td>1M</td>
		</tr>
		<tr>
			<td>Max Efficiency DH10Bac Competent Cells</td>
			<td>Gibco</td>
			<td>10361012</td>
			<td></td>
		</tr>
		<tr>
			<td>Microcentrifuge Tubes, 1.7mL</td>
			<td>VWR</td>
			<td>87003-294</td>
			<td></td>
		</tr>
		<tr>
			<td>Microcentrifuge Tubes, 1.7mL</td>
			<td>VWR</td>
			<td>87003-294</td>
			<td></td>
		</tr>
		<tr>
			<td>Microcentrifuge Tubes, 1.7mL</td>
			<td>VWR</td>
			<td>87003-294</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope</td>
			<td>Nikon</td>
			<td>Model: Eclipse Ti with H-TIRF system with 100X TIRF objective</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope Camera</td>
			<td>ORCA-Fusion BT</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope Laser Unit</td>
			<td>Andor iXon Ultra</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Miller&#39;s LB Broth</td>
			<td>Corning</td>
			<td>46-050-CM</td>
			<td></td>
		</tr>
		<tr>
			<td>MOPS</td>
			<td>Millipore Sigma</td>
			<td>M3183</td>
			<td></td>
		</tr>
		<tr>
			<td>MOPS</td>
			<td>Millipore Sigma</td>
			<td>M3183</td>
			<td></td>
		</tr>
		<tr>
			<td>NanoDrop One/OneC Microvolume UV-Vis Spectrophotometer</td>
			<td>Thermo Fisher</td>
			<td>ND-ONE-W</td>
			<td></td>
		</tr>
		<tr>
			<td>NanoDrop One/OneC Microvolume UV-Vis Spectrophotometer</td>
			<td>Thermo Fisher</td>
			<td>ND-ONE-W</td>
			<td></td>
		</tr>
		<tr>
			<td>NEB 5-alpha Competent E.coli (High Efficiency)</td>
			<td>New England Biolabs</td>
			<td>C2987H</td>
			<td></td>
		</tr>
		<tr>
			<td>NEBuffer r3.1</td>
			<td>New England Biolabs</td>
			<td>B6003S</td>
			<td></td>
		</tr>
		<tr>
			<td>NIS Elements</td>
			<td>Nikon</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>NIS-Elements</td>
			<td>Nikon</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Nitrocellulose</td>
			<td>LADD Research Industries</td>
			<td>53152</td>
			<td></td>
		</tr>
		<tr>
			<td>Opti-MEM I Reduced Serum Medium</td>
			<td>Gibco</td>
			<td>31985070</td>
			<td></td>
		</tr>
		<tr>
			<td>pACEBac1 Vector</td>
			<td>Geneva Biotech</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Parafilm</td>
			<td>Millipore Sigma</td>
			<td>P7793</td>
			<td></td>
		</tr>
		<tr>
			<td>PMSF</td>
			<td>Millipore Sigma</td>
			<td>78830</td>
			<td></td>
		</tr>
		<tr>
			<td>PureLink RNase A (20 mg/mL)</td>
			<td>Invitrogen</td>
			<td>12091021</td>
			<td></td>
		</tr>
		<tr>
			<td>QIAprep Spin Miniprep Kit (250)</td>
			<td>QIAGEN</td>
			<td>27106</td>
			<td></td>
		</tr>
		<tr>
			<td>QIAquick Gel Extraction Kit (50)</td>
			<td>QIAGEN</td>
			<td>28704</td>
			<td></td>
		</tr>
		<tr>
			<td>QIAquick PCR Purification Kit (50)</td>
			<td>QIAGEN</td>
			<td>28104</td>
			<td></td>
		</tr>
		<tr>
			<td>Quick CIP</td>
			<td>New England Biolabs</td>
			<td>M0525S</td>
			<td></td>
		</tr>
		<tr>
			<td>Rhodamine phalloidin</td>
			<td>Invitrogen</td>
			<td>R415</td>
			<td></td>
		</tr>
		<tr>
			<td>S.O.C. Medium</td>
			<td>Invitrogen</td>
			<td>15544034</td>
			<td></td>
		</tr>
		<tr>
			<td>SENP2 protease</td>
			<td></td>
			<td>PMID:17591783</td>
			<td>Purified in the lab</td>
		</tr>
		<tr>
			<td>Sf9 cells</td>
			<td>Thermo Fisher</td>
			<td>11496015</td>
			<td></td>
		</tr>
		<tr>
			<td>Sf-900 III SFM (1X) - Serum Free Media Complete</td>
			<td>Gibco</td>
			<td>12658-027</td>
			<td></td>
		</tr>
		<tr>
			<td>Slide-A-Lyzer G3 Dialysis Cassettes, 10K MWCO, 3 mL</td>
			<td>Thermo Fisher</td>
			<td>A52971</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>Millipore Sigma</td>
			<td>S7653</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>Millipore Sigma</td>
			<td>S7653</td>
			<td></td>
		</tr>
		<tr>
			<td>Stericup Quick Release Vacuum Driven Disposable Filtration System</td>
			<td>Millipore Sigma</td>
			<td>S2GPU01RE</td>
			<td></td>
		</tr>
		<tr>
			<td>Superdex 75 Increase 10/300 GL</td>
			<td>Cytiva</td>
			<td>29148721</td>
			<td></td>
		</tr>
		<tr>
			<td>T4 DNA Ligase</td>
			<td>New England Biolabs</td>
			<td>M0202S</td>
			<td></td>
		</tr>
		<tr>
			<td>T4 DNA Ligase Buffer - 10X with 10mM ATP</td>
			<td>New England Biolabs</td>
			<td>B0202A</td>
			<td></td>
		</tr>
		<tr>
			<td>Tetracycline Hydrochloride</td>
			<td>Millipore Sigma</td>
			<td>T7660-5G</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris</td>
			<td>Millipore Sigma</td>
			<td>10708976001</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X</td>
			<td>American Bioanalytical</td>
			<td>9002-93-1</td>
			<td></td>
		</tr>
	</tbody>
</table>

multibac system-based purification and biophysical characterization of human myosin-7a

Myosin-7a is an actin-based motor protein vital for auditory and visual processes. Mutations in myosin-7a lead to Usher syndrome type 1, the most common and severe form of deaf-blindness in humans. It is hypothesized that myosin-7a forms a transmembrane adhesion complex with other Usher proteins, essential for the structural-functional integrity of photoreceptor and cochlear hair cells. However, due to the challenges in obtaining pure, intact protein, the exact functional mechanisms of human myosin-7a remain elusive, with limited structural and biomechanical studies available. Recent studies have shown that mammalian myosin-7a is a multimeric motor complex consisting of a heavy chain and three types of light chains: regulatory light chain (RLC), calmodulin, and calmodulin-like protein 4 (CALML4). Unlike calmodulin, CALML4 does not bind to calcium ions. Both the calcium-sensitive, and insensitive calmodulins are critical for mammalian myosin-7a for proper fine-tuning of its mechanical properties. Here, we describe a detailed method to produce recombinant human myosin-7a holoenzyme using the MultiBac Baculovirus protein expression system. This yields milligram quantities of high-purity full-length protein, allowing for its biochemical and biophysical characterization. We further present a protocol for assessing its mechanical and motile properties using tailored in vitro motility assays and fluorescence microscopy. The availability of the intact human myosin-7a protein, along with the detailed functional characterization protocol described here, paves the way for further investigations into the molecular aspects of myosin-7a in vision and hearing.

The purified myosin-7a complex and light chain proteins can be evaluated by SDS-PAGE gel electrophoresis, as shown in Figure 3. The band above the 200 kDa marker corresponds to the myosin-7a heavy chain (255 kDa). The three bands migrating between the 22 and 14 kDa markers from top to bottom are RLC (20 kDa), calmodulin, and CALML4, respectively. While calmodulin and CALML4 have a similar molecular weight of approximately 17 kDa, the two proteins can be separated using a 16% Tris-Glycine gel.
Video 1 and Figure 5 demonstrate a characteristic actin filament gliding assay with mammalian myosin-7a. An immediate feature revealed by this assay is the slow motility of myosin-7a. The video is played back at 500 times normal speed to better visualize the movement of actin filaments driven by this myosin. This assay can be modified to further study how external factors such as temperature, ionic strength, and solution viscosity influence the activity of myosin-7a. Additionally, myosin-7a binding proteins can be introduced into the flow cell to investigate their effects on actomyosin interactions and motility.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/67135/67135fig01.jpg" /> 
Figure 1: Workflow for MultiBac-system-based myosin-7a holoenzyme production. (A) Insert the cDNAs encoding the myosin-7a heavy chain, RLC, CALML4, and calmodulin into the multiple cloning sites (MCS) of the pACEBac1 vector. (B) Construct the multigene expression cassette for encoding the myosin-7a complex by iteratively ligating the pACEBac1 vectors that contain the cDNAs of the myosin-7a heavy chain, RLC, CALML4, and calmodulin. (C) Integrate the myosin-7a multigene cassette into the baculovirus genome through the transposition of the mini-Tn7 element from the pACEBac1 vector to the mini-attTn7 target site in the genome. (D) Produce baculoviruses expressing the myosin-7a complex by transfecting Sf9 cells with the recombinant bacmid containing the myosin-7a multigene cassette. (E) The baculovirus can be amplified by inoculating the P0 virus into an Sf9 cell suspension culture and collecting the supernatant. The resulting product, the P1 virus, can be used for large-scale protein expression. (F) Workflow for the FLAG-affinity column-based purification of the myosin-7a complex. <a href="https://www.jove.com/files/ftp_upload/67135/67135fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/67135/67135fig02.jpg" /> 
Figure 2: Representative fluorescent images of Sf9 cells transfected with bacmid expressing myosin-7a with a C-terminal GFP tag. The images show the normal progression of baculovirus infection: cells begin to express myosin-7a around day 4 post-transfection, with nearly all cells becoming infected within one week. <a href="https://www.jove.com/files/ftp_upload/67135/67135fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/67135/67135fig03.jpg" /> 
Figure 3: SDS-gels of purified myosin-7a complex and light chain proteins. (A)&#160;Purified full-length human myosin-7a holoenzyme using the MultiBac system. The heavy chain (HC) and light chains are indicated. (B) Purified RLC and CALML4 using the His6-SUMO system. Calmodulin (CaM) is purchased (see Table of Materials) and purified from the Bovine brain. <a href="https://www.jove.com/files/ftp_upload/67135/67135fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/67135/67135fig04.jpg" /> 
Figure 4: Workflow for flow chamber assembly and actin gliding assays. A nitrocellulose-treated coverslip is attached to a microscope slide using two pieces of double-sided tape. This creates a flow chamber with a volume of approximately 10 &#181;L. Proteins are added sequentially to the chamber, while excess solutions are wicked through the channel using tissue paper. <a href="https://www.jove.com/files/ftp_upload/67135/67135fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/67135/67135fig05.jpg" /> 
Figure 5: Representative results of gliding actin filament assays and the tracking analysis. (A)&#160;Example frame from a timelapse recording showing actin filament movement driven by surface-decorated myosin-7a motors. (B) Filament tracking image output from the FAST program for the same field-of-view as shown in (A). (C) Representative histogram of the actin gliding velocity generated by mammalian myosin-7a: 4.2 &#177; 1.4 nm/s (mean &#177; standard deviation; the number of tracks = 550). (D) Example of autogenerated output from the FAST program showing the calculated filament length and velocities. %STUCK shows the percentage of filaments that are deemed to be stuck based on the user supplied minimum velocity cutoff. MVEL represents the mean velocity of all non-stuck filaments. <a href="https://www.jove.com/files/ftp_upload/67135/67135fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Video 1: Actin filament gliding assay performed with myosin-7a. Purified full-length human myosin-7a is attached to the surface. This movie was acquired at 1 frame every 30 s with 200 ms exposure. <a href="https://www.jove.com/files/ftp_upload/67135/JOVE_Video1_New.mp4" target="_blank">Please click here to download this Video.</a>

Author Spotlight: Unraveling the Role of Myosin-7a and Usher Proteins in Hearing and Human Disease

This protocol details the procedures for recombinantly producing the human myosin-7a holoenzyme using the MultiBac Baculovirus system and for studying its motility using a tailored in vitro filament gliding assay.

MultiBac System-Based Purification and Biophysical Characterization of Human Myosin-7a

Myosin-7a is an actin-based motor protein vital for auditory and visual processes. Mutations in myosin-7a lead to Usher syndrome type 1, the most common ...

multibac-system-based-purification-biophysical-characterization-human

Nanyang Technological University

Research

JoVE Journal

Biochemistry

361 Views.  West Virginia University. This protocol details the procedures for recombinantly producing the human myosin-7a holoenzyme using the MultiBac Baculovirus system and for studying its motility using a tailored in vitro filament gliding assay. 

Video: Author Spotlight: Unraveling the Role of Myosin-7a and Usher Proteins in Hearing and Human Disease

Characterization of Multi-subunit Protein Complexes of Human MxA Using Non-denaturing Polyacrylamide Gel-electrophoresis

The formation of oligomeric complexes is a crucial prerequisite for the proper structure and function of many proteins. The interferon-induced antiviral effector protein MxA exerts a broad antiviral activity against many viruses. MxA is a dynamin-like GTPase and has the capacity to form oligomeric structures of higher order. However, whether oligomerization of MxA is required for its antiviral activity is an issue of debate. We describe here a simple protocol to assess the oligomeric state of endogenously or ectopically expressed MxA in the cytoplasmic fraction of human cell lines by non-denaturing polyacrylamide gel electrophoresis (PAGE) in combination with Western blot analysis. A critical step of the protocol is the choice of detergents to prevent aggregation and/or precipitation of proteins particularly associated with cellular membranes such as MxA, without interfering with its enzymatic activity. Another crucial aspect of the protocol is the irreversible protection of the free thiol groups of cysteine residues by iodoacetamide to prevent artificial interactions of the protein. This protocol is suitable for a simple assessment of the oligomeric state of MxA and furthermore allows a direct correlation of the antiviral activity of MxA interface mutants with their respective oligomeric states.

This article describes a simple and rapid protocol to evaluate the oligomeric state of the dynamin-like GTPase MxA protein from lysates of human cells using a combination of non-denaturing PAGE with western blot analysis.

The formation of oligomeric complexes is a crucial prerequisite for the proper structure and function of many proteins. The interferon-induced antiviral ...

Thermostabilization, Expression, Purification, and Crystallization of the Human Serotonin Transporter Bound to S-citalopram

The serotonin transporter is a sodium and chloride-coupled transporter that &#34;pumps&#34; extracellular serotonin into cells. S-citalopram is a drug used to treat depression and anxiety by binding to the serotonin transporter with high-affinity, blocking serotonin reuptake. Here we report an efficient procedure and a set of tools to stabilize, express, purify, and crystallize serotonin transporter-antibody complexes bound to S-citalopram and other antidepressants. Mutations which stabilize the serotonin transporter were identified using an S-citalopram binding assay. Serotonin transporter expressed in baculovirus-transduced HEK293S GnTI- cells, was reconstituted into proteoliposomes and used to raise high-affinity antibodies. We have developed a strategy to discover antibodies that are useful for structural studies. A straightforward approach for the expression of antibody fragments in Sf9 cells has also been established. Transporter-antibody complexes purified using this procedure are well-behaved and readily crystallize, producing complexes with S-citalopram that diffract X-rays to 3-4 &#197; resolution. The strategies developed here can be utilized to determine the structure of other challenging membrane proteins.

Thermostabilization, Expression, Purification, and Crystallization of the Human Serotonin Transporter Bound to S-citalopram

This manuscript describes how to screen for thermostabilizing mutations, purify the human serotonin transporter, generate high affinity antibodies, and crystallize the serotonin transporter-antibody complex bound to the antidepressant drug S-citalopram. This protocol can be adapted to the study of other challenging membrane transporters, receptors, and channels.

The serotonin transporter is a sodium and chloride-coupled transporter that &#34;pumps&#34; extracellular serotonin into cells. S-citalopram is a drug ...

Laboratory Scale Production and Purification of a Therapeutic Antibody

Ensuring the successful production of a therapeutic antibody begins early on in the development process. The first stage is vector expression of the antibody genes followed by stable transfection into a suitable cell line. The stable clones are subjected to screening in order to select those clones with desired production and growth characteristics. This is a critical albeit time-consuming step in the process. This protocol considers vector selection and sourcing of antibody sequences for the expression of a therapeutic antibody. The methods describe preparation of vector DNA for stable transfection of a suspension variant of human embryonic kidney 293 (HEK-293) cell line, using polyethylenimine (PEI). The cells are transfected as adherent cells in serum-containing media to maximize transfection efficiency, and afterwards adapted to serum-free conditions. Large scale production, setup as batch overgrow cultures is used to yield antibody protein that is purified by affinity chromatography using an automated fast protein liquid chromatography (FPLC) instrument. The antibody yields produced by this method can provide sufficient protein to begin initial characterization of the antibody. This may include in vitro assay development or physicochemical characterization to aid in the time-consuming task of clonal screening for lead candidates. This method can be transferable to the development of an expression system for the production of biosimilar antibodies.

This protocol describes the production of a therapeutic antibody in a mammalian expression system. The methods described include preparation of vector DNA, stable transfection and serum-free adaptation of a human embryonic kidney 293 cell line, set up of large scale cultures and purification using affinity chromatography.

Ensuring the successful production of a therapeutic antibody begins early on in the development process. The first stage is vector expression of the ...

Expression, Purification, and Antimicrobial Activity of S100A12

Calgranulin proteins are important mediators of innate immunity and are members of the S100 class of the EF-hand family of calcium binding proteins. Some S100 proteins have the capacity to bind transition metals with high affinity and effectively sequester them away from invading microbial pathogens in a process that is termed "nutritional immunity". S100A12 (EN-RAGE) binds both zinc and copper and is highly abundant in innate immune cells such as macrophages and neutrophils. We report a refined method for the expression, enrichment and purification of S100A12 in its active, metal-binding configuration. Utilization of this protein in bacterial growth and viability analyses reveals that S100A12 has antimicrobial activity against the bacterial pathogen, Helicobacter pylori. The antimicrobial activity is predicated on the zinc-binding activity of S100A12, which chelates nutrient zinc, thereby starving H. pylori which requires zinc for growth and proliferation.

Here, we present a method to express and purify S100A12 (calgranulin C). We describe a protocol to measure its antimicrobial activity against the human pathogen H. pylori.

Calgranulin proteins are important mediators of innate immunity and are members of the S100 class of the EF-hand family of calcium binding proteins. Some ...

Recombinant Protein Expression, Crystallization, and Biophysical Studies of a Bacillus-conserved Nucleotide Pyrophosphorylase, BcMazG

To overcome safety restrictions and regulations when studying genes and proteins from true pathogens, their homologues can be studied. Bacillus anthracis is an obligate pathogen that causes fatal inhalational anthrax. Bacillus cereus is considered a useful model for studying B. anthracis due to its close evolutionary relationship. The gene cluster ba1554 - ba1558 of B. anthracis is highly conserved with the bc1531- bc1535 cluster in B. cereus, as well as with the bt1364-bt1368 cluster in Bacillus thuringiensis, indicating the critical role of the associated genes in the Bacillus genus. This manuscript describes methods to prepare and characterize a protein product of the first gene (ba1554) from the gene cluster in B. anthracis using a recombinant protein of its ortholog in B. cereus, bc1531.

Recombinant Protein Expression, Crystallization, and Biophysical Studies of a Bacillus-conserved Nucleotide Pyrophosphorylase, BcMazG

Bacillus anthracis is the obligate pathogen of fatal inhalational anthrax, so studies of its genes and proteins are strictly regulated. An alternative approach is to study orthologous genes. We describe biophysicochemical studies of a B. anthracis ortholog in B. cereus, bc1531, requiring minimal experimental equipment and lacking serious safety concerns.

To overcome safety restrictions and regulations when studying genes and proteins from true pathogens, their homologues can be studied. Bacillus anthracis ...

Characterization of Glycoproteins with the Immunoglobulin Fold by X-Ray Crystallography and Biophysical Techniques

Glycoproteins on the surface of cells play critical roles in cellular function, including signalling, adhesion and transport. On leukocytes, several of these glycoproteins possess immunoglobulin (Ig) folds and are central to immune recognition and regulation. Here, we present a platform for the design, expression and biophysical characterization of the extracellular domain of human B cell receptor CD22. We propose that these approaches are broadly applicable to the characterization of mammalian glycoprotein ectodomains containing Ig domains. Two suspension human embryonic kidney (HEK) cell lines, HEK293F and HEK293S, are used to express glycoproteins harbouring complex and high-mannose glycans, respectively. These recombinant glycoproteins with different glycoforms allow investigating the effect of glycan size and composition on ligand binding. We discuss protocols for studying the kinetics and thermodynamics of glycoprotein binding to biologically relevant ligands and therapeutic antibody candidates. Recombinant glycoproteins produced in HEK293S cells are amenable to crystallization due to glycan homogeneity, reduced flexibility and susceptibility to endoglycosidase H treatment. We present methods for soaking glycoprotein crystals with heavy atoms and small molecules for phase determination and analysis of ligand binding, respectively. The experimental protocols discussed here hold promise for the characterization of mammalian glycoproteins to give insight into their function and investigate the mechanism of action of therapeutics.

We present approaches for the biophysical and structural characterization of glycoproteins with the immunoglobulin fold by biolayer interferometry, isothermal titration calorimetry, and X-ray crystallography.

Glycoproteins on the surface of cells play critical roles in cellular function, including signalling, adhesion and transport. On leukocytes, several of ...

Purification and Reconstitution of TRPV1 for Spectroscopic Analysis

Polymodal ion channels transduce multiple stimuli of different natures into allosteric changes; these dynamic conformations are challenging to determine and remain largely unknown. With recent advances in single-particle cryo-electron microscopy (cryo-EM) shedding light on the structural features of agonist binding sites and the activation mechanism of several ion channels, the stage is set for an in-depth dynamic analysis of their gating mechanisms using spectroscopic approaches. Spectroscopic techniques such as electron paramagnetic resonance (EPR) and double electron-electron resonance (DEER) have been mainly restricted to the study of prokaryotic ion channels that can be purified in large quantities. The requirement for large amounts of functional and stable membrane proteins has hampered the study of mammalian ion channels using these approaches. EPR and DEER offer many advantages, including determination of the structure and dynamic changes of mobile protein regions, albeit at low resolution, that might be difficult to obtain by X-ray crystallography or cryo-EM, and monitoring reversible gating transition (i.e., closed, open, sensitized, and desensitized). Here, we provide protocols for obtaining milligrams of functional detergent-solubilized transient receptor potential cation channel subfamily V member 1 (TRPV1) that can be labeled for EPR and DEER spectroscopy.

This article describes specific methods to obtain biochemical quantities of detergent-solubilized TRPV1 for spectroscopic analysis. The combined protocols provide biochemical and biophysical tools that can be adapted to facilitate structural and functional studies for mammalian ion channels in a membrane-controlled environment.

Polymodal ion channels transduce multiple stimuli of different natures into allosteric changes; these dynamic conformations are challenging to determine ...

Expression and Purification of Mammalian Bestrophin Ion Channels

The human genome encodes four bestrophin paralogs, namely BEST1, BEST2, BEST3, and BEST4. BEST1, encoded by the BEST1 gene, is a Ca2+-activated Cl- channel (CaCC) predominantly expressed in retinal pigment epithelium (RPE). The physiological and pathological significance of BEST1 is highlighted by the fact that over 200 distinct mutations in the BEST1 gene have been genetically linked to a spectrum of at least five retinal degenerative disorders, such as Best vitelliform macular dystrophy (Best disease). Therefore, understanding the biophysics of bestrophin channels at the single-molecule level holds tremendous significance. However, obtaining purified mammalian ion channels is often a challenging task. Here, we report a protocol for the expression of mammalian bestrophin proteins with the BacMam baculovirus gene transfer system and their purification by affinity and size-exclusion chromatography. The purified proteins have the potential to be utilized in subsequent functional and structural analyses, such as electrophysiological recording in lipid bilayers and crystallography. Importantly, this pipeline can be adapted to study the functions and structures of other ion channels.

The purification of ion channels is often challenging, but once achieved, it can potentially allow in vitro investigations of the functions and structures of the channels. Here, we describe the stepwise procedures for the expression and purification of mammalian bestrophin proteins, a family of Ca2+-activated Cl- channels.

The human genome encodes four bestrophin paralogs, namely BEST1, BEST2, BEST3, and BEST4. BEST1, encoded by the BEST1 gene, is a Ca2+-activated Cl- ...

Expression, Solubilization, and Purification of Eukaryotic Borate Transporters

The Solute Carrier 4 (SLC4) family of proteins is called the bicarbonate transporters and includes the archetypal protein Anion Exchanger 1 (AE1, also known as Band 3), the most abundant membrane protein in the red blood cells. The SLC4 family is homologous with borate transporters, which have been characterized in plants and fungi. It remains a significant technical challenge to express and purify membrane transport proteins to homogeneity in quantities suitable for&#160;structural or functional studies. Here we describe detailed procedures for the overexpression of borate transporters in Saccharomyces cerevisiae, isolation of yeast membranes, solubilization of protein by detergent, and purification of borate transporter homologs from S. cerevisiae, Arabidopsis thaliana, and Oryza sativa. We also detail a glutaraldehyde cross-linking experiment to assay multimerization of homomeric transporters. Our generalized procedures can be applied to all three proteins and have been optimized for efficacy. Many of the strategies developed here can be utilized for the study of other challenging membrane proteins.

Here we present a protocol to express, solubilize, and purify several eukaryotic borate transporters with homology to the SLC4 transporter family using yeast. We also describe a chemical cross-linking assay to assess the purified homomeric proteins for multimeric assembly. These protocols can be adapted for other challenging membrane proteins.

The Solute Carrier 4 (SLC4) family of proteins is called the bicarbonate transporters and includes the archetypal protein Anion Exchanger 1 (AE1, also ...

Co-Translational Insertion of Membrane Proteins into Preformed Nanodiscs

Cell-free expression systems allow the tailored design of reaction environments to support the functional folding of even complex proteins such as membrane proteins. The experimental procedures for the co-translational insertion and folding of membrane proteins into preformed and defined membranes supplied as nanodiscs are demonstrated. The protocol is completely detergent-free and can generate milligrams of purified samples within one day. The resulting membrane protein/nanodisc samples can be used for a variety of functional studies and structural applications such as crystallization, nuclear magnetic resonance, or electron microscopy. The preparation of basic key components such as cell-free lysates, nanodiscs with designed membranes, critical stock solutions as well as the assembly of two-compartment cell-free expression reactions is described. Since folding requirements of membrane proteins can be highly diverse, a major focus of this protocol is the modulation of parameters and reaction steps important for sample quality such as critical basic reaction compounds, membrane composition of nanodiscs, redox and chaperone environment, or DNA template design. The whole process is demonstrated with the synthesis of proteorhodopsin and a G-protein coupled receptor.

Co-translational insertion into pre-formed nanodiscs makes it possible to study cell-free synthesized membrane proteins in defined lipid environments without contact with detergents. This protocol describes the preparation of essential system components and the critical parameters for improving expression efficiency and sample quality.