Name: alternative in vitro methods for the determination of viral capsid structural integrity
Uploaded: 2017-11-16T15:00:00
Description: Watch this Scientific Journal Video about Alternative In Vitro Methods for the Determination of Viral Capsid Structural Integrity at JoVE.com

This work was supported by the Agriculture and Food Research Initiative Competitive Grant no. 2011-68003-30395 from the United States Department of Agriculture, National Institute of Food and Agriculture through the NoroCORE project. Funding for open access charge was provided by the United States Department of Agriculture. We would like to thank Robert Atmar (Baylor College of Medicine, Houston, TX) for kindly providing us the purified capsids and Valerie Lapham for her assistance with the TEM images. We would also like to thank Frank N. Barry for helping us start the experiments presented.

1. Plate-based Binding Assay for Evaluating Loss of Higher Order Norovirus Capsid Structure
NOTE: A very similar ELASA protocol to the one presented here has been published29, and similar ELASA assays have previously been reported as part of research articles elsewhere17,18,22.
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	<li>Heat treatment of human norovirus GII.4 Sydney capsids
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		<li>Obtai...

<ol>
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The protocol and techniques described here provide a means of assessing human norovirus capsid integrity/functionality. These methods can be used for obtaining mechanistic insight into the effects of inactivation treatments against the virus, and can potentially supplement more traditional inactivation evaluation methods such as RT-qPCR or plaque assay. For instance, the evaluation of chemical or physical inactivation by plaque assay alone provides a measure of degree of virus inactivation but not the underlying mechanis...

Human norovirus is responsible for a considerable public health burden globally, causing about 685 million illnesses and 212,000 deaths annually1, at a cost in the billions of dollars2,3. Today, norovirus detection and quantification involves genome amplification and/or ligand-based platforms. The former is generally preferred as it is more sensitive, provides quantitative information, and has generally lower risk of false positive results4. The most common norovirus detection and quantification genome amplification technique is reverse transcriptase quantitative polymerase chain reaction (RT-qPCR). Because it targets and amplifies a small segment of the human norovirus genome, RT-qPCR alone is not capable of discriminating between infectious and non-infectious particles, as free genomic RNA, damaged capsids containing genomes, and capsids with fatally mutated/truncated genomes can still be amplified by RT-qPCR. While two new in vitro cultivation techniques for human norovirus5,6 have been reported recently, both still rely on RT-qPCR for virus quantification and are not yet feasible methods for routine clinical/environmental testing for human noroviruses. Thus, RT-qPCR remains the gold standard for clinical/environmental testing.
Other in vitro methods have been developed in an effort to better estimate the infectivity status of norovirus particles. These methods can be generally categorized as those that address the integrity of the norovirus capsid and those evaluating genome integrity. The former approach is more popular. A commonly used method is RNase pretreatment prior to extraction of viral genomic RNA, however this does not account for viral particles that remain intact but lack the ability to bind host receptors/co-factors, as well as viral particles that have fatally mutated or have truncated or marginally damaged genomes7. Capsid integrity can also be evaluated based on the ability of the virus to bind to human norovirus co-receptor/co-factors, which are carbohydrates known as histo-blood group antigens (HBGAs). HBGAs are present in host intestinal epithelial cells as part of glycoproteins or glycolipids (among multiple other tissues) and may be secreted in bodily fluids like saliva. Enteric bacteria containing HBGA-like substances on their surfaces have also been shown to bind human norovirus8,9,10, and such interactions may promote norovirus infection5. The basic concept of utilizing HBGA binding is that only viral particles capable of binding the putative receptor/co-factor would be capable of infecting cells. Multiple studies suggest that bead-based HBGA binding preceding nucleic acid amplification is a promising method for infectivity discrimination11,12,13,14,15,16. A major challenge regarding HBGAs is that no single HBGA type can bind all human norovirus genotypes. To address this, porcine gastric mucin, which contains HBGAs, has been used in place of purified HBGA carbohydrates in the interest of ease of synthesis, consistency, and reduced cost.
A recent publication by Moore et al.17 introduced a set of new techniques for estimating human norovirus capsid integrity. In place of HBGAs, Moore et al.17 investigated binding of a broadly reactive nucleic acid aptamer (M6-2)18 and broadly reactive monoclonal antibody (NS14)19 to heat-treated GII.4 Sydney norovirus capsids (virus-like particles or VLPs) and compared this to the binding to synthetic HBGAs. Nucleic acid aptamers are short (~20 - 80 nt) single stranded nucleic acids (ssDNA or RNA) that fold into unique three-dimensional structures as a consequence of their sequence and bind a target. Because they are nucleic acids, they are less costly; easily chemically synthesized, purified, and modified; and stable to heat. Several reports of aptamers generated against noroviruses exist, with some of them showing broad reactivity to a variety of strains18,20,21,22. By way of example, Moore et al.17 demonstrated that aptamer M6-2 bound to purified, assembled human norovirus capsids (VLPs) and behaved similarly to HBGA in the reliance on the viral capsid to maintain higher order (e.g., secondary and tertiary) protein structure for binding to occur. On the other hand, a significant proportion of norovirus VLP binding to antibody NS14 remained after capsids were completely denatured. Evaluation of norovirus binding in the study by Moore et al.17 was done using a simple, plate-based method similar to ELISA, with the exception that aptamers are used in place of antibodies (hence the method was called ELASA). This high throughput experimental method was used to evaluate the effects of different treatments on the norovirus capsid, work that is valuable for understanding the mechanism of viral inactivation upon exposure to physical or chemical stressors. However, one drawback to this method is the lower sensitivity and lack of tolerance for matrix-associated contaminants at higher levels that cause non-specific binding by aptamers.
Moore et al.17 used another method, dynamic light scattering (DLS), to monitor aggregation of viral particles in response to heat treatment. DLS is commonly used to evaluate the size of nanoparticle suspensions and has been extended to proteins23,24 and viruses25,26,27. The intensity of light scattered by particles in solution fluctuates as a function of particle size, allowing for the calculation of diffusion coefficient and then particle diameter using well-established formulae. The DLS technique can distinguish the hydrodynamic diameter of dispersed particles down to the nanoscale, which allows detection of dispersed viruses, individual capsid proteins or dimers, and virus aggregates based on size27. Virus aggregation, represented by an increase in particle size, is indicative of loss of capsid integrity. As the capsid is denatured and its structure disrupted, hydrophobic residues become exposed and cause the particles to stick together and form aggregates. DLS can be used to measure particle size after a specified treatment or the kinetics of aggregation in real time17,28. This method has the advantage of allowing observation of capsid behavior in solution but requires high concentrations of purified capsid, which may not be entirely representative of the virus in its natural state.
The final method utilized by Moore et al.17 was transmission electron microscopy (TEM). Although this method lacks sensitivity and does not produce quantitative data, it allows for visualization of the effects of different treatments on the viral capsid structure. Although not yet ideal for clinical/environmental settings, the use of these methods in combination is valuable in understanding human norovirus inactivation. The purpose of this article is to provide in-depth protocols for the plate-based binding assay (ELASA), DLS, and TEM preparation methods used to investigate the effects of heat treatments on the norovirus capsid in the context of the treatments&#39; effects on capsid integrity as presented in Moore et al.17.

<table>
	<tbody>
		<tr>
			<td>Plate-Based Binding Assay for Evaluating Loss of Higher Order Norovirus Capsid Structure</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>96-well, medium-binding polystyrene EIA plate</td>
			<td>Fisher (Costar)</td>
			<td>07-200-36</td>
			<td></td>
		</tr>
		<tr>
			<td>Lid for 96-well plate</td>
			<td>Thermo Fisher</td>
			<td>3098</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraffin film (Parafilm)</td>
			<td>Thermo Fisher</td>
			<td>PM999</td>
			<td></td>
		</tr>
		<tr>
			<td>1x PBS (pH 7.2)</td>
			<td>Life Technologies</td>
			<td>20012-050</td>
			<td></td>
		</tr>
		<tr>
			<td>Polysorbate 20</td>
			<td>Sigma-Aldrich</td>
			<td>P9416</td>
			<td></td>
		</tr>
		<tr>
			<td>1x PBS (pH 7.2) + 0.05% Polysorbate 20</td>
			<td>N/A</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Purified, assembled human norovirus GII.4 capsids</td>
			<td>N/A</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Individual 0.2 ml PCR tubes</td>
			<td>Genesee Scientific</td>
			<td>22-154G</td>
			<td></td>
		</tr>
		<tr>
			<td>2 thermocyclers</td>
			<td>Bio-Rad</td>
			<td>1861096</td>
			<td></td>
		</tr>
		<tr>
			<td>Tabletop mini centrifuge</td>
			<td>Fisher Scientific</td>
			<td>12-006-901</td>
			<td></td>
		</tr>
		<tr>
			<td>Skim milk solids</td>
			<td>Thermo Fisher</td>
			<td>LP0031B</td>
			<td></td>
		</tr>
		<tr>
			<td>Synthetic histo-blood group type A disaccharide, biotinylated</td>
			<td>Glycotech</td>
			<td>01-017</td>
			<td></td>
		</tr>
		<tr>
			<td>Biotinylated aptamer M6-2 (stock concentration 100 &#181;M in nuclease-free water): 5&#39;-/5Biosg/AGTATACGTATTACCTGCAGCTGGGAAGAGGTCCGGTAAATGCAGGGTCAGCCCGGAGAGCGATATCTCGGAGATCTTGC -3&#8217;</td>
			<td>Integrated DNA Technologies</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptavidin-horseradish peroxidase conjugate (ELISA grade), We use Life Technologies SNN2004</td>
			<td>Life Technologies</td>
			<td>SNN2004</td>
			<td></td>
		</tr>
		<tr>
			<td>3,3&#8217;,5,5&#8217;-tetramethylbenzidine (TMB) substrate, room temperature</td>
			<td>Thermo Fisher</td>
			<td>50-76-00</td>
			<td></td>
		</tr>
		<tr>
			<td>1 M phosphoric acid</td>
			<td>N/A</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Microplate reader capable of reading 450 nm</td>
			<td>Tecan</td>
			<td>Infinite m200 Pro</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Analysis of Plate-Based Assay Results</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Microsoft Excel or similar program</td>
			<td>N/A</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Dynamic Light Scattering Experiments</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Zetasizer ZSP, or similar particle size analysis instrument</td>
			<td>Malvern Instruments</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Vortex</td>
			<td>Fisher Scientifc</td>
			<td>02-215-365</td>
			<td></td>
		</tr>
		<tr>
			<td>Quartz cuvette</td>
			<td>Hellma</td>
			<td>104-002-10-40</td>
			<td></td>
		</tr>
		<tr>
			<td>Small volume disposable cuvette (to reduce VLP use)</td>
			<td>Malvern Instruments</td>
			<td>ZEN0040</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Transmission Electron Microscopy Sample Preparation</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Nickel electron microscopy grids with carbon support film</td>
			<td>Ladd Research</td>
			<td>10880-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Self-closing reverse electron microscopy tweezers</td>
			<td>Ted Pella</td>
			<td>5372-NM</td>
			<td></td>
		</tr>
		<tr>
			<td>Qualitative filter paper</td>
			<td>Sigma-Aldrich (Whatman)</td>
			<td>WHA1002055</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass petri dishes</td>
			<td>Sigma-Aldrich</td>
			<td>BR455743</td>
			<td></td>
		</tr>
		<tr>
			<td>100 mM stock HEPES solution (pH 7.2)</td>
			<td>N/A</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>2% uranyl acetate</td>
			<td>N/A</td>
			<td>N/A</td>
			<td></td>
		</tr>
	</tbody>
</table>

alternative in vitro methods for the determination of viral capsid structural integrity

Human norovirus exacts considerable public health and economic losses worldwide. Emerging in vitro cultivation advances are not yet applicable for routine detection of the virus. The current detection and quantification techniques, which rely primarily on nucleic acid amplification, do not discriminate infectious from non-infectious viral particles. The purpose of this article is to present specific details on recent advances in techniques used together in order to acquire further information on the infectivity status of viral particles. One technique involves assessing binding of a norovirus ssDNA aptamer to capsids. Aptamers have the advantage of being easily synthesized and modified, and are inexpensive and stable. Another technique, dynamic light scattering (DLS), has the advantage of observing capsid behavior in solution. Electron microscopy allows for visualization of the structural integrity of the viral capsids. Although promising, there are some drawbacks to each technique, such as non-specific aptamer binding to positively-charged molecules from sample matrices, requirement of purified capsid for DLS, and poor sensitivity for electron microscopy. Nonetheless, when these techniques are used in combination, the body of data produced provides more comprehensive information on norovirus capsid integrity that can be used to infer infectivity, information which is essential for accurate evaluation of inactivation methods or interpretation of virus detection. This article provides protocols for using these methods to discriminate infectious human norovirus particles.

The structural integrity of human norovirus GII.4 Sydney capsids (VLPs) was assessed using several novel methods as presented by Moore et al.17. First, an experiment was done in which the integrity of the capsids as a function of their ability to bind a putative receptor/co-factor (HBGA) or ssDNA aptamer (M6-2) were compared (Figure 1). The results displayed have been previously presented by Moore et al.<sup class="xr...

Watch this Scientific Journal Video about Alternative In Vitro Methods for the Determination of Viral Capsid Structural Integrity at JoVE.com

Alternative In Vitro Methods for the Determination of Viral Capsid Structural Integrity

Routine detection methods utilizing viral genome amplification are limited by their inability to discriminate infectious from non-infectious particles. The purpose of this article is to provide detailed protocols for alternative methods to aid in discrimination of infectious norovirus particles using aptamer binding, dynamic light scattering, and transmission electron microscopy.

Alternative In Vitro Methods for the Determination of Viral Capsid Structural Integrity

Human norovirus exacts considerable public health and economic losses worldwide. Emerging in vitro cultivation advances are not yet applicable for routine ...

The overall goal of these methods is to gain further insight into the effects of a treatment on the infectivity or integrity of the human norovirus capsid. This method can help answer key questions in the field of non-enveloped viral inactivation. Such as what is happening to the viral capsid's ability to infect a cell after a given treatment.The main advantage of these methods is that they can provide additional mechanistic insight into the action of any given treatment on the virus. Though this method can provide the insight into human norovirus inactivation strategies, it also has potential to be applied to other non-enveloped viruses such as rhinovirus or hepatitis A.To begin, dilute purified human norovirus major capsid protein, assembled in capsids to 50 micrograms per milliliter in 1X phosphate buffered saline. Use a maximum volume of 15 microliters in the individual capped PCR tubes.Ensure that the tube contains at least 600 nanograms of capsid and that there is 600 nanograms of capsid per treatment ligand combination. Next, preheat the thermocycler to the desired heat treatment. Then, preheat an additional thermocycler to four degrees celsius for immediate cooling.Add the tubes with capsid solution to the thermocycler for the desired time. After heating, immediately transfer the tubes to the precooled four degrees celsius cycler for five minutes. Briefly spin down the tubes in the centrifuge to get all the droplets to the bottom of the tube.Dilute the treated capsid solutions and PBS to three micrograms per milliliter. Ensure that there is at least 200 microliters of diluted treated capsid. Next, apply 100 microliters of capsid solution to each well ensure that there are at least two wells per treatment.Additionally, include two control wells with 100 microliters of PBS for each ligand. This provides the background absorbance of the assay. Cover the plate with a lid and seal the edges with paraffin film to reduce evaporation.Leave the plate overnight on a shaking incubator at four degrees celsius or for two hours at room temperature. Following incubation, remove the treated capsid solutions from the plate. Then, add 200 microliters per well of blocking buffer.Incubate for two hours at room temperature or sealed at four degrees celsius overnight. Meanwhile, dilute the biotinylated aptamer to one micromolar in nuclease-free water. Ensure that there is enough solution for 200 microliters total for each treatment.Also, dilute the chosen biotinylated HPGA to 30 microliters per milliliter in the blocking buffer. Again, ensure that there is enough solution for 200 microliters total volume for each treatment. Following incubation, remove the blocking buffer and wash the plate three times with 200 microliters per well of PBST.Pat the plate upside down on sterile paper towels to dry the residual moisture. Next, at 100 microliters per well of the ligand binding solutions ensuring that there are two wells per heat treatment ligand combination, incubate the covered plate on an orbital shaker at about 60 RPM for one hour at room temperature. After washing the wells as described in the text protocol add 100 microliters per well of 0.2 micrograms per milliliter of streptavidin horseradish peroxidase and PBS.Incubate for 15 minutes at room temperature with gentle shaking on an orbital shaker before washing the wells again. Then, after another wash, add 100 microliters per well of TMB substrate and allow the color to develop for five to 15 minutes. Observe the wells for color.Be sure to consistently develop for the same time between replicate plates and be aware of the absorbance range of the plate reader used. Stop the development of the reaction with 100 microliters per well of one molar phosphoric acid. Immediately read the plate at 450 nanometers.Create a new size standard operating procedure in the DLS instrument software as detailed in the text protocol. Then, select the green run arrow within the software and name the sample. Dilute the heat-treated virus-like particles or VLPs one to 10 in 1X PBS for final concentration of five micrograms per milliliter.Then, filter the sample with a one micron pore size to remove dust particles. DLS is very sensitive to dust, as large particles scattered much more light than small particles. Transfer 50 microliters of the diluted VLPs into a small volume disposable cuvette.Insert the cuvette into the sample chamber of the instrument. Start the run and use the correlogram cumulant fit and expert advice tabs to evaluate the data quality. During the run, check that the poly disperse of the index value is less than 0.3 representing a quality measurement.In the multiview tab, make sure the correlation coefficient is constant and close to but not more than one at a short time and drops off sharply at zero at a later time, characteristic of particle size. Use the expert advice tab for feedback on the data quality during the measurements. After the measurement is complete, check again at the poly disperse of the index value is less than 0.3.Make sure that the cumulant fit line follows the data points closely in the cumulants fit tab. Create a new size standard operating procedure in the DLS instrument software as detailed in the text protocol. Select the run arrow within the software to open and name a new sample and allow the instrument to reach the temperature equilibrium.Transfer the VLP suspension to a small volume quartz cuvette avoid bubbles and pipette slowly against the wall of the cuvette. After the instrument has reached temperature equilibrium, insert the cuvette into the sample chamber. After waiting 10 seconds for the sample temperature to equilibrate, start the run and simultaneously start a timer.Stop the timer at the end of the first measurement. Take this time as the first time point. Obtain subsequent time points from the measurement times recorded by the software.Perform heat treatment as before except substitute PBS for 10 millimolar heaps, pH 7.4 and do not further dilute capsids after treatment. Next, pipette the entire 15 microliter drop of treated capsid solution onto paraffin film. Grab the grid edge with tweezers allowing them to close on the edge to hold the grid and place grid carbon side down on top of the drop of treated solution.Let the grid incubated for 10 minutes to allow the capsid to attach to the grid. Depending on the purity of the capsid preparation, add washes of the heap solution in the form of 10 to 15 microliter droplets placed in line after the treated capsid droplet. After 10 minutes, pick up the grid with the droplet.Place the grid nearly perpendicular to a piece of filter paper to wick away the droplet. Then, use the grid to pick up the droplet of 10 to 15 microliter heaps buffer and hold it for 30 seconds. After 30 seconds of wash time wick away with another piece of filter paper.Next, place a 15 microliter droplet of two percent uranyl acetate solution on the paraffin film in an empty area. Pick up the droplet of uranyl acetate with the grid and hold it for 45 seconds. Then, wick away the uranyl acetate being sure to remove most of the solution.Place the grid carbon side up on a piece of filter paper being careful that the grid does not stick to the moisture on the tweezers. Then, place the filter paper with the grid on it in an open glass petri dish. After repeating this process for all treatments, place the petri dish halves with the grids in a desiccator overnight to dry prior to observing with TEM.The following graph displays reduction of the binding ability of human norovirus capsids over time when treated at 68 degrees celsius. As can be seen, HPGA binding is the first signal to completely disappear. At this point, it is assumed that the large majority of capsids in the solution have lost the ability to bind host cell HPGAs and thus cannot be internalized into the cell.Aptamer binding mirrors that of HBGA, though slightly more heat treatment is required to remove the signal. Shown here is a DLS correlation coefficient curve representative of good quality data. At time close to zero, the correlogram is constant at a value close to, but below one.It then drops off sharply to zero at a time characteristic of the particle size. Size results from this experiment can likely be trusted. Conversely, this correlation coefficient curve is representative of poor quality data.The correlogram starts at a value above one and gradually drops off to zero. Results from this experiment should not be used. Here, particle size data shows a clear aggregation profile for capsids treated at 68 degrees celsius with super aggregates forming after about 20 minutes.The time at which the super aggregation occurs is characteristic of the susceptibility of the VLPs to that treatment. This figure visualizes the TEM results for heat treatment of human norovirus capsids. Here, the capsids were being treated at 60 to 80 degrees celsius from left to right.As can be seen, capsid morphology clearly changes with treatment as capsids aggregate and denature. A similar phenomenon is noted for capsids treated at 68 degrees celsius for zero to 25 minutes. Once mastered, these techniques can be done in one to 24 hours if they are performed properly.After its development, this technique provided an additional avenue for researchers in the field of food virology to explore the mechanisms and effects of inactivation on the capsid of human noroviruses. Following this procedure, other methods like a real-time RT-PCR with and without RNase pretreatment, STS page of viral capsids, and plaque assays with cultivable surrogate viruses can be performed to get a more complete overall view of viral reduction after a given treatment. After watching this video, you should have a good understanding of how to utilize ligand binding, dynamic light scattering, and transmission electron microscopy to gain further mechanistic insights into the effects of inactivation treatment on the human norovirus capsid.Don't forget that working with some of the reagents used can be hazardous and precautions such as wearing personal protective equipment and following laboratory safety best practices should always be taken while performing this procedure.

alternative-vitro-methods-for-determination-viral-capsid-structural

Research

JoVE Journal

Immunology and Infection

Structure of HIV-1 Capsid Assemblies by Cryo-electron Microscopy and Iterative Helical Real-space Reconstruction

Cryo-electron microscopy (cryo-EM), combined with image processing, is an increasingly powerful tool for structure determination of macromolecular protein complexes and assemblies. In fact, single particle electron microscopy1 and two-dimensional (2D) electron crystallography2 have become relatively routine methodologies and a large number of structures have been solved using these methods. At the same time, image processing and three-dimensional (3D) reconstruction of helical objects has rapidly developed, especially, the iterative helical real-space reconstruction (IHRSR) method3, which uses single particle analysis tools in conjunction with helical symmetry. Many biological entities function in filamentous or helical forms, including actin filaments4, microtubules5, amyloid fibers6, tobacco mosaic viruses7, and bacteria flagella8, and, because a 3D density map of a helical entity can be attained from a single projection image, compared to the many images required for 3D reconstruction of a non-helical object, with the IHRSR method, structural analysis of such flexible and disordered helical assemblies is now attainable.
In this video article, we provide detailed protocols for obtaining a 3D density map of a helical protein assembly (HIV-1 capsid9 is our example), including protocols for cryo-EM specimen preparation, low dose data collection by cryo-EM, indexing of helical diffraction patterns, and image processing and 3D reconstruction using IHRSR. Compared to other techniques, cryo-EM offers optimal specimen preservation under near native conditions. Samples are embedded in a thin layer of vitreous ice, by rapid freezing, and imaged in electron microscopes at liquid nitrogen temperature, under low dose conditions to minimize the radiation damage. Sample images are obtained under near native conditions at the expense of low signal and low contrast in the recorded micrographs. Fortunately, the process of helical reconstruction has largely been automated, with the exception of indexing the helical diffraction pattern. Here, we describe an approach to index helical structure and determine helical symmetries (helical parameters) from digitized micrographs, an essential step for 3D helical reconstruction. Briefly, we obtain an initial 3D density map by applying the IHRSR method. This initial map is then iteratively refined by introducing constraints for the alignment parameters of each segment, thus controlling their degrees of freedom. Further improvement is achieved by correcting for the contrast transfer function (CTF) of the electron microscope (amplitude and phase correction) and by optimizing the helical symmetry of the assembly.

This article describes a method to obtain a three-dimensional (3D) structure of helically assembled molecules using cryo-electron microscopy. In this protocol, we use HIV-1 capsid assemblies to illustrate the detailed 3D reconstruction procedure for achieving a density map by the iterative helical real-space reconstruction method.

Cryo-electron microscopy (cryo-EM), combined with image processing, is an increasingly powerful tool for structure determination of macromolecular protein ...

Establishing a Liquid-covered Culture of Polarized Human Airway Epithelial Calu-3 Cells to Study Host Cell Response to Respiratory Pathogens In vitro

The apical and basolateral surfaces of airway epithelial cells demonstrate directional responses to pathogen exposure in vivo. Thus, ideal in vitro models for examining cellular responses to respiratory pathogens polarize, forming apical and basolateral surfaces. One such model is differentiated normal human bronchial epithelial cells (NHBE). However, this system requires lung tissue samples, expertise isolating and culturing epithelial cells from tissue, and time to generate an air-liquid interface culture.
Calu-3 cells, derived from a human bronchial adenocarcinoma, are an alternative model for examining the response of proximal airway epithelial cells to respiratory insult1, pharmacological compounds2-6, and bacterial7-9 and viral pathogens, including influenza virus, rhinovirus and severe acute respiratory syndrome - associated coronavirus10-14. Recently, we demonstrated that Calu-3 cells are susceptible to respiratory syncytial virus (RSV) infection in a manner consistent with NHBE15,16 . Here, we detail the establishment of a polarized, liquid-covered culture (LCC) of Calu-3 cells, focusing on the technical details of growing and culturing Calu-3 cells, maintaining cells that have been cultured into LCC, and we present the method for performing respiratory virus infection of polarized Calu-3 cells.
To consistently obtain polarized Calu-3 LCC, Calu-3 cells must be carefully subcultured before culturing in Transwell inserts. Calu-3 monolayer cultures should remain below 90% confluence, should be subcultured fewer than 10 times from frozen stock, and should regularly be supplied with fresh medium. Once cultured in Transwells, Calu-3 LCC must be handled with care. Irregular media changes and mechanical or physical disruption of the cell layers or plates negatively impact polarization for several hours or days. Polarization is monitored by evaluating trans-epithelial electrical resistance (TEER) and is verified by evaluating the passive equilibration of sodium fluorescein between the apical and basolateral compartments17,18 . Once TEER plateaus at or above 1,000 &Omega;&times;cm2, Calu-3 LCC are ready to use to examine cellular responses to respiratory pathogens.

Establishing a Liquid-covered Culture of Polarized Human Airway Epithelial Calu-3 Cells to Study Host Cell Response to Respiratory Pathogens In vitro

The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.

The  apical and basolateral surfaces of airway epithelial cells demonstrate  directional responses to pathogen exposure in  vivo. Thus, ideal in vitro ...

Averaging of Viral Envelope Glycoprotein Spikes from Electron Cryotomography Reconstructions using Jsubtomo

Enveloped viruses utilize membrane glycoproteins on their surface to mediate entry into host cells. Three-dimensional structural analysis of these glycoprotein &#8216;spikes&#8217; is often technically challenging but important for understanding viral pathogenesis and in drug design. Here, a protocol is presented for viral spike structure determination through computational averaging of electron cryo-tomography data. Electron cryo-tomography is a technique in electron microscopy used to derive three-dimensional tomographic volume reconstructions, or tomograms, of pleomorphic biological specimens such as membrane viruses in a near-native, frozen-hydrated state. These tomograms reveal structures of interest in three dimensions, albeit at low resolution. Computational averaging of sub-volumes, or sub-tomograms, is necessary to obtain higher resolution detail of repeating structural motifs, such as viral glycoprotein spikes. A detailed computational approach for aligning and averaging sub-tomograms using the Jsubtomo software package is outlined. This approach enables visualization of the structure of viral glycoprotein spikes to a resolution in the range of 20-40 &#197; and study of the study of higher order spike-to-spike interactions on the virion membrane. Typical results are presented for Bunyamwera virus, an enveloped virus from the family Bunyaviridae. This family is a structurally diverse group of pathogens posing a threat to human and animal health.

An approach is presented for determining structures of viral membrane glycoprotein complexes using a combination of electron cryo-tomography and sub-tomogram averaging with the computational package Jsubtomo.

Enveloped viruses utilize membrane glycoproteins on their surface to mediate entry into host cells. Three-dimensional structural analysis of these ...

Viral Concentration Determination Through Plaque Assays: Using Traditional and Novel Overlay Systems

Plaque assays remain one of the most accurate methods for the direct quantification of infectious virons and antiviral substances through the counting of discrete plaques (infectious units and cellular dead zones) in cell culture. Here we demonstrate how to perform a basic plaque assay, and how differing overlays and techniques can affect plaque formation and production. Typically solid or semisolid overlay substrates, such as agarose or carboxymethyl cellulose, have been used to restrict viral spread, preventing indiscriminate infection through the liquid growth medium. Immobilized overlays restrict cellular infection to the immediately surrounding monolayer, allowing the formation of discrete countable foci and subsequent plaque formation. To overcome the difficulties inherent in using traditional overlays, a novel liquid overlay utilizing microcrystalline cellulose and carboxymethyl cellulose sodium has been increasingly used as a replacement in the standard plaque assay. Liquid overlay plaque assays can be readily performed in either standard 6 or 12 well plate formats as per traditional techniques and require no special equipment. Due to its liquid state and subsequent ease of application and removal, microculture plate formats may alternatively be utilized as a rapid, accurate and high throughput alternative to larger scale viral titrations. Use of a non heated viscous liquid polymer offers the opportunity to streamline work, conserves reagents, incubator space, and increases operational safety when used in traditional or high containment labs as no reagent heating or glassware are required. Liquid overlays may also prove more sensitive than traditional&#160;overlays for certain heat labile viruses.

Plaque assays are the gold standard for viral quantification, utilizing entrapping overlays on host cellular monolayers to determine viral titers. While various semisolid overlays have traditionally been used, here we demonstrate plaque techniques comparing semisolid overlays to a novel liquid microcrystalline cellulose among several families of viruses.

Plaque assays remain one of the most accurate methods for the direct quantification of infectious virons and antiviral substances through the counting of ...

Detecting Glycogen in Peripheral Blood Mononuclear Cells with Periodic Acid Schiff Staining

Periodic acid Schiff (PAS) staining is an immunohistochemical technique used on muscle biopsies and as a diagnostic tool for blood samples. Polysaccharides such as glycogen, glycoproteins, and glycolipids stain bright magenta making it easy to enumerate positive and negative cells within the tissue. In muscle cells PAS staining is used to determine the glycogen content in different types of muscle cells, while in blood cell samples PAS staining has been explored as a diagnostic tool for a variety of conditions. Blood contains a proportion of white blood cells that belong to the immune system. The notion that cells of the immune system possess glycogen and use it as an energy source has not been widely explored. Here, we describe an adapted version of the PAS staining protocol that can be applied on peripheral blood mononuclear immune cells from human venous blood. Small cells with PAS-positive granules and larger cells with diffuse PAS staining were observed. Treatment of samples with amylase abrogates these patterns confirming the specificity of the stain. An alternate technique based on enzymatic digestion confirmed the presence and amount of glycogen in the samples. This protocol is useful for hematologists or immunologists studying polysaccharide content in blood-derived lymphocytes.

Periodic acid Schiff staining is a technique that visualizes the polysaccharide content of tissues. This article demonstrates periodic acid Schiff staining protocol adapted for use on peripheral blood mononuclear cells purified from human venous blood. Such samples are enriched for lymphocytes and other white blood cells of the immune system.

Periodic acid Schiff (PAS) staining is an immunohistochemical technique used on muscle biopsies and as a diagnostic tool for blood samples. ...

Utilizing the Antigen Capsid-Incorporation Strategy for the Development of Adenovirus Serotype 5-Vectored Vaccine Approaches

Adenovirus serotype 5 (Ad5) has been extensively modified with traditional transgene methods for the vaccine development. The reduced efficacies of these traditionally modified Ad5 vectors in clinical trials could be primarily correlated with Ad5 pre-existing immunity (PEI) among the majority of the population. To promote Ad5-vectored vaccine development by solving the concern of Ad5 PEI, the innovative Antigen Capsid-Incorporation strategy has been employed. By merit of this strategy, Ad5-vectored we first constructed the hexon shuttle plasmid HVR1-KWAS-HVR5-His6/pH5S by subcloning the hypervariable region (HVR) 1 of hexon into a previously constructed shuttle plasmid HVR5-His6/pH5S, which had His6 tag incorporated into the HVR5. This HVR1 DNA fragment containing a HIV epitope ELDKWAS was synthesized. HVR1-KWAS-HVR5-His6/pH5S was then linearized and co-transformed with linearized backbone plasmid pAd5/&#8710;H5 (GL) , for homologous recombination. This recombined plasmid pAd5/H5-HVR1-KWAS-HVR5-His6 was transfected into cells to generate the viral vector Ad5/H5-HVR1-KWAS-HVR5-His6. This vector was validated to have qualitative fitness indicated by viral physical titer (VP/ml), infectious titer (IP/ml) and corresponding VP/IP ratio. Both the HIV epitope and His6 tag were surface-exposed on the Ad5 capsid, and retained epitope-specific antigenicity of their own. A neutralization assay indicated the ability of this divalent vector to circumvent neutralization by Ad5-positive sera in vitro. Mice immunization demonstrated the generation of robust humoral immunity specific to the HIV epitope and His6. This proof-of-principle study suggested that the protocol associated with the Antigen Capsid-Incorporation strategy could be feasibly utilized for the generation of Ad5-vectored vaccines by modifying different capsid proteins. This protocol could even be further modified for the generation of rare-serotype adenovirus-vectored vaccines.

Here, we present a protocol to generate a proof-of-principle divalent adenovirus type 5 (Ad5) vector Ad5/H5-HVR1-KWAS-HVR5-His6 by utilizing the Antigen Capsid-Incorporation strategy. This vector was demonstrated to exhibit qualitative fitness, the capability to escape Ad5-positive sera in vitro, and the antigenicity as well as immunogenicity to the incorporated antigens.

Adenovirus serotype 5 (Ad5) has been extensively modified with traditional transgene methods for the vaccine development. The reduced efficacies of these ...

The Development of Lyophilized Loop-mediated Isothermal Amplification Reagents for the Detection of Coxiella burnetii

Coxiella burnetii, the agent causing Q fever, is an obligate intracellular bacterium. PCR based diagnostic assays have been developed for detecting C. burnetii DNA in cell cultures and clinical samples. PCR requires specialized equipment and extensive end user training, and therefore, it is not suitable for routine work especially in a resource-constrained area. We have developed a loop-mediated isothermal amplification (LAMP) assay to detect the presence of C. burnetii in patient samples. This method is performed at a single temperature around 60 &#176;C in a water bath or heating block. The sensitivity of this LAMP assay is very similar to PCR with a detection limit of about 25 copies per reaction. This report describes the preparation of the reaction using lyophilized reagents and visualization of results using hydroxynaphthol blue (HNB) or a UV lamp with fluorescent intercalating dye in the reaction. The LAMP reagents were lyophilized and stored at room temperature (RT) for one month without loss of detection sensitivity. This LAMP assay is particularly robust because the reaction mixture preparation does not involve complex steps. This method is ideal for use in resource-limited settings where Q fever is endemic.

The Development of Lyophilized Loop-mediated Isothermal Amplification Reagents for the Detection of Coxiella burnetii

We described here a simple loop-mediated isothermal amplification (LAMP) method using lyophilized reagents for the detection of C. burnetii in patient samples.

Coxiella burnetii, the agent causing Q fever, is an obligate intracellular bacterium. PCR based diagnostic assays have been developed for detecting C. ...

Swab Sampling Method for the Detection of Human Norovirus on Surfaces

Human noroviruses are a leading cause of epidemic and sporadic gastroenteritis worldwide. Because most infections are either spread directly via the person-to-person route or indirectly through environmental surfaces or food, contaminated fomites and inanimate surfaces are important vehicles for the spread of the virus during norovirus outbreaks.
We developed and evaluated a protocol using macrofoam swabs for the detection and typing of human noroviruses from hard surfaces. Compared with fiber-tipped swabs or antistatic wipes, macrofoam swabs allow virus recovery (range 1.2-33.6%) from toilet seat surfaces of up to 700 cm2. The protocol includes steps for the extraction of the virus from the swabs and further concentration of the viral RNA using spin columns. In total, 127 (58.5%) of 217 swab samples that had been collected from surfaces in cruise ships and long-term care facilities where norovirus gastroenteritis had been reported tested positive for GII norovirus by RT-qPCR. Of these 29 (22.8%) could be successfully genotyped. In conclusion, detection of norovirus on environmental surfaces using the protocol we developed may assist in determining the level of environmental contamination during outbreaks as well as detection of virus when clinical samples are not available; it may also facilitate monitoring of effectiveness of remediation strategies.

A macrofoam based sampling methodology was developed and evaluated for the detection and quantification of norovirus on environmental hard surfaces.

Human noroviruses are a leading cause of epidemic and sporadic gastroenteritis worldwide. Because most infections are either spread directly via the ...

In Vitro Methods for Comparing Target Binding and CDC Induction Between Therapeutic Antibodies: Applications in Biosimilarity Analysis

Therapeutic monoclonal antibodies (mAbs) are relevant to the treatment of different pathologies, including cancers. The development of biosimilar mAbs by pharmaceutical companies is a market opportunity, but it is also a strategy to increase drug accessibility and reduce therapy-associated costs. The protocols detailed here describe the evaluation of target binding and CDC induction by rituximab in Daudi cells. These two functions require different structural regions of the antibody and are relevant to the clinical effect induced by rituximab. The protocols allow the side-to-side comparison of a reference rituximab and a marketed rituximab biosimilar. The evaluated products showed differences both in target binding and CDC induction, suggesting that there are underlying physicochemical differences and highlighting the need to analyze the impact of those differences in the clinical setting. The methods reported here constitute simple and inexpensive in vitro models for the evaluation of the activity of rituximab biosimilars. Thus, they can be useful during biosimilar development, as well as for quality control in biosimilar production. Furthermore, the presented methods can be extrapolated to other therapeutic mAbs.

In Vitro Methods for Comparing Target Binding and CDC Induction Between Therapeutic Antibodies: Applications in Biosimilarity Analysis

This protocol describes the in vitro comparison of two key functional characteristics of rituximab: target binding and complement-dependent cytotoxicity (CDC) induction. The methods were employed for a side-to-side comparison between reference rituximab and a rituximab biosimilar. These assays can be employed during biosimilar development or as a quality control in their production.

Therapeutic monoclonal antibodies (mAbs) are relevant to the treatment of different pathologies, including cancers. The development of biosimilar mAbs by ...

Purification of Viral DNA for the Identification of Associated Viral and Cellular Proteins

The goal of this protocol is to isolate herpes simplex virus type 1 (HSV-1) DNA from infected cells for the identification of associated viral and cellular proteins by mass spectrometry. Although proteins that interact with viral genomes play major roles in determining the outcome of infection, a comprehensive analysis of viral genome associated proteins was not previously feasible. Here we demonstrate a method that enables the direct purification of HSV-1 genomes from infected cells. Replicating viral DNA is selectively labeled with modified nucleotides that contain an alkyne functional group. Labeled DNA is then specifically and irreversibly tagged via the covalent attachment of biotin azide via a copper(I)-catalyzed azide-alkyne cycloaddition or click reaction. Biotin-tagged DNA is purified on streptavidin-coated beads and associated proteins are eluted and identified by mass spectrometry. This method enables the selective targeting and isolation of HSV-1 replication forks or whole genomes from complex biological environments. Furthermore, adaptation of this approach will allow for the investigation of various aspects of herpesviral infection, as well as the examination of the genomes of other DNA viruses.

The goal of this protocol is to specifically tag and selectively isolate viral DNA from infected cells for the characterization of viral genome associated proteins.