Binding of fluorescent dye to genomic RNA inside intact human rhinovirus after viral capsid penetration investigated by capillary electrophoresis

Plate-Based High-Throughput Fluorescence Assay for Assessing Enveloped Virus Integrity

Viruses are a considerable threat to global health and place major burdens on economies worldwide. Manufactured viruses are also being widely used as delivery agents to treat (gene therapies) or prevent diseases (vaccines). Therefore, it is vital to study and fully understand the infectious state of viruses. Current techniques used to study viruses are often slow or nonexistent, making the development of new techniques of paramount importance. Here we present a high-throughput and robust, cell-free plate-based assay (FAIRY: Fluorescence Assay for vIRal IntegritY), capable of differentiating intact from nonintact enveloped viruses, i.e, infectious from noninfectious. Using a thiazole orange-terminated polymer, a 99% increase in fluorescence was observed between treated (heat or virucide) and nontreated. The FAIRY assay allowed for the rapid determination of the infectivity of a range of enveloped viruses, highlighting its potential as a valuable tool for the study of viruses and interventions against them.

Sixteen capillary electrophoresis applications for viral vaccine analysis

A broad range of CE applications from our organization is reviewed to give a flavor of the use of CE within the field of vaccine analyses. Applicability of CE for viral vaccine characterization, and release and stability testing of seasonal influenza virosomal vaccines, universal subunit influenza vaccines, Sabin inactivated polio vaccines (sIPV), and adenovirus vector vaccines were demonstrated. Diverse CZE, CE-SDS, CGE, and cIEF methods were developed, validated, and applied for virus, protein, posttranslational modifications, DNA, and excipient concentration determinations, as well as for the integrity and composition verifications, and identity testing (e.g., CZE for intact virus particles, CE-SDS application for hemagglutinin quantification and influenza strain identification, chloride or bromide determination in process samples). Results were supported by other methods such as RP-HPLC, dynamic light scattering (DLS), and zeta potential measurements. Overall, 16 CE methods are presented that were developed and applied, comprising six adenovirus methods, five viral protein methods, and methods for antibodies determination of glycans, host cell-DNA, excipient chloride, and process impurity bromide. These methods were applied to support in-process control, release, stability, process- and product characterization and development, and critical reagent testing. Thirteen methods were validated. Intact virus particles were analyzed at concentrations as low as 0.8 pmol/L. Overall, CE took viral vaccine testing beyond what was previously possible, improved process and product understanding, and, in total, safety, efficacy, and quality.

Rhinovirus Inhibitors: Including a New Target, the Viral RNA

Rhinoviruses (RVs) are the main cause of recurrent infections with rather mild symptoms characteristic of the common cold. Nevertheless, RVs give rise to enormous numbers of absences from work and school and may become life-threatening in particular settings. Vaccination is jeopardised by the large number of serotypes eliciting only poorly cross-neutralising antibodies. Conversely, antivirals developed over the years failed FDA approval because of a low efficacy and/or side effects. RV species A, B, and C are now included in the fifteen species of the genus Enteroviruses based upon the high similarity of their genome sequences. As a result of their comparably low pathogenicity, RVs have become a handy model for other, more dangerous members of this genus, e.g., poliovirus and enterovirus 71. We provide a short overview of viral proteins that are considered potential drug targets and their corresponding drug candidates. We briefly mention more recently identified cellular enzymes whose inhibition impacts on RVs and comment novel approaches to interfere with infection via aggregation, virus trapping, or preventing viral access to the cell receptor. Finally, we devote a large part of this article to adding the viral RNA genome to the list of potential drug targets by dwelling on its structure, folding, and the still debated way of its exit from the capsid. Finally, we discuss the recent finding that G-quadruplex stabilising compounds impact on RNA egress possibly via obfuscating the unravelling of stable secondary structural elements.

Multiple-Monitor HPLC Assays for Rapid Process Development, In-Process Monitoring, and Validation of AAV Production and Purification

HPLC is established as a fast convenient analytical technology for characterizing the content of empty and full capsids in purified samples containing adeno-associated virus (AAV). UV-based monitoring unfortunately over-estimates the proportion of full capsids and offers little value for characterizing unpurified samples. The present study combines dual-wavelength UV monitoring with intrinsic fluorescence, extrinsic fluorescence, and light-scattering to extend the utility of HPLC for supporting development of therapeutic AAV-based drugs. Applications with anion exchange (AEC), cation exchange (CEC), and size exclusion chromatography (SEC) are presented. Intrinsic fluorescence increases sensitivity of AAV detection over UV and enables more objective estimation of empty and full capsid ratios by comparison of their respective peak areas. Light scattering enables identification of AAV capsids in complex samples, plus semiquantitative estimation of empty and full capsid ratios from relative peak areas of empty and full capsids. Extrinsic Picogreen fluorescence enables semiquantitative tracking of DNA with all HPLC methods at all stages of purification. It does not detect encapsidated DNA but reveals DNA associated principally with the exteriors of empty capsids. It also enables monitoring of host DNA contamination across chromatograms. These enhancements support many opportunities to improve characterization of raw materials and process intermediates, to accelerate process development, provide rapid in-process monitoring, and support process validation.

Catching Common Cold Virus with a Net: Pyridostatin Forms Filaments in Tris Buffer That Trap Viruses-A Novel Antiviral Strategy?

The neutrophil extracellular trap (ET) is a eukaryotic host defense machinery that operates by capturing and concentrating pathogens in a filamentous network manufactured by neutrophils and made of DNA, histones, and many other components. Respiratory virus-induced ETs are involved in tissue damage and impairment of the alveolar-capillary barrier, but they also aid in fending off infection. We found that the small organic compound pyridostatin (PDS) forms somewhat similar fibrillary structures in Tris buffer in a concentration-dependent manner. Common cold viruses promote this process and become entrapped in the network, decreasing their infectivity by about 70% in tissue culture. We propose studying this novel mechanism of virus inhibition for its utility in preventing viral infection.

nanoDSF: In vitro Label-Free Method to Monitor Picornavirus Uncoating and Test Compounds Affecting Particle Stability

Thermal shift assays measure the stability of macromolecules and macromolecular assemblies as a function of temperature. The Particle Stability Thermal Release Assay (PaSTRy) of picornaviruses is based on probes becoming strongly fluorescent upon binding to hydrophobic patches of the protein capsid (e.g., SYPRO Orange) or to the viral RNA genome (e.g., SYTO-82) that become exposed upon heating virus particles. PaSTRy has been exploited for studying the stability of viral mutants, viral uncoating, and the effect of capsid-stabilizing compounds. While the results were usually robust, the thermal shift assay with SYPRO Orange is sensitive to surfactants and EDTA and failed at least to correctly report the effect of excipients on an inactivated poliovirus 3 vaccine. Furthermore, interactions between the probe and capsid-binding antivirals as well as mutual competition for binding sites cannot be excluded. To overcome these caveats, we assessed differential scanning fluorimetry with a nanoDSF device as a label-free alternative. NanoDSF monitors the changes in the intrinsic tryptophan fluorescence (ITF) resulting from alterations of the 3D-structure of proteins as a function of the temperature. Using rhinovirus A2 as a model, we demonstrate that nanoDFS is well suited for recording the temperature-dependence of conformational changes associated with viral uncoating with minute amounts of sample. We compare it with orthogonal methods and correlate the increase in viral RNA exposure with PaSTRy measurements. Importantly, nanoDSF correctly identified the thermal stabilization of RV-A2 by pleconaril, a prototypic pocket-binding antiviral compound. NanoDFS is thus a label-free, high throughput-customizable, attractive alternative for the discovery of capsid-binding compounds impacting on viral stability.

Single-Virus Tracking: From Imaging Methodologies to Virological Applications

Uncovering the mechanisms of virus infection and assembly is crucial for preventing the spread of viruses and treating viral disease. The technique of single-virus tracking (SVT), also known as single-virus tracing, allows one to follow individual viruses at different parts of their life cycle and thereby provides dynamic insights into fundamental processes of viruses occurring in live cells. SVT is typically based on fluorescence imaging and reveals insights into previously unreported infection mechanisms. In this review article, we provide the readers a broad overview of the SVT technique. We first summarize recent advances in SVT, from the choice of fluorescent labels and labeling strategies to imaging implementation and analytical methodologies. We then describe representative applications in detail to elucidate how SVT serves as a valuable tool in virological research. Finally, we present our perspectives regarding the future possibilities and challenges of SVT.

In vitro RNA release from a human rhinovirus monitored by means of a molecular beacon and chip electrophoresis

Liquid-phase electrophoresis either in the classical capillary format or miniaturized (chip CE) is a valuable tool for quality control of virus preparations and for targeting questions related to conformational changes of viruses during infection. We present an in vitro assay to follow the release of the RNA genome from a human rhinovirus (common cold virus) by using a molecular beacon (MB) and chip CE. The MB, a probe that becomes fluorescent upon hybridization to a complementary sequence, was designed to bind close to the 3′ end of the viral genome. Addition of Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), a well-known additive for reduction of bleaching and blinking of fluorophores in fluorescence microscopy, to the background electrolyte increased the sensitivity of our chip CE set-up. Hence, a fast, sensitive and straightforward method for the detection of viral RNA is introduced. Additionally, challenges of our assay will be discussed. In particular, we found that (i) desalting of virus preparations prior to analysis increased the recorded signal and (ii) the MB–RNA complex signal decreased with the time of virus storage at −70 °C. This suggests that 3′-proximal sequences of the viral RNA, if not the whole genome, underwent degradation during storage and/or freezing and thawing. In summary, we demonstrate, for two independent virus batches, that chip electrophoresis can be used to monitor MB hybridization to RNA released upon incubation of the native virus at 56 °C.

Graphical Abstract

Analysis of a common cold virus and its subviral particles by gas-phase electrophoretic mobility molecular analysis and native mass spectrometry

Gas-phase electrophoretic mobility molecular analysis (GEMMA) separates nanometer-sized, single-charged particles according to their electrophoretic mobility (EM) diameter after transition to the gas-phase via a nano electrospray process. Electrospraying as a soft desorption/ionization technique preserves noncovalent biospecific interactions. GEMMA is therefore well suited for the analysis of intact viruses and subviral particles targeting questions related to particle size, bioaffinity, and purity of preparations. By correlating the EM diameter to the molecular mass (Mr) of standards, the Mr of analytes can be determined. Here, we demonstrate (i) the use of GEMMA in purity assessment of a preparation of a common cold virus (human rhinovirus serotype 2, HRV-A2) and (ii) the analysis of subviral HRV-A2 particles derived from such a preparation. (iii) Likewise, native mass spectrometry was employed to obtain spectra of intact HRV-A2 virions and empty viral capsids (B-particles). Charge state resolution for the latter allowed its Mr determination. (iv) Cumulatively, the data measured and published earlier were used to establish a correlation between the Mr and EM diameter for a range of globular proteins and the intact virions. Although a good correlation resulted from this analysis, we noticed a discrepancy especially for the empty and subviral particles. This demonstrates the influence of genome encapsulation (preventing analytes from shrinking upon transition into the gas-phase) on the measured analyte EM diameter. To conclude, GEMMA is useful for the determination of the Mr of intact viruses but needs to be employed with caution when subviral particles or even empty viral capsids are targeted. The latter could be analyzed by native MS.

Viral uncoating is directional: exit of the genomic RNA in a common cold virus starts with the poly-(A) tail at the 3'-end

Upon infection, many RNA viruses reorganize their capsid for release of the genome into the host cell cytosol for replication. Often, this process is triggered by receptor binding and/or by the acidic environment in endosomes. In the genus Enterovirus, which includes more than 150 human rhinovirus (HRV) serotypes causing the common cold, there is persuasive evidence that the viral RNA exits single-stranded through channels formed in the protein shell. We have determined the time-dependent emergence of the RNA ends from HRV2 on incubation of virions at 56°C using hybridization with specific oligonucleotides and detection by fluorescence correlation spectroscopy. We report that psoralen UV crosslinking prevents complete RNA release, allowing for identification of the sequences remaining inside the capsid. We also present the structure of uncoating intermediates in which parts of the RNA are condensed and take the form of a rod that is directed roughly towards a two-fold icosahedral axis, the presumed RNA exit point. Taken together, in contrast to schemes frequently depicted in textbooks and reviews, our findings demonstrate that exit of the RNA starts from the 3′-end. This suggests that packaging also occurs in an ordered manner resulting in the 3′-poly-(A) tail becoming located close to a position of pore formation during conversion of the virion into a subviral particle. This directional genome release may be common to many icosahedral non-enveloped single-stranded RNA viruses.

Viral infection requires safe transfer of the viral genome from within the protective protein shell into the host cell's cytosol. For many viruses this happens after uptake into endosomes, where receptor-binding and/or the acidic pH trigger conformational modifications or disassembly of the shell, allowing the nucleic acids to escape. For example, common cold viruses are converted into subviral particles still containing the single-stranded positive sense RNA genome; subsequently, the RNA escapes into the cytoplasm, leaving behind empty capsids. We triggered this process by heating HRV2 to 56°C and found that 3′- and 5′-end emerged with different kinetics. Crosslinking prevented complete RNA egress and upon nuclease digestion only sequences derived from the 5′-end were protected. Part of the RNA remaining within the viral shell adopted a rod-like shape pointing towards one of the two-fold axes where the RNA is presumed to exit in single-stranded form. Egress thus commences with the poly-(A) tail and not with the genome-linked peptide VPg. This suggests that assembly and uncoating are well-coordinated to avoid tangling, kinetic traps, and/or simultaneous exit of the two RNA ends at different sites.

Viral quantitative capillary electrophoresis for counting and quality control of RNA viruses

The world of health care has witnessed an explosive boost to its capacity within the past few decades due to the introduction of viral therapeutics to its medicinal arsenal. As a result, a need for new methods of viral quantification has arisen to accommodate this rapid advancement in virology and associated requirements for efficiency, speed, and quality control. In this work, we apply viral quantitative capillary electrophoresis (viral qCE) to determine (i) the number of intact virus particles (ivp) in viral samples, (ii) the amount of DNA contamination, and (iii) the degree of viral degradation after sonication, vortexing, and freeze-thaw cycles. This quantification method is demonstrated on an RNA-based vesicular stomatitis virus (VSV) with oncolytic properties. A virus sample contains intact VSV particles as well as residual DNA from host cells, which is regulated by WHO guidelines, and may include some carried-over RNA. We use capillary zone electrophoresis with laser-induced fluorescent detection to separate intact virus particles from DNA and RNA impurities. YOYO-1 dye is used to stain all DNA and RNA in the sample. After soft lysis of VSV with proteinase K digestion of viral capsid and ribonucleoproteins, viral RNA is released. Therefore, the initial concentration of intact virus is calculated based on the gain of a nucleic acid peak and an RNA calibration curve. After additional NaOH treatment of the virus sample, RNA is hydrolyzed leaving residual DNA only, which is also calculated by a DNA calibration curve made by the same CE instrument. Viral qCE works in a wide dynamic range of virus concentrations from 10(8) to 10(13) ivp/mL. It can be completed in a few hours and requires minimum optimization of CE separation.

Quantum dot-aptamer nanoprobes for recognizing and labeling influenza A virus particles

The fluorescence labeling of viruses is a useful technology for virus detection and imaging. By combining the excellent fluorescence properties of quantum dots (QDs) with the high affinity and specificity of aptamers, we constructed a QD-aptamer probe. The aptamer A22, against the hemagglutinin of influenza A virus, was linked to QDs, producing the QD-A22 probe. Fluorescence imaging and transmission electron microscopy showed that the QD-A22 probe could specifically recognize and label influenza A virus particles. This QD labeling technique provides a new strategy for labeling virus particles for virus detection and imaging.

Virus analysis using electromigration techniques

We discuss the progress during the last 4 years in the analysis of viruses by electrophoresis in capillaries and microfluidic devices. The paper is the continuation of a review published in this journal in 2005 [Kremser, L., Blaas, D., Kenndler, E., Electrophoresis 2004, 25, 2282-2291]. Eighteen papers on the topic have appeared since; the majority deals with zone electrophoresis and three reports are on IEF. These methods have been applied to human rhinoviruses, poliovirus Semliki Forest virus, norovirus-like particles, and the two bacteriophages MS2 and T5. A main finding was that addition of detergents and salts to the BGEs are essential for the robustness of the CE analysis. Analyte detection was usually via UV absorbance but there are some examples where the viruses were rendered fluorescent via modification of the capsid proteins with reactive dyes and/or by non-covalent attachment of intercalating fluorescent compounds to the nucleic acids making up the viral genome. Interestingly, some viruses are permeable to small molecular mass components; this allows fluorescent dyes to diffuse into the intact virus where they attach to the nucleic acid. Release of a viral genome upon heating was also monitored by using similar methodologies. Interactions of viruses and subviral particles with antibodies, receptors, and receptor-decorated liposomes were investigated with CE methods, all by using a non-equilibrium approach (i.e. co-incubation of the components prior to CE separation). Viruses are multivalent (i.e. possess many identical surface-exposed patches) and most of them are composed of defined numbers of identical subunits. The high resolution of CE has been most remarkably demonstrated by the separation of stoichiometric complexes between virus and a distinct number of soluble recombinant receptors and revealed their concentration-dependent distribution.

Electrophoresis on a microfluidic chip for analysis of fluorescence-labeled human rhinovirus

We report the analysis of human rhinovirus serotype 2 (HRV2) on a commercially available lab-on-a-chip instrument. Due to lack of sufficient native fluorescence, the proteinaceous capsid of HRV2 was labeled with Cy5 for detection by the red laser (lambda ex 630 nm) implemented in the instrument. On the microdevice, electrophoresis of the labeled virus was possible in a BGE without stabilizing detergents, which is in contrast to conventional CE; moreover, analysis times were drastically shortened to the few 10 s range. Resolution of the sample constituents (virions, a contaminant present in all virus preparations, and excess dye) was improved upon adaptation of the separation conditions, mainly by adjusting the SDS concentration of the BGE. Purity of fractions from size-exclusion chromatography after labeling of virus was assessed, and affinity complex formation of the labeled virus with various recombinant very-low-density lipoprotein receptor derivatives differing in the number of concatenated V3 ligand binding repeats was monitored. Virus analysis on microchip devices is of particular interest for experiments with infectious material because of easy containment and disposal of samples. Thus, the employment of microchip devices in routine analysis of viruses appears to be exceptionally attractive.

Imaging poliovirus entry in live cells

Viruses initiate infection by transferring their genetic material across a cellular membrane and into the appropriate compartment of the cell. The mechanisms by which animal viruses, especially nonenveloped viruses, deliver their genomes are only poorly understood. This is due in part to technical difficulties involved in direct visualization of viral gene delivery and to uncertainties in distinguishing productive and nonproductive pathways caused by the high particle-to–plaque forming unit ratio of most animal viruses. Here, we combine an imaging assay that simultaneously tracks the viral capsid and genome in live cells with an infectivity-based assay for RNA release to characterize the early events in the poliovirus (PV) infection. Effects on RNA genome delivery from inhibitors of cell trafficking pathways were probed systematically by both methods. Surprisingly, we observe that genome release by PV is highly efficient and rapid, and thus does not limit the overall infectivity or the infection rate. The results define a pathway in which PV binds to receptors on the cell surface and enters the cell by a clathrin-, caveolin-, flotillin-, and microtubule-independent, but tyrosine kinase- and actin-dependent, endocytic mechanism. Immediately after the internalization of the virus particle, genome release takes place from vesicles or tightly sealed membrane invaginations located within 100–200 nm of the plasma membrane. These results settle a long-lasting debate of whether PV directly breaks the plasma membrane barrier or relies on endocytosis to deliver its genome into the cell. We expect this imaging assay to be broadly applicable to the investigation of entry mechanisms for nonenveloped viruses.

During travel between hosts, the genome of a virus is well protected by the viral capsid and/or envelope. After binding specifically to target cells, the virus particles enter cells by hijacking cell trafficking pathways and then deliver the viral genome into the appropriate compartment of the cell where it directs the production of progeny virus particles. How nonenveloped viruses, such as poliovirus, enter target cells is not well understood. Here, we produced fully infectious poliovirus with both genome and capsid specifically labeled by fluorescent dyes. We could then use real-time fluorescent microscopy to follow single virus particles during infection, to define how they enter cells and to determine when and where in the cell the genome gets released. We have complemented the microscopic studies with virological assays, which demonstrate that the pathways observed by microscopy are productive. We show that poliovirus enters live cells in a process that requires energy, an intact actin cytoskeleton, and cell signaling pathways, but does not depend on the well-known markers of endocytic pathways. We show that after internalization, the genome release is surprisingly efficient and occurs from vesicles that are very close to the cell surface. Our experiments offer new insights into the early steps of poliovirus infection, and describe methods that can be used for a wide variety of other viruses.

Combining an imaging assay that simultaneously tracks the viral capsid and genome in live cells with an infectivity-based biological assay for RNA release, the authors settle a long-lasting debate on the nature of poliovirus entry into the host cell.

Capillary electrophoresis of viruses, subviral particles and virus complexes

CZE and CIEF were so far applied to the analysis of tobacco mosaic virus, Semliki forest virus, human rhinovirus, adenovirus, norovirus and the bacteriophages T5 and MS2. The concentration of viral or subviral particles, of capsid proteins and viral genomes were determined, their electrophoretic mobilities and pI values were measured and bioaffinity reactions between viruses and antibodies, antibody fragments and receptor fragments were assessed. The role of detergents added to the BGE to obtain reproducible electrophoretic conditions was elucidated. The analytes were detected via their UV-absorbance or via fluorescence after derivatization of the viral capsid, the nucleic acid, or both. A new dimension to the detection is added by the possibility of making use of the viral infectivity. At least in theory, this allows for the unequivocal identification of a single infectious virus particle after collection at the capillary outlet. This review summarizes the 25 papers so far published on this topic.

Capillary electrophoresis of affinity complexes between subviral 80S particles of human rhinovirus and monoclonal antibody 2G2

Human rhinoviruses (HRVs), the main etiologic agents of the common cold, transform into subviral B- or 80S particles (they sediment at 80S upon sucrose density gradient centrifugation) during infection and, in vitro, upon exposure to a temperature between 50 and 56 degrees C. With respect to the native virion they lack the genomic RNA and the viral capsid protein VP4. 80S particles are unstable and easily disintegrate into their components, VP1, VP2, and VP3 in buffers containing SDS. However, this detergent was found to be a necessary constituent of the BGE for the analysis of these viruses and their complexes with receptors and antibodies by CE. We here demonstrate that dodecylpoly(ethyleneglycol ether) (D-PEG) a nonionic detergent, is suitable for analysis of subviral particles as it preserves their integrity, in contrast to SDS. Electrophoresis of the 80S particles in borate buffer (pH 8.3, 100 mM) containing 10 mM D-PEG resulted in a well-defined electrophoretic peak. The identity of the peak was confirmed, among other means, by complexation with mAb 2G2, which recognizes a structural epitope exclusively present on subviral particles but not on native virus. Upon incubation of the 80S particles with mAb 2G2 the peak disappeared, but a new peak, attributed to the antibody complex emerged. The separation system allowed following the time course of the transformation of intact HRV serotype 2 into 80S particles upon incubation at temperatures between 40 and 65 degrees C. We also demonstrate that subviral particles derived from HRV2 labeled with the fluorescence dyes FITC or Cy3.5 were stable in the separation system containing D-PEG. Dye-modified particles were still recognized by mAb 2G2, suggesting that the exposed lysines that are derivatized by the reagent do not form part of the epitope of the antibody.

Recent applications of affinity interactions in capillary electrophoresis

Systems biology depends on a comprehensive assignment and characterization of the interactions of proteins and polypeptides (functional proteomics) and of other classes of biomolecules in a given organism. High‐capacity screening methods are in place for ligand capture and interaction screening, but a detailed dynamic characterization of molecular interactions under physiological conditions in efficiently separated mixtures with minimal sample consumption is presently provided only by electrophoretic interaction analysis in capillaries, affinity CE (ACE). This has been realized in different fields of biology and analytical chemistry, and the resulting advances and uses of ACE during the last 2.5 years are covered in this review. Dealing with anything from small divalent metal ions to large supramolecular assemblies, the applications of ACE span from low‐affinity binding of broad specificity being exploited in optimizing selectivity, e.g., in enantiomer analysis to miniaturized affinity technologies, e.g., for fast processing immunoassay. Also, approaches that provide detailed quantitative characterization of analyte–ligand interaction for drug, immunoassay, and aptamer development are increasingly important, but various approaches to ACE are more and more generally applied in biological research. In addition, the present overview emphasizes that distinct challenges regarding sensitivity, parallel processing, information‐rich detection, interfacing with MS, analyte recovery, and preparative capabilities remain. This will be addressed by future technological improvements that will ensure continuing new applications of ACE in the years to come.

Rhinovirus-stabilizing activity of artificial VLDL-receptor variants defines a new mechanism for virus neutralization by soluble receptors

Members of the low-density lipoprotein receptor family possess various numbers of ligand binding repeats that non-equally contribute to binding of minor group human rhinoviruses. Using an artificial concatemer of five copies of repeat 3 of the human very-low density lipoprotein receptor, we demonstrate protection of HRV2 against low-pH mediated uncoating and inhibition of penetration of an RNA-specific fluorescent dye into the intact virion. This indicates that the recombinant receptor inhibits viral breathing and irreversible conformational modifications of the capsid that precede RNA release, providing a new mechanism for rhinovirus neutralization by soluble receptor molecules.