Structural and functional analysis of protective antibodies targeting the threefold plateau of enterovirus 71

Enterovirus 71 (EV71)-neutralizing antibodies correlate with protection and have potential as therapeutic agents. We isolate and characterize a panel of plasmablast-derived monoclonal antibodies from an infected child whose antibody response focuses on the plateau epitope near the icosahedral 3-fold axes. Eight of a total of 19 antibodies target this epitope and three of these potently neutralize the virus. Representative neutralizing antibodies 38-1-10A and 38-3-11A both confer effective protection against lethal EV71 challenge in hSCARB2-transgenic mice. The cryo-electron microscopy structures of the EV71 virion in complex with Fab fragments of these potent and protective antibodies reveal the details of a conserved epitope formed by residues in the BC and HI loops of VP2 and the BC and HI loops of VP3 spanning the region around the 3-fold axis. Remarkably, the two antibodies interact with the epitope in quite distinct ways. These plateau-binding antibodies provide templates for promising candidate therapeutics.

Bioorthogonal Metabolic Labeling Utilizing Protein Biosynthesis for Dynamic Visualization of Nonenveloped Enterovirus 71 Infection

Bioorthogonal metabolic labeling through the endogenous cellular metabolic pathways (e.g., phospholipid and sugar) is a promising approach for effectively labeling live viruses. However, it remains a big challenge to label nonenveloped viruses due to lack of host-derived envelopes. Herein, a novel bioorthogonal labeling strategy is developed utilizing protein synthesis pathway to label and trace nonenveloped viruses. The results show that l-azidohomoalanine (Aha), an azido derivative of methionine, is more effective than azido sugars to introduce azido motifs into viral capsid proteins by substituting methionine residues during viral protein biosynthesis and assembly. The azide-modified EV71 (N₃-EV71) particles are then effectively labeled with dibenzocyclooctyl (DBCO)-functionalized fluorescence probes through an in situ bioorthogonal reaction with well-preserved viral infectivity. Dual-labeled imaging clearly clarifies that EV71 virions primarily bind to scavenger receptors and are internalized through clathrin-mediated endocytosis. The viral particles are then transported into early and late endosomes where viral RNA is released in a low-pH dependent manner at about 70 min postinfection. These results first reveal viral trafficking and uncoating mechanisms, which may shed light on the pathogenesis of EV71 infection and contribute to antiviral drug discovery.

Hand-foot-and-mouth disease virus receptor KREMEN1 binds the canyon of Coxsackie Virus A10

Coxsackievirus A10 (CV-A10) is responsible for an escalating number of severe infections in children, but no prophylactics or therapeutics are currently available. KREMEN1 (KRM1) is the entry receptor for the largest receptor-group of hand-foot-and-mouth disease causing viruses, which includes CV-A10. We report here structures of CV-A10 mature virus alone and in complex with KRM1 as well as of the CV-A10 A-particle. The receptor spans the viral canyon with a large footprint on the virus surface. The footprint has some overlap with that seen for the neonatal Fc receptor complexed with enterovirus E6 but is larger and distinct from that of another enterovirus receptor SCARB2. Reduced occupancy of a particle-stabilising pocket factor in the complexed virus and the presence of both unbound and expanded virus particles suggests receptor binding initiates a cascade of conformational changes that produces expanded particles primed for viral uncoating.

Small molecules targeting coxsackievirus A16 capsid inactivate viral particles and prevent viral binding

Coxsackievirus A16 (CVA16) is an etiologic agent of hand, foot, and mouth disease (HFMD) that affects young children, and although typically self-limited, severe complications, and fatal cases have been reported. Due to the lack of specific medication and vaccines against CVA16, there is currently a need to develop effective antivirals to better control CVA16 infections in epidemic areas. In this study, we identified the tannins chebulagic acid (CHLA) and punicalagin (PUG) as small molecules that can efficiently disrupt the CVA16 infection of human rhabdomyosarcoma cells. Both compounds significantly reduced CVA16 infectivity at micromolar concentrations without apparent cytotoxicity. A mechanistic analysis revealed that the tannins particularly targeted the CVA16 entry phase by inactivating cell-free viral particles and inhibiting viral binding. Further examination by molecular docking analysis pinpointed the targets of the tannins in the fivefold axis canyon region of the CVA16 capsid near the pocket entrance that functions in cell surface receptor binding. We suggest that CHLA and PUG are efficient antagonists of CVA16 entry and could be of value as antiviral candidates or as starting points for developing molecules to treat CVA16 infections.

Prokaryotic expression and identification of scavenger receptor B2

There is still no effective clinical antiviral drug against human enterovirus 71 (EV71) infection, which causes hand, foot and mouth disease (HFMD) in children. Scavenger receptor class B member 2 (SCARB2) is an important receptor of EV71 as it plays a vital role in the early steps of viral infection. In this study, recombinant SCARB2 protein was expressed and purified in a prokaryotic expression system, and was identified by western blot with a monoclonal antibody and mass spectrometry analysis. Detection of the sera from mice immunized with the recombinant SCARB2 protein using ELISA and western blot showed good immunogenicity of the recombinant protein. Furthermore, in the neutralization test cytopathic effect was significantly decreased when EV71 was incubated with the immune sera before infection. In summary, the SCARB2 protein was expressed successfully, and the immune sera showed obvious antiviral effect against EV71. This study provides useful information about the interaction mechanism between SCARB2 and EV71, and is also helpful for further clinical treatment research of HFMD.

Exploiting the Anti-Aggregation of Gold Nanostars for Rapid Detection of Hand, Foot, and Mouth Disease Causing Enterovirus 71 Using Surface-Enhanced Raman Spectroscopy

Enterovirus 71 (EV71) is a major public health threat that requires rapid point-of-care detection. Here, we developed a surface-enhanced Raman spectroscopy (SERS)-based scheme that utilized protein-induced aggregation of colloidal gold nanostars (AuNS) to rapidly detect EV71 without the need for fabricating a solid substrate, Raman labels or complicated sample handling. We used AuNS (hydrodynamic diameter, DH of 105.12 ± 1.13 nm) conjugated to recombinant scavenger receptor class B, member 2 (SCARB2) protein with known affinity to EV71. In the absence of EV71, AuNS-SCARB2 aggregated in biological media and produced four enhanced Raman peaks at 390, 510, 670, and 910 cm-1. In the presence of EV71, the three peaks at 510, 670, and 910 cm-1 disappeared, while the peak at 390 cm-1 diminished in intensity as the virus bound to AuNS-SCARB2 and prevented them from aggregation. These three peaks (510, 670, and 910 cm-1) were potential markers for specific detection of EV71 as their disappearance was not observable with a different dengue virus (DENV) as our control. Furthermore, the Raman measurements from colloidal SERS were more sensitive in probing the aggregation of AuNS-SCARB2 for detecting the presence of EV71 in protein-rich samples compared to UV-vis spectrum measurements. With this facile "anti-aggregation" approach, we were able to detect EV71 in protein-rich biological medium within 15 min with reasonable sensitivity of 107 pfu/mL and minimal sample preparation, making this translatable for point-of-care applications.

[The Complete Sequence Analysis of 18 Strains of Coxsackievirus A6 in Guangdong Province of China]

In this study, we examined the complete genome of coxsackievirus A6 (CVA6) from hand, foot, and mouth disease in Guangdong Province from 2013,and explored the genetic similarities and differences in epidemic and non-epidemic stains of CVA6.Eighteen strains of CVA6 were included in complete genome sequencing, and the sequences were subject to phylogenetic analysis,sequence alignment analysis and genetic recombination analysis using the software DNASTAR6.0,MEGA5.2and SimPlot3.5.1.The results showed that the complete genome of 18 Guangdong CVA6strains ranged from 7390bp to 7392bp.No insertions or deletions were detected in the coding region. There were several insertions and deletions in 5′UTR and 3′UTR.Phylogenetic analysis indicated that the nucleotide and amino acid sequence identity between the 18 complete genomes were 90.5%-99.6% and 97.5%-99.9%,respectively.The strains isolated in2013 could be further divided into two clusters, III and IV, while the strains isolated in 2011 were only present in the IV cluster. Genetic recombination analysis revealed that the Guangdong representative strain of CVA6,GD870/2013,had gene recombination in the P2 and P3regions,while the GD839/2013 strain did not show obvious genetic recombination. Genome-wide analysis of CVA6 revealed that there are two possible transmitted chains, III and IV, in epidemic strains from Guangdong Province in 2013.The transmitted chain Ⅲ originated from the strain with genetic recombination in the P2 and P3regions,whichwas completely different from the chain IV. Transmission of chain IV of CVA6 was only observed in the nonepidemic 2011 strain.

Cooperative effect of the VP1 amino acids 98E, 145A and 169F in the productive infection of mouse cell lines by enterovirus 71 (BS strain)

Enterovirus 71 (EV71) is a neurotrophic virus that causes hand, foot and mouth disease (HFMD) and occasional neurological infection among children. It infects primate cells but not rodent cells, primarily due to the incompatibility between the virus and the expressed form of its receptor, scavenger receptor class B member 2 (SCARB2) protein, on rodent cells (mSCARB2). We previously generated adapted strains (EV71:TLLm and EV71:TLLmv) that were shown to productively infect primate and rodent cell lines and whose genomes exhibited a multitude of non-synonymous mutations compared with the EV71:BS parental virus. In this study, we aimed to identify mutations that are necessary for productive infection of murine cells by EV71:BS. Using reverse genetics and site-directed mutagenesis, we constructed EV71 infectious clones with specific mutations that generated amino acid substitutions in the capsid VP1 and VP2 proteins. We subsequently assessed the infection induced by clone-derived viruses (CDVs) in mouse embryonic fibroblast NIH/3T3 and murine neuroblastoma Neuro-2a cell lines. We found that the CDV:BS-VP1(K98E,E145A,L169F) with three substitutions in the VP1 protein-K98E, E145A and L169F-productively infected both mouse cell lines for at least three passages of the virus in murine cells. Moreover, the virus gained the ability to utilize the mSCARB2 protein to infect murine cell lines. These results demonstrate that the three VP1 residues cooperate to effectively interact with the mSCARB2 protein on murine cells and permit the virus to infect murine cells. Gain-of-function studies similar to the present work provide valuable insight into the mutational trajectory required for EV71 to infect new host cells previously non-susceptible to infection.

Structure Elucidation of Coxsackievirus A16 in Complex with GPP3 Informs a Systematic Review of Highly Potent Capsid Binders to Enteroviruses

The replication of enterovirus 71 (EV71) and coxsackievirus A16 (CVA16), which are the major cause of hand, foot and mouth disease (HFMD) in children, can be inhibited by the capsid binder GPP3. Here, we present the crystal structure of CVA16 in complex with GPP3, which clarifies the role of the key residues involved in interactions with the inhibitor. Based on this model, in silico docking was performed to investigate the interactions with the two next-generation capsid binders NLD and ALD, which we show to be potent inhibitors of a panel of enteroviruses with potentially interesting pharmacological properties. A meta-analysis was performed using the available structural information to obtain a deeper insight into those structural features required for capsid binders to interact effectively and also those that confer broad-spectrum anti-enterovirus activity.

Hydrated silica exterior produced by biomimetic silicification confers viral vaccine heat-resistance

Heat-lability is a key roadblock that strangles the widespread applications of many biological products. In nature, archaeal and extremophilic organisms utilize amorphous silica as a protective biomineral and exhibit considerable thermal tolerance. Here we present a bioinspired approach to generate thermostable virus by introducing an artificial hydrated silica exterior on individual virion. Similar to thermophiles, silicified viruses can survive longer at high temperature than their wild-type relatives. Virus inactivation assays showed that silica hydration exterior of the modified virus effectively prolonged infectivity of viruses by ∼ 10-fold at room temperature, achieving a similar result as that obtained by storing native ones at 4 °C. Mechanistic studies indicate that amorphous silica nanoclusters stabilize the inner virion structure by forming a layer that restricts molecular mobility, acting as physiochemical nanoanchors. Notably, we further evaluate the potential application of this biomimetic strategy in stabilizing clinically approved vaccine, and the silicified polio vaccine that can retain 90% potency after the storage at room temperature for 35 days was generated by this biosilicification approach and validated with in vivo experiments. This approach not only biomimetically connects inorganic material and living virus but also provides an innovative resolution to improve the thermal stability of biological agents using nanomaterials.

[Research methods in protein-protein and protein-nucleic acid interactions and application in the study of human enterovirus A71]

Methods for analyses of protein-protein interactions include: yeast two hybrid (Y2H), phage dis- play (PD), co-immunoprecipitation (Co-IP), glutathione S-transferase pull-down (GST pull-down), cellular co-localization, far-western blotting, virus overlay protein binding assay (VOPBA), surface plasmon resonance (SPR), and fluorescence resonance energy transfer (FRET). Technologies for the detection of protein-nucleic acid interactions include: yeast one hybrid (Y1H), chromatin immunoprecipitation (ChIP), electrophoretic mobility shift assay (EMSA), Southwestern blotting, reporter gene, Co-IP, GST pull-down, and PD. These methods are often used in the study of the human enterovirus A71 (EV-A71) by our research team. Reviews in the Chinese literature in this field are lacking, so we reviewed applications of these methods in the study of EV-A71. This review may impart important knowledge in the research of other viruses with regard to protein-protein and protein-nucleic acid interactions.

The identification and characterization of nucleic acid chaperone activity of human enterovirus 71 nonstructural protein 3AB

Human enterovirus 71 (EV71) belongs to the genus Enterovirus in the family Picornaviridae and has been recognized as one of the most important pathogens that cause emerging infectious disease. Despite of the importance of EV71, the nonstructural protein 3AB from this virus is little understood for its function during EV71 replication. Here we expressed EV71 3AB protein as recombinant protein in a eukaryotic expression system and uncovered that this protein possesses a nucleic acid helix-destabilizing and strand annealing acceleration activity in a dose-dependent manner, indicating that EV71 3AB is a nucleic acid chaperone protein. Moreover, we characterized the RNA chaperone activity of EV71 3AB, and revealed that divalent metal ions, such as Mg²⁺ and Zn²⁺, were able to inhibit the RNA helix-destabilizing activity of 3AB to different extents. Moreover, we determined that 3B plus the last 7 amino acids at the C-terminal of 3A (termed 3B+7) possess the RNA chaperone activity, and five amino acids, i.e. Lys-80, Phe-82, Phe-85, Tyr-89, and Arg-103, are critical and probably the active sites of 3AB for its RNA chaperone activity. This report reveals that EV71 3AB displays an RNA chaperone activity, adds a new member to the growing list of virus-encoded RNA chaperones, and provides novel knowledge about the virology of EV71.

[Recombination analysis of enterovirus 71 strain isolated in Guangzhou, 2009]

To describe the recombination features of human enterovirus 71 strain Guangzhou09 isolated in Guangzhou in 2009, the complete nucleotide sequences of Guangzhou09 were analyzed by various of bioinformatics software. Phylogenetic analysis based on P1, P2 and P3 regions indicated that recombination occurred between EV71 and CVA4. Phylogenetic, similarity plot and bootscan analysis further revealed the recombination between EV71 genotype C strain Shanghai-FJ713317 and CVA4 strain HQ728260 at region 2B was close to the nucleotide position 4 027. This represents the first evidence for intertypic recombination between EV71 subtype C4 and CVA4 in Guangzhou.

Novel substituted heteroaromatic piperazine and piperidine derivatives as inhibitors of human enterovirus 71 and coxsackievirus a16

A series of substituted heteroaromatic piperazine and piperidine derivatives were found through virtual screening based on the structure of human enterovirus 71 capsid protein VP1. The preliminary biological evaluation revealed that compounds 8e and 9e have potent activity against EV71 and Coxsackievirus A16 with low cytotoxicity.

[Genetic characteristics of enterovirus 71 VP1 and epidemiology of hand-foot-mouth disease in Xinxiang in 2011]

The study was performed to examine the enterovirus 71(EV71) VP1 genetic feature and the epidemiology of hand-foot-mouth disease (HFMD) in Xinxiang in 2011. Real-time RT-PCR was used for the detection of Pan-enterovirus, Coxsackievirus A 16(CA16) and EV71 from stool specimens of HFMD. The VP1 region was amplified from 10 EV71 positive samples and the products were sequenced. EV71 genotypes were characterized by homology and phylogenetic tree analyses. Additionally, epidemic data of Xinxiang HFMD in 2011 was analyzed. The results revealed that 73% of the specimens from severe cases were determined as EV71 positive, which was significantly higher than CA16-positive ones (19%) (P < 0.01). Ten EV71 strains isolated in Xinxiang belonged to C4a cluster of sub-genotype C4, with 2.8% nucleotide and 0.9% amino acid sequences divergence among them. At position 170 in VP1 gene, an alanine(A) was predominant in 9 isolates, while a valine(V) residue was observed in one isolate. Compared to the representative C4a strains which were closely related to Xinxiang isolates, the amino acid variations of the pre-dominant Xinxiang strains generally occurred at position 292, threonine --> alanine (T --> A). A total of 1118 HFMD cases were reported in Xinxiang in 2011, and 92% of them were younger than 3 years old; the incidence rate peaked in April and December, suggesting that it is very necessary to strengthen HFMD prevention and control even in cold weather.

[Expression of structural protein VP1 of enterovirus 71 in E.coli and preparation of anti-VP1 monoclonal antibodies]

AIM

To express recombinant structural protein VP1 of enterovirus 71 (EV71) in E.coli and prepare anti-VP1 monoclonal antibodies (mAbs).

METHODS

With P1 gene as a template, EV71 VP1 gene was amplified by PCR and cloned into the expression vector pET-32a(+). After transformation into E.coli TG1, the positive clones were screened and sequenced. The recombinant plasmid was then transformed into BLgold (DE3) and the recombinant protein in inclusion bodies was induced by IPTG and detected by SDS-PAGE. After the inclusion bodies were solubilized with 6 mol/L guanidine hydrochloride, we purified VP1 protein using Ni-NTA affinity chromatography, and then immunized the mice with it to prepare the mAbs against VP1 protein.

RESULTS

Recombinant VP1 protein was expressed in E.coli. We obtained totally 24 VP1 monoclonal hybridoma cell strains, of which one was EV71 positive determined by Western blotting and five were positive for IFA.

CONCLUSION

These mAbs are valuable reagents for the development of new vaccines and detection kits for EV71.

Human SCARB2-dependent infection by coxsackievirus A7, A14, and A16 and enterovirus 71

Human enterovirus species A (HEV-A) consists of at least 16 members of different serotypes that are known to be the causative agents of hand, foot, and mouth disease (HFMD), herpangina, and other diseases, such as respiratory disease and polio-like flaccid paralysis. Enterovirus 71 (EV71) and coxsackievirus A16 (CVA16) are the major causative agents of HFMD. CVA5, CVA6, CVA10, and CVA12 mainly cause herpangina or are occasionally involved with sporadic cases of HFMD. We have previously shown that human scavenger receptor class B, member 2 (SCARB2) is a cellular receptor for EV71 and CVA16. Using a large number of clinical isolates of HEV-A, we explored whether all clinical isolates of EV71 and other serotypes of HEV-A infected cells via SCARB2. We tested this possibility by infecting L-SCARB2 cells, which are L929 cells expressing human SCARB2, by infecting human RD cells that had been treated with small interfering RNAs for SCARB2 and by directly binding the viruses to a soluble SCARB2 protein. We showed that all 162 clinical isolates of EV71 propagated in L-SCARB2 cells, suggesting that SCARB2 is the critical receptor common to all EV71 strains. In addition, CVA7, CVA14, and CVA16, which are most closely related to each other, also utilized SCARB2 for infection. EV71, CVA14, and CVA16 are highly associated with HFMD, and EV71 and CVA7 are occasionally associated with neurological diseases, suggesting that SCARB2 plays important roles in the development of these diseases. In contrast, another group of viruses, such as CVA2, CVA3, CVA4, CVA5, CVA6, CVA8, CVA10, and CVA12, which are relatively distant from the EV71 group, is associated mainly with herpangina. None of these clinical isolates infected via the SCARB2-dependent pathway. HEV-A viruses can be divided into at least two groups depending on the use of SCARB2, and the receptor usage plays an important role in developing the specific diseases for each group.

Crystal structures of enterovirus 71 3C protease complexed with rupintrivir reveal the roles of catalytically important residues

EV71 is the primary pathogenic cause of hand-foot-mouth disease (HFMD), but an effective antiviral drug currently is unavailable. Rupintrivir, an inhibitor against human rhinovirus (HRV), has potent antiviral activities against EV71. We determined the high-resolution crystal structures of the EV71 3C(pro)/rupintrivir complex, showing that although rupintrivir interacts with EV71 3C(pro) similarly to HRV 3C(pro), the C terminus of the inhibitor cannot accommodate the leaving-group pockets of EV71 3C(pro). Our structures reveal that EV71 3C(pro) possesses a surface-recessive S2' pocket that is not present in HRV 3C(pro) that contributes to the additional substrate binding affinity. Combined with mutagenic studies, we demonstrated that catalytic Glu71 is irreplaceable for maintaining the overall architecture of the active site and, most importantly, the productive conformation of catalytic His40. We discovered the role of a previously uncharacterized residue, Arg39 of EV71 3C(pro), that can neutralize the negative charge of Glu71, which may subsequently assist deprotonation of His40 during proteolysis.

[Sequence and antigenicity analysis for VP4s of EV71 strains isolated from Children in Beijing]

In order to learn about the correlation between the sequences of VP4 of EV71 and clinical symptoms of patients and analyze the antigenicity of VP4 of EV71, as well as the cross-reactivity with VP4 of CA16, the sequences of VP4 gene from 10 EV71 strains isolated from infants and children with hand, foot and mouth diseases (HFMD) during 2007 to 2009 were determined through standard molecular cloning protocols, and the results were analyzed by EditSeq and MegAlign of DNAStar. Full-length genes of VP4s of EV71 and CA16 were amplified from virus isolates and expressed in E. coli. Then the expressed VP4s were used as antigens to detect IgG antibody in 189 sera samples from people taking health check up and patients of non-HFMD by Western-Blot. They were also used to detect IgM antibody in 14 of sera samples from infants and children with EV71 infection and 12 of sera samples from those with CA16 infection. The nucleotides identities among these 10 sequences of VP4s isolated in our lab were 94.20% - 100.00% and the deduced amino acids were identical. There was no consistent divergence between the sequences of serious cases and those from general HFMD cases. Phylogenetic analysis based on VP4s indicated that these 10 VP4s of EV71 belonged to C4. The nucleotide identities between EV71 VP4 (s67) and CA16 VP4 (s401) was 69.60% and the deduced amino acids identities was 78.60%. In the detection of IgG, the sera-positive rate for EV71 VP4 was 38.10% and the sera-positive rate of CA16 VP4 was 58.20%. The difference in the sera-positive rate between them was significant (chi2 = 15.30, P < 0.01), suggesting that the expressed VP4s of EV71 and CA16 were of good antigenicity and not cross-reactive. There was no positive reaction detected for IgM against VP4s for EV71 or CA16. The data from this study reveal important information for the further study of EV71.

[Analysis on the preference of synonymous codon in VP1 nucleotide sequence of the EV71 based on RSCU method]

Based on RSCU method and by analyzing the preference of codon usage in VP1 nucleotide sequences of EV71 isolated in Chinese mainland and Taiwan region from 1998 to 2008, it is clear that there is an obvious time discrimination in RSCU calculated from EV71 VP1 strain between two different regions of China and it is more obvious in Taiwan region, therefore, according to the diversity of RSCU, the years can be divided into 2 intervals in Chinese mainland and 4 intervals in Taiwan region, especially, the number of intervals in one region have a positive co-relation with the activity of variation of the EV71 in the same region. The change of the preference of codon usage in VP1 nucleotide sequences of EV71 can significantly embody the Variation of the EV71, so we can make use of the analysis on preference of codon usage in VP1 nucleotide sequences of EV71 to predict the possible variation trend of the EV71.

[Genetic characterization of VP4-VP2 of two coxsackievirus A4 isolated from patients with hand, foot and mouth disease]

OBJECTIVE

To study the genetic characteristic of VP4-VP2 of Coxsackievirus A4 (CVA4) isolated from clinical specimens of patients with Hand, foot and mouth disease (HFMD) in Gansu in 2008.

METHODS

Two clinical samples were collected from HFMD patients in outpatient service, and then viral isolation was performed by inoculating RD cells. VP4-VP2 region of two viral isolates were amplified by using reverse transcription-polymerase chain reaction methods, and then the PCR products were sequenced; molecular typing was used to identify the serotype of these two viral isolates. Finally phylogenetic tree was constructed among these two Gansu viral isolates and 16 CVA4 strains downloaded from GenBank database.

RESULTS

Two Viruses were isolated from the clinical specimens collected from two HFMD patients by inoculating RD cells, and were identified as CVA4 by using molecular typing methods. The homology of the nucleotide sequences in VP4-VP2 region between the two Gansu CVA4 strains was 94.6%, and the homology of the amino acid sequences was 100%. Compared with the prototype strain of CVA4 (Strain High Point/USA/1948), the homologies of nucleotide sequences and amino acid sequences were 85.5%-85.8% and 99.3%, respectively. It revealed that two Gansu CVA4 strains lie in the independence group.

CONCLUSION

Compared with CVA4 strains isolated in Japan and Mongolia downloaded from GenBank database, two Gansu CVA4 were found to have great difference on VP4-VP2 region, and phylogenetic analysis revealed that they belong to an independence evolution lineage.