A simple screening assay for receptor switching of avian influenza viruses

Evolution and mammalian adaptation of H3 and H10 subtype avian influenza viruses in wild birds in Yancheng Wetland of China

Wild birds play a critical role in avian influenza virus (AIV) ecology and some outbreaks of avian influenza in human originate from wild birds, suggesting that epidemiological surveillance and interspecies-transmission analysis of AIVs in wild birds are critical. Since 2019, we have performed sampling in Yancheng Wetland along the East Asian-Australasian Flyway. Totally, 2054 fecal swabs were collected and one H3N8, two H3N1, one H10N8, and three H10N1 were isolated. Three H3 gene of AIVs we isolated belonged to Eurasian lineage, but the four H10 gene clustered into North American lineage. What's more, the H3 and the foreign H10 gene had generated novel reassortants in Yancheng wetland. Receptor binding assay indicated that nearly all strains, except D369/H10N1, presented a dual receptor-binding profile and bound to avian-type receptor preferentially. In animal experiment, all isolates could infect mice without prior adaptation and induce histopathological changes in mice lungs, moreover, all H3 subtype AIVs obviously triggered weight loss of mice. In addition to lung and turbinate, D322/H3N1, D338/H3N8, D211/H10N8 and D266/H10N1 could spread to brain and kidney or liver or spleen, showing a wider range of tissue tropism. Multiple mutants associated with mammalian adaptation were also detected in all isolates according to molecular analysis. These findings revealed that H3 and H10 AIVs circulating in wild birds in Yancheng Wetland underwent complex reassortment and increased mammalian adaptation, which highlighted the necessity to monitor the diverse reassortment of AIVs in wild birds and evaluate the risks of H3 and H10 viruses to human health.

Influenza A (H6N6) viruses isolated from chickens replicate in mice and human lungs without prior adaptation

The H6H6 subtype avian influenza virus (AIV) is currently prevalent in wild birds and poultry. Its host range has gradually expanded to mammals, such as swines. Some strains have even acquired the ability to bind to human-like SAα-2,6 Gal receptors, thus increasing the risk of animal to human transmission. To investigate whether the H6N6 AIV can overcome interspecies barriers from poultry to mammals and even to humans, we have assessed the molecular characteristics, receptor-binding preference, replication in mice and human lungs of three chicken-originated H6N6 strains. Among these, the A/CK/Zhangzhou/346/2014 (ZZ346) virus with the P186T, H156R, and S263G mutations of the hemagglutinin molecule showed the ability to bind to avian-like SAα-2,3 Gal and human-like SAα-2,6 Gal receptors. Moreover, H6N6 viruses, especially the ZZ346 strain, could replicate and infect mice and human lungs. Our study showed the H6N6 virus binding to both avian-like and human-like receptors, confirming its ability to cross the species barrier to infect mice and human lungs without prior adaptation. This study emphasizes the importance of continuous and intense monitoring of the H6N6 evolution in terrestrial birds.

Amino Acid Substitutions N123D and N149D in Hemagglutinin Molecule Enhance Immunigenicity of Live Attenuated Influenza H7N9 Vaccine Strain in Experiment

We compared three cold-adapted live attenuated influenza vaccine strains prepared by reverse genetics methods on the basis of master donor virus A/Leningrad/134/17/57 and influenza H7N9 strains A/Anhui/1/2013 and A/Shanghai/1/2013. Two strains based on A/Anhui/1/2013 differed by amino acid positions 123 and 149 in HA1 (123N/149N; 123D/149D). All strains efficiently replicated in developing chicken embryos; A/Shanghai/1/2013-based strain and A/Anhui/1/2013-123N/149N variant were characterized by reduced replication in MDCK cells. Strains based on A/Anhui/1/2013 virus agglutinated erythrocytes with α2,3- and α2,6-linked sialic acid residues, whereas strain A/Shanghai/1/2013 only α2,3. In experiments with BALB/c mice, Anhui-123D/149D strain was most immunogenic and induced high crossreactive humoral immune response, therefore it can be recommended as the model virus for the construction of recombinant vector vaccines based on live attenuated influenza vaccine.

Isolation and characterization of novel reassortant H6N1 avian influenza viruses from chickens in Eastern China

Background

The H6N1 subtype of avian influenza viruses (AIVs) can infect people with an influenza-like illness; the H6N1 viruses possess the ability for zoonotic transmission from avians into mammals, and possibly pose a threat to human health.

Methods

In 2017, live poultry markets (LPMs) in Zhejiang Province were surveyed for AIVs. To better understand the genetic relationships between these strains from Eastern China and other AIVs, all gene segments of these strains were sequenced and compared with sequences available in GenBank. In this study, we analyzed the receptor-binding specificity, antigenic characteristics, and pathogenicity of these two H6N1 viruses.

Results

In 2017, two H6N1 AIVs were isolated from chickens during surveillance for AIVs in LPMs in Eastern China. Phylogenetic analysis showed that these strains shared genetic characteristics from H6, H10, H1, and H4 AIVs found in ducks and wild birds in East Asia. These AIV strains were able to replicate in mice without prior adaptation.

Conclusions

In this study, we report the discovery of new strains of H6N1 viruses from chickens with novel gene reassortments. Our results suggest that these chickens play an important role generating novel reassortments in AIVs, and emphasize the need for continued surveillance of AIV strains circulating in poultry.

Electronic supplementary material

The online version of this article (10.1186/s12985-018-1063-y) contains supplementary material, which is available to authorized users.

Molecular characterization of H10 subtype avian influenza viruses isolated from poultry in Eastern China

In recent years, avian-origin H10 influenza viruses have proved capable of infecting human beings, and they pose a potential public health threat. Seven H10 avian influenza viruses (AIVs), H10N3 (n = 2), H10N7 (n = 1), and H10N8 (n = 4), were isolated from chickens in Zhejiang Province, Eastern China, during surveillance of AIVs in live poultry markets in 2016 and 2017. Phylogenetic analysis indicated that Zhejiang H10 strains received gene segments from H10, H3, and H7 viruses from birds in East Asia. Animal inoculation tests showed that these isolates have low pathogenicity in mice and can replicate in this species. Our findings suggest these H10 AIVs have the ability to adapt to chicken or other poultry, and highlight the need of long-term surveillance.

T160A mutation-induced deglycosylation at site 158 in hemagglutinin is a critical determinant of the dual receptor binding properties of clade 2.3.4.4 H5NX subtype avian influenza viruses

Most clade 2.3.4.4 H5NX subtype avian influenza viruses possess a T160A amino acid substitution in the hemagglutinin (HA) protein that has been shown to affect the receptor binding properties of a clade 2.3.4 H5N1 virus. However, the effect of this single site mutation on the HA backbone of clade 2.3.4.4 H5NX viruses remains unclear. In this study, two H5N6 field isolates possessing HA-160A with dual α-2,3 and α-2,6 receptor binding properties (Y6 virus) and HA-160T with α-2,3 receptor binding affinity (HX virus), respectively, were selected to generate HA mutants containing all of the internal genes from A/PR8/H1N1 virus for comparative investigation. We found that the Y6-P-160A and RHX-P-160A viruses each with 160A in the HA resulting in loss of glycosylation at site 158 exhibited binding to the two receptor types, whereas the RY6-P-160T and HX-P-160T viruses each with 160T in the HA displayed selective binding to α-2,3 receptors only. In addition, differences were noted in the replication of these four H5N6 recombinants in avian and mammalian cells, as well as in their pathogenicity in mice. The contribution of deglycosylation at site 158 to the acquisition of human-like receptors was further verified in H5N2, H5N5 and H5N8 reassortants. Therefore, we conclude that the lack of glycosylation at site 158 induced by the T160A mutation in HA is a critical determinant for the dual receptor binding properties of clade 2.3.4.4 H5NX viruses. This new insight may be helpful in assessing the pandemic potential of novel H5 isolates.

ZIKV infection regulates inflammasomes pathway for replication in monocytes

ZIKV causes microcephaly by crossing the placental barrier, however, the mechanism of trans-placental dissemination of ZIKV remains unknown. Here, we sought to determine whether monocytes, which can cross tissue barriers, assist ZIKV dissemination to the fetus. We determined this by infecting monocytes with two strains of ZIKV: South American (PRVABC59) and Nigerian (IBH30656) and analyzing viral replication. We found that ZIKV infects and replicates in monocytes and macrophages, which results in the modulation of a large number of cellular genes. Analysis of these genes identified multiple pathways including inflammasome to be targeted by ZIKV, which was confirmed by analyzing the transcript levels of the proteins of inflammasome pathways, NLRP3, ASC, caspase 1, IL-1 and IL-18. Interestingly, IFNα and the IFN inducible gene, MxA were not enhanced, suggesting prevention of innate antiviral defense by ZIKV. Also, inhibition of inflammasome led to an increased transcriptional activity of IFNα, MxA and CXCL10. Based on these results we suggest that ZIKV transcription is regulated by inflammasomes.

Epidemiology, Evolution, and Pathogenesis of H7N9 Influenza Viruses in Five Epidemic Waves since 2013 in China

H7N9 influenza viruses were first isolated in 2013 and continue to cause human infections. H7N9 infections represent an ongoing public health threat that has resulted in 1344 cases with 511 deaths as of April 9, 2017. This highlights the continued threat posed by the current poultry trade and live poultry market system in China. Until now, there have been five H7N9 influenza epidemic waves in China; however, the steep increase in the number of humans infected with H7N9 viruses observed in the fifth wave, beginning in October 2016, the spread into western provinces, and the emergence of highly pathogenic (HP) H7N9 influenza outbreaks in chickens and infection in humans have caused domestic and international concern. In this review, we summarize and compare the different waves of H7N9 regarding their epidemiology, pathogenesis, evolution, and characteristic features, and speculate on factors behind the recent increase in the number of human cases and sudden outbreaks in chickens. The continuous evolution of the virus poses a long-term threat to public health and the poultry industry, and thus it is imperative to strengthen prevention and control strategies.

Molecular characterization of H6 subtype influenza viruses in southern China from 2009 to 2011

H6 avian influenza viruses (AIVs), which are prevalent in domestic and wild birds in Eurasian countries, have been isolated from pigs, a dog and a human. Routine virological surveillance at live poultry markets or poultry farms was conducted in southern China from 2009 to 2011. This study investigated the genetic and antigenic characteristics, analyzed the receptor-binding properties and evaluated the kinetics of infectivity of the AIVs in A549, MDCK and PK15 cells. A total of 14 H6N6 and 2 H6N2 isolates were obtained from four provinces in southern China. Genetic analysis indicated two distinct hemagglutinin lineages of the H6 strains cocirculating in southern China, and these strains facilitated active evolution and reassortment among multiple influenza virus subtypes from different avian species in nature. None of these isolates grouped with the novel Taiwan H6N1 virus responsible for human infection. Receptor-binding specificity assays showed that five H6 AIVs may have acquired the ability to recognize human receptors. Growth kinetics experiments showed that EV/HB-JZ/02/10(H6N2) and EV/JX/15/10(H6N6) initially reproduced faster and achieved higher titers than other viruses, suggesting that enhanced binding to α-2,6-linked sialic acids correlated with increased viral replication in mammalian cells. Overall, the results emphasize the need for continued surveillance of H6 outbreaks and extensive characterization of H6 isolates to better understand genetic changes and their implications.

Adaptive mutations in PB2 gene contribute to the high virulence of a natural reassortant H5N2 avian influenza virus in mice

The highly pathogenic A/chicken/Hebei/1102/2010 (HB10) H5N2 virus is a natural reassortant derived from circulating H5N1 and endemic H9N2 avian influenza viruses (AIV). To evaluate the potential of its interspecies transmission, we previously serially passaged the non-virulent HB10 virus in the mouse lung and obtained a high virulence variant (HB10-MA). Genomic sequencing revealed five mutations (HA-S227N, PB2-Q591K, PB2-D701N, PA-I554V and NP-R351K) that distinguished HB10-MA virus from its parental HB10 virus. In this study, we further investigated the molecular basis for the enhanced virulence of HB10-MA in mice. By generating a series of reassortants between the two viruses and evaluating their virulence in mice, we found that both PB2 and PA genes contribute to the high virulence of HB10-MA in mice, whereas PB2 gene carrying the 591K and/or 701N had a dominant function. In addition, the two amino acids showed a cumulative effect on the virulence, virus replication, and polymerase activity of HB10 or HB10-MA. Therefore, our results collectively emphasized the crucial role of PB2 gene, particularly the paired mutations of Q591K and D701N in the host adaptation of the novel reassortant H5N2 AIV in mammals, which may provide helpful insights into the pathogenic potential of emerging AIV in human beings.

Comparison of biological characteristics of H9N2 avian influenza viruses isolated from different hosts

The pathogenicity and transmissibility of H9N2 influenza viruses has been widely investigated; however, few studies comparing the biological characteristics of H9N2 viruses isolated from different hosts have been performed. In this study, eight H9N2 viruses, isolated from chickens (Ck/F98, Ck/AH and Ck/TX), pigeons (Pg/XZ), quail/(Ql/A39), ducks (Dk/Y33) and swine (Sw/YZ and Sw/TZ) were selected, and their biological characteristics were determined. The results showed that all H9N2 viruses maintained a preference for both the avian- and human-type receptors, except for Sw/TZ, which had exclusive preference for the human-type receptor. The viruses replicated well in DF-1 and MDCK cells, whereas only three isolates, Ck/F98, Ck/TX and Sw/TZ, could replicate in A549 cells and also replicated in mouse lungs, resulting in body weight loss in mice. All H9N2 viruses were nonpathogenic to chickens and were detected in the trachea and lung tissues. The viruses were shed primarily by the oropharynx and were transmitted efficiently to naïve contact chickens. Our findings suggest that all H9N2 viruses from different hosts exhibit efficient replication and contact-transmission among chickens, and chickens serve as a good reservoir for the persistence and interspecies transmission of H9N2 influenza viruses.

Novel reassortant H5N5 viruses bind to a human-type receptor as a factor in pandemic risk

Highly pathogenic avian influenza A(HPAI) H5N1 viruses pose a serious pandemic threat due to their virulence and high mortality in humans, and their increasingly expanding host range and significant ongoing evolution could enhance their human-to-human transmissibility. Recently, various reassortant viruses were detected in different domestic poultry, with the HA gene derived from the A/goose/Guangdong/1/96-like (Gs/GD-like) lineage and the NA gene from influenza viruses of other subtypes. It is reported that some natural reassortant H5N5 highly pathogenic avian influenza viruses were isolated from poultry in China. And their HA genes were belonged to a new clade 2.3.4.4. We evaluated the receptor binding property and transmissibility in guinea pigs of these reassortant H5N5 HPAIVs. The results showed that these viruses bound to both avian-type (α-2,3) and human-type (α-2,6) receptors. In addition, we found that one of these viruses, 031, not only replicated but also transmitted efficiently in guinea pigs. Therefore, such reassortant influenza viruses may pose a pandemic threat.

Hemagglutinin glycosylation modulates the pathogenicity and antigenicity of the H5N1 avian influenza virus

The location and number of glycosylation in HA proteins exhibit large variations among H5 subtype avian influenza viruses (AIVs). To investigate the effect of glycosylation in the globular head of HA on the pathogenicity and antigenicity of H5N1 AIVs, seven rescued AIVs differing in their glycosylation patterns (144N, 158N and 169N) within the HA globular head of A/Mallard/Huadong/S/2005 were generated using site directed mutagenesis. Results showed that loss of glycosylation 158N was the prerequisite for H5 AIV binding to the α2,6-linked receptor. Only in conjunction with the removal of the 158N glycosylation, the H5 AIVs harboring both 144N and 169N glycosylations obtained an optimal binding preference to the α2,6-linked receptor. Compared with the wild-type virus, growth of viruses lacking glycosylation at either 158N or 169N was significantly reduced both in MDCK and A549 cells, while replication of viruses with additional glycosylation 144N was significantly promoted. Mutant viruses with loss of 158N or 169N glycosylation sites showed increased pathogenicity, systemic spread and pulmonary inflammation in mice compared to the wild-type H5N1 virus. In addition, chicken studies demonstrated that inactivated de-glycosylation 169N mutant induced cross-reaction HI and neutralization antibody against various clades of H5N1 AIVs. Moreover, this type of glycan pattern vaccine virus provided better cross-protection in chickens compared to wild-type vaccine virus. Thus, the glycosylation alteration of HA should be considered in the global surveillance and vaccine design of H5 subtype AIVs.

Novel H5 clade 2.3.4.6 viruses with both α-2,3 and α-2,6 receptor binding properties may pose a pandemic threat

The emerging H5 clade 2.3.4.6 viruses of different NA subtypes have been detected in different domestic poultry in China. We evaluated the receptor binding property and transmissibility of four novel H5 clade 2.3.4.6 subtype highly pathogenic avian influenza viruses. The results show that these viruses bound to both avian-type (α-2,3) and human-type (α-2,6) receptors. Furthermore, we found that one of these viruses, GS/EC/1112/11, not only replicated but also transmitted efficiently in guinea pigs. Therefore, such novel H5 subtype viruses have the potential of a pandemic threat.

Two amino acid substitutions in the haemagglutinin of the 2009 pandemic H1N1 virus decrease direct-contact transmission in guinea pigs

The 2009 pandemic H1N1 influenza A virus spread across the globe and caused the first influenza pandemic of the 21st century. Many of the molecular factors that contributed to the airborne transmission of this pandemic virus have been determined; however, the direct-contact transmission of this virus remains poorly understood. In this study, we report that a combination of two mutations (N159D and Q226R) in the haemagglutinin (HA) protein of the representative 2009 H1N1 influenza virus A/California/04/2009 (CA04) caused a switch in receptor binding preference from the α2,6-sialoglycan to the α2,3-sialoglycan receptor, and decreased the binding intensities for both glycans. In conjunction with a significantly decreased replication efficiency in the nasal epithelium, this limited human receptor binding affinity resulted in inefficient direct-contact transmission of CA04 between guinea pigs. Our findings highlight the role of the HA gene in the transmission of the influenza virus.

Isolation and characterization of two H5N1 influenza viruses from swine in Jiangsu Province of China

Pigs are susceptible to infection with both human and avian influenza A viruses and are considered intermediate hosts that facilitate virus reassortment. Although H5N1 virus has spread to a wide range of avian and mammalian species, data about swine H5N1 isolates are scarce. To determine whether Asian H5N1 influenza viruses had been transmitted to pigs, a total of 1,107 nasal swab samples from healthy swine were collected from 2008 to 2009 in Jiangsu province of eastern China. In this survey, two H5N1 viruses A/swine/Jiangsu/1/2008 (JS/08) and A/swine/Jiangsu/2/2009 (JS/09) were isolated and identified. Phylogenetic analysis showed that JS/08 and JS/09 belonged to clade 7 and clade 2.3.4, respectively, and shared over 99.0 % sequence identity with poultry H5N1 isolates of the same clade in China. Receptor specificity analysis also showed that both of the swine H5N1 isolates bound preferentially to avian-type receptors. However, experiments in mammals indicated that JS/09 was moderately pathogenic to mice without prior adaption, whereas JS/08 had limited ability to replicate. Our findings suggest that pigs are naturally infected with avian H5N1 virus and highlight the potential threat to public health due to adaption or reassortment of H5N1 virus in this species.

Modular glycosphere assays for high-throughput functional characterization of influenza viruses

Background

The ongoing global efforts to control influenza epidemics and pandemics require high-throughput technologies to detect, quantify, and functionally characterize viral isolates. The 2009 influenza pandemic as well as the recent in-vitro selection of highly transmissible H5N1 variants have only increased existing concerns about emerging influenza strains with significantly enhanced human-to-human transmissibility. High-affinity binding of the virus hemagglutinin to human receptor glycans is a highly sensitive and stringent indicator of host adaptation and virus transmissibility. The surveillance of receptor-binding characteristics can therefore provide a strong additional indicator for the relative hazard imposed by circulating and newly emerging influenza strains.

Results

Streptavidin-coated microspheres were coated with selected biotinylated glycans to mimic either human or avian influenza host-cell receptors. Such glycospheres were used to selectively capture influenza virus of diverse subtypes from a variety of samples. Bound virus was then detected by fluorescently labelled antibodies and analyzed by quantitative flow cytometry. Recombinant hemagglutinin, inactivated virus, and influenza virions were captured and analyzed with regards to receptor specificity over a wide range of analyte concentration. High-throughput analyses of influenza virus produced dose–response curves that allow for functional assessment of relative receptor affinity and thus transmissibility.

Conclusions

Modular glycosphere assays for high-throughput functional characterization of influenza viruses introduce an important tool to augment the surveillance of clinical and veterinarian influenza isolates with regards to receptor specificity, host adaptation, and virus transmissibility.

Chinese and global distribution of H9 subtype avian influenza viruses

H9 subtype avian influenza viruses (AIVs) are of significance in poultry and public health, but epidemiological studies about the viruses are scarce. In this study, phylogenetic relationships of the viruses were analyzed based on 1233 previously reported sequences and 745 novel sequences of the viral hemagglutinin gene. The novel sequences were obtained through large-scale surveys conducted in 2008-2011 in China. The results revealed distinct distributions of H9 subtype AIVs in different hosts, sites and regions in China and in the world: (1) the dominant lineage of H9 subtype AIVs in China in recent years is lineage h9.4.2.5 represented by A/chicken/Guangxi/55/2005; (2) the newly emerging lineage h9.4.2.6, represented by A/chicken/Guangdong/FZH/2011, has also become prevalent in China; (3) lineages h9.3.3, h9.4.1 and h9.4.2, represented by A/duck/Hokkaido/26/99, A/quail/Hong Kong/G1/97 and A/chicken/Hong Kong/G9/97, respectively, have become globally dominant in recent years; (4) lineages h9.4.1 and h9.4.2 are likely of more risk to public health than others; (5) different lineages have different transmission features and host tropisms. This study also provided novel experimental data which indicated that the Leu-234 (H9 numbering) motif in the viral hemagglutinin gene is an important but not unique determinant in receptor-binding preference. This report provides a detailed and updated panoramic view of the epidemiological distributions of H9 subtype AIVs globally and in China, and sheds new insights for the prevention of infection in poultry and preparedness for a potential pandemic caused by the viruses.

Receptor binding surveillance of influenza clinical isolates

Aims: The outbreak of highly pathogenic avian influenza H5N1 in poultry and the influenza A pandemic have wreaked havoc on public health. Viruses alter their carbohydrate binding preferences, thereby causing pandemics all over the world. In this study, we tried to investigate the carbohydrate binding specificity of influenza clinical isolates. Materials & methods: Biotin-conjugated polyacrylamide-based glycan epitopes were immobilized on UltraBind™ membranes and used to survey the glycan-binding preference of influenza clinical isolates, including seasonal influenza A, A(H1N1)pdm09 and influenza B viruses. In addition, the DNA sequences of influenza B virus hemagglutinin were analyzed. Results: Human influenza A, especially the A(H1N1)pdm09 viruses, accepted α2,6 and α2,3 sialylated glycans, sulfated glycans and α2,8 sialosides. Although all influenza B clinical isolates bound strongly to NeuAc, 6´-sialyl lactose and sialyl biantennary N-glycan, some viruses also recognized sulfated and α2,3 sialylated glycans. According to the nucleotide sequences of viral hemagglutinin, influenza B viruses that exhibited weak interaction with sulfated and α2,3 sialylated glycans showed fewer charged amino acids. Conclusion: The substrate specificities of influenza clinical isolates were surveyed. Influenza A exhibited more complicated glycan-binding patterns than influenza B viruses. Our findings provided a systematic investigation of receptor-binding specificities for influenza clinical isolates, as well as useful information for exploring viral tropism.

Profiling of influenza viruses by high-throughput carbohydrate membrane array

BACKGROUND

Carbohydrate-protein interactions participate in many biological functions. To characterize the binding interactions represents a longstanding challenge.

METHOD

We developed a glycan membrane array to study the interactions of carbohydrates with lectins, proteins and viruses, including 17 lectins, four antibodies (that are specific to different Lewis antigens), one recombinant H5N1 hemagglutinin, and five influenza B clinical isolates.

RESULTS

The results were found to be comparable to previous reports, indicating the efficacy and reliability of our developed method.

CONCLUSION

This carbohydrate membrane array represents a convenient, reliable and low-cost method to examine the carbohydrate-binding features of various proteins, high-throughput drug screening and the glycan-binding surveillance of influenza viruses.

A FRET based melting curve analysis to detect nucleotide variations in HA receptor-binding site of H5N1 virus

Outbreaks of highly pathogenic H5N1 influenza A virus represent a major public health problem because of the possibility of direct transmission of these viruses from avian species to humans. For influenza H5N1 hemagglutinin, a switch from SA-a-2, 3-Gal to SA-a-2, 6-Gal receptor specificity is a critical step that could lead to inter-human transmission. The monitoring of the receptor-binding preference of H5N1 viruses represents an instrument to detect a potential pandemic virus. The aim of this study was to develop a method based on the fluorescence resonance energy transfer (FRET) technology and melting peaks analysis for rapid screening of pandemic H5N1 influenza A virus. Three selected probes corresponding to a 23bp nucleotide sequence of the avian receptor-binding site were used in a real-time RT-PCR to detect nucleotide variations. Five strains of avian influenza A viruses isolated from avian species and two synthesized HA gene were tested. The results showed that the melting peaks analysis is a reliable screening method for detecting the variability of the H5N1 receptor-binding site.

Prediction of avian influenza A binding preference to human receptor using conformational analysis of receptor bound to hemagglutinin

BACKGROUND

It is known that the highly pathogenic avian influenza A virus H5N1 binds strongly and with high specificity to the avian-type receptor by its hemagglutinin surface protein. This specificity is normally a barrier to viral transmission from birds to humans. However, strains may emerge with mutated hemagglutinin, potentially changing the receptor binding preference from avian to human-type. This hypothesis has been proven correct, since viral isolates from Vietnam and Thailand have been found which have increased selectivity toward the human cell receptor. The change in binding preference is due to mutation, which can be computationally modelled. The aim of this study is to further explore whether computational simulation could be used as a prediction tool for host type selectivity in emerging variants.

RESULTS

Molecular dynamics simulation was employed to study the interactions between receptor models and hemagglutinin proteins from H5N1 strains A/Duck/Singapore/3/97, mutated A/Duck/Singapore/3/97 (Q222L, G224S, Q222L/G224S), A/Thailand/1(KAN-1)/2004, and mutated A/Thailand/1(KAN-1)/2004 (L129V/A134V). The avian receptor was represented by Sia alpha(2,3)Gal substructure and human receptor by Sia alpha(2,6)Gal. The glycoside binding conformation was monitored throughout the simulations since high selectivity toward a particular host occurs when the sialoside bound with the near-optimized conformation.

CONCLUSION

The simulation results showed all hemagglutinin proteins used the same set of amino acid residues to bind with the glycoside; however, some mutations alter linkage preferences. Preference toward human-type receptors is associated with a positive torsion angle, while avian-type receptor preference is associated with a negative torsion angle. According to the conformation analysis of the bound receptors, we could predict the relative selectivity in accordance with in vitro experimental data when disaccharides receptor analogs were used.