As part of our ongoing influenza surveillance program in South China, 19 field strains of H9N2 subtype avian influenza viruses (AIVs) were isolated from dead or diseased chicken flocks in Guangdong province, South China, between 2012 and 2013. Hemagglutinin (HA) genes of these strains were sequenced and analyzed and phylogenic analysis showed that 12 of the 19 isolates belonged to the lineage h9.4.2.5, while the other seven belonged to h9.4.2.6. Specifically, we found that all of the viruses isolated in 2013 belonged to lineage h9.4.2.5. The lineage h9.4.2.5 viruses contained a PSRSSRdownward arrowGLF motif at HA cleavage site, while the lineage h9.4.2.6 viruses contained a PARSSRdownward arrowGLF at the same position. Most of the isolates in lineage h9.4.2.5 lost one potential glycosylation site at residues 200-202, and had an additional one at residues 295-297 in HA1. Notably, 19 isolates had an amino acid exchange (Q226L) in the receptor binding site, which indicated that the viruses had potential affinity of binding to human like receptor. The present study shows the importance of continuing surveillance of new H9N2 strains to better prepare for the next epidemic or pandemic outbreak of H9N2 AIV infections in chicken flocks.
Animals ; *Chickens ; China ; Hemagglutinin Glycoproteins, Influenza Virus/chemistry/*genetics/metabolism ; Influenza A Virus, H9N2 Subtype/*genetics/metabolism ; Influenza in Birds/virology ; Phylogeny ; Poultry Diseases/*virology ; Sequence Analysis, RNA/veterinary

Since March 2009, pandemic A/H1N1/2009 influenza virus has been spreading throughout many countries including China. The emerged virus caused great harm to human health and social economy. Hemagglutinin (HA) is the most important viral surface glycoprotein, mainly possessing three kinds of functions: (1) binding to host cell receptor, (2) triggering the fusion between viral envelop and target cell membrane, (3) stimulating the body to generate the neutralizing antibody. Advances in the structure, primary function, evolution and antigenicity of pandemic A/H1N1/2009 influenza virus HA protein are reviewed in this paper.
Animals ; Evolution, Molecular ; Hemagglutinin Glycoproteins, Influenza Virus ; chemistry ; genetics ; immunology ; metabolism ; Humans ; Influenza A Virus, H1N1 Subtype ; genetics ; immunology ; pathogenicity ; physiology ; Influenza, Human ; epidemiology ; virology ; Pandemics

The distribution of glycosylation sites in HA proteins was various among H5 subtype avian influenza viruses (AIVs), however, the role of glycosylation sites to the virus is still unclear. In this study, avian influenza H5N1 viruses with deletion of the glycosylation sites in HA were constructed and rescued by site direct mutation and reverse genetic method, and their biological characteristics and virulence were determined. The result showed that the mutants were confirmed to be corrected by HA gene sequencing and Western blot analysis. The EID50 and TCID50 tested in SPF chick embryo and MDCK cells of a mutant rSdelta158 with deletion of glycosylation site at position 158 were slight lower than that of wild type rescued virus rS, and the plaque diameter of rSdelta158 was significant smaller than that of rS. The EID50 and TCID50 of mutants rSdelta169 and rSdelta290 with deletion of glycosylation sites at position 169 and 290, respectively, were slight higher than that of wild type rescued virus rS, the plaque diameters of rSdelta169 and rSdelta290 were similar as that of rS, but the plaque numbers of rSdelta169 and rSdelta290 were 10-fold higher than that to rS. On the other hand, the rSdelta158, rSdelta169 and rSdelta290 showed similar growth rate in chicken embryo fibroblast as rS. All viruses remained high pathogenicity to SPF chickens. Therefore, the growth of AIV can be affected by changes of glycosylation sites in HA protein, by which the effect is variable in different cells.
Amino Acid Motifs ; Animals ; Cell Line ; Chick Embryo ; Chickens ; Glycosylation ; Hemagglutinin Glycoproteins, Influenza Virus ; chemistry ; genetics ; metabolism ; Influenza A Virus, H5N1 Subtype ; chemistry ; genetics ; growth & development ; metabolism ; Influenza in Birds ; virology ; Poultry Diseases ; virology

The purpose of this study is to explore the effects of the HA sequence variation on the pathogenicity and antigenicity of avian influenza virus(AIV). Haemagglutinin (HA) genes from, 6 of 25 avian influenza viruses (AIVs) H9N2 strains with different pathogenicity isolated in central China during last 10 years were amplified by reverse transcriptase PCR (RT-PCR), completely sequenced and phylogenetically analyzed. The purpose of this study was to explore the effects of the HA sequence variation on the pathogenicity and antigenicity of AIV. The results showed that all 6 representative H9N2 isolates belong to low pathogenic AIVs, since none of the amino acid sequences at the cleavage site of the HA of the isolates possessed the basic motif required for highly pathogenic viruses (R-X-R/K-R). There were eight potential glycosylation sites in HA of the isolates, except that 3# and 12# had an extra one. The higher pathogenicity of 3# and 12# was probably due to the extra glycosylation site (145aa-147aa) in HA1, which might alter the conformational structure of HA resulting in the mutation or deletion of the binding sites of anti-HA antibody, and has effects on receptor binding sites thus changed the antigenicity of the virus. Our results suggested that attention should be paid to the transmission and natural evolution of H9N2 AIV in order to control AIV H9N2.
Animals ; Chickens ; China ; Computational Biology ; Glycosylation ; Hemagglutinin Glycoproteins, Influenza Virus ; chemistry ; genetics ; immunology ; metabolism ; Influenza A Virus, H9N2 Subtype ; classification ; genetics ; immunology ; isolation & purification ; Phylogeny ; Reverse Transcriptase Polymerase Chain Reaction ; Sequence Alignment ; Sequence Analysis, DNA

To understand the HA1 genetic variation characterization of influenza H3N2 virus isolates in Zhu-hai during 2008-2009, we selected 20 of H3N2 Influenza strains cultured in MDCK cell. Viral RNAs were extracted and amplified by using RT-PCR. The amplified products were purified after identified by gel electrophoresis and then the nucleotide sequences of the amplicons were determined. The results were analyzed by the software ClustalX and MEGA4. 1. When compared with the amino acid sequences of the epitopes of HA1 district of H3N2 influenza vaccine recommended by WHO in 2008, changes were found in those of H3N2 influenza strains in Zhuhai in 2008: K140I in all of H3N2 influenza strains, L157S in 08-0343 and 08-0677, K158R in 08-0466, 08-0620 and 08-0667, K173E in 08-0466 and 08-0620, K173N in 08-0667, and I192T in 08-0667. The epitopes of HA1 district of H3N2 influenza strains in Zhuhai in 2009 are different from that of H3N2 influenza vaccine during the same time: K173Q and P194L occur in all of H3N2 influenza strains, N144K, K158N, and N189K occur in the strains except the strain 09-0056. HA1 domain of H3N2 influenza strains in 2009 has lost a glycosylation site at amino acid position 144 while the glycosylation sites of HA1 domain of H3N2 influenza stains isolated in 2008 remained. This study suggested that H3N2 influenza virus in Zhuhai in 2008 was not evolved a novel variant and H3N2 influenza variant in 2009 was attributed to antigenic drift in HA1 district.
Animals ; Antigens, Viral ; immunology ; Cell Line ; China ; Dogs ; Epitopes ; immunology ; Glycosylation ; Hemagglutinin Glycoproteins, Influenza Virus ; chemistry ; genetics ; immunology ; metabolism ; Humans ; Influenza A Virus, H3N2 Subtype ; classification ; genetics ; immunology ; isolation & purification ; Mutation ; Phylogeny ; Sequence Analysis, DNA

Avian influenza A virus continues to pose a global threat with occasional H5N1 human infections, which is emphasized by a recent severe human infection caused by avian-origin H7N9 in China. Luckily these viruses do not transmit efficiently in human populations. With a few amino acid substitutions of the hemagglutinin H5 protein in the laboratory, two H5 mutants have been shown to obtain an air-borne transmission in a mammalian ferret model. Here in this study one of the mutant H5 proteins developed by Kawaoka's group (VN1203mut) was expressed in a baculovirus system and its receptor-binding properties were assessed. We herein show that the VN1203mut had a dramatically reduced binding affinity for the avian α2,3-linkage receptor compared to wild type but showed no detectable increase in affinity for the human α2,6-linkage receptor, using Surface Plasmon Resonance techonology. Further, the crystal structures of the VN1203mut and its complexes with either human or avian receptors demonstrate that the VN1203mut binds the human receptor in the same binding manner (cis conformation) as seen for the HAs of previously reported 1957 and 1968 pandemic influenza viruses. Our receptor binding and crystallographic data shown here further confirm that the ability to bind the avian receptor has to decrease for a higher human receptor binding affinity. As the Q226L substitution is shown important for obtaining human receptor binding, we suspect that the newly emerged H7N9 binds human receptor as H7 has a Q226L substitution.
Air Microbiology ; Crystallography, X-Ray ; Glycosylation ; Hemagglutinin Glycoproteins, Influenza Virus ; chemistry ; genetics ; metabolism ; Humans ; Influenza A Virus, H5N1 Subtype ; chemistry ; metabolism ; Influenza A Virus, H7N9 Subtype ; chemistry ; Models, Molecular ; Mutant Proteins ; chemistry ; genetics ; metabolism ; Protein Binding ; Protein Stability ; Receptors, Cell Surface ; genetics ; metabolism ; Solubility ; Surface Plasmon Resonance ; Temperature

Animals ; Antiviral Agents ; pharmacology ; therapeutic use ; DNA-Directed RNA Polymerases ; antagonists & inhibitors ; Drug Discovery ; Hemagglutinin Glycoproteins, Influenza Virus ; chemistry ; metabolism ; Humans ; Influenza A virus ; drug effects ; genetics ; metabolism ; Influenza, Human ; drug therapy ; Molecular Targeted Therapy ; Neuraminidase ; antagonists & inhibitors ; RNA-Binding Proteins ; antagonists & inhibitors ; Signal Transduction ; drug effects ; Viral Core Proteins ; antagonists & inhibitors ; Viral Matrix Proteins ; antagonists & inhibitors