Insights into avian influenza virus pathogenicity: the hemagglutinin precursor HA0 of subtype H16 has an alpha-helix structure in its cleavage site with inefficient HA1/HA2 cleavage. 2012

Xishan Lu, and Yi Shi, and Feng Gao, and Haixia Xiao, and Ming Wang, and Jianxun Qi, and George F Gao
College of Veterinary Medicine, China Agricultural University, Beijing, China.

With a new serotype (H17) of hemagglutinin (HA) recently being discovered, there are now 17 serotypes (H1 to H17) of influenza A viruses in total. It is believed that HA is initially expressed as a precursor of HA0 and then cleaved into HA1 and HA2, forming a disulfide bond-linked complex, for its full function. Structural data show that a loop structure exists in the cleavage site between HA1 and HA2, and this flexible loop is crucial for the efficient cleavage of HA0. Here, the crystal structures of H16 (a low-pathogenicity avian influenza virus) in their HA0 form (H16HA0) have been solved at 1.7-Å and 2.0-Å resolutions. To our surprise, an α-helix element in the cleavage site which inserts into the negatively charged cavity with the key residue R329 hidden behind the helix was observed. In vitro trypsin cleavage experiments demonstrated inefficient cleavage of H16HA0 under both neutral and low-pH conditions. The results provide new insights into influenza A virus pathogenicity; both the relatively stable α-helix structure in the flexible cleavage loop and inaccessibility of the cleavage site likely contribute to the low pathogenicity of avian influenza A virus. Furthermore, compared to all of the HAs whose structures have been solved, H16 is a good reference for assigning the HA subtypes into two groups on the basis of the three-dimensional structure, which is consistent with the phylogenetic grouping. We conclude that in light of the current H16HA0 structure, the natural α-helix element might provide a new opportunity for influenza virus inhibitor design.

UI MeSH Term Description Entries
D008958 Models, Molecular Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures. Molecular Models,Model, Molecular,Molecular Model
D008969 Molecular Sequence Data Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories. Sequence Data, Molecular,Molecular Sequencing Data,Data, Molecular Sequence,Data, Molecular Sequencing,Sequencing Data, Molecular
D009036 Moths Insects of the suborder Heterocera of the order LEPIDOPTERA. Antheraea,Giant Silkmoths,Giant Silkworms,Silkmoths, Giant,Silkworms, Giant,Antheraeas,Giant Silkmoth,Giant Silkworm,Moth,Silkmoth, Giant,Silkworm, Giant
D009980 Influenza A virus The type species of the genus ALPHAINFLUENZAVIRUS that causes influenza and other diseases in humans and animals. Antigenic variation occurs frequently between strains, allowing classification into subtypes and variants. Transmission is usually by aerosol (human and most non-aquatic hosts) or waterborne (ducks). Infected birds shed the virus in their saliva, nasal secretions, and feces. Alphainfluenzavirus influenzae,Avian Orthomyxovirus Type A,FLUAV,Fowl Plague Virus,Human Influenza A Virus,Influenza Virus Type A,Influenza Viruses Type A,Myxovirus influenzae-A hominis,Myxovirus influenzae-A suis,Myxovirus pestis galli,Orthomyxovirus Type A,Orthomyxovirus Type A, Avian,Orthomyxovirus Type A, Human,Orthomyxovirus Type A, Porcine,Pestis galli Myxovirus,Fowl Plague Viruses,Influenza A viruses,Myxovirus influenzae A hominis,Myxovirus influenzae A suis,Myxovirus, Pestis galli,Myxoviruses, Pestis galli,Pestis galli Myxoviruses,Plague Virus, Fowl,Virus, Fowl Plague
D002460 Cell Line Established cell cultures that have the potential to propagate indefinitely. Cell Lines,Line, Cell,Lines, Cell
D003001 Cloning, Molecular The insertion of recombinant DNA molecules from prokaryotic and/or eukaryotic sources into a replicating vehicle, such as a plasmid or virus vector, and the introduction of the resultant hybrid molecules into recipient cells without altering the viability of those cells. Molecular Cloning
D003460 Crystallization The formation of crystalline substances from solutions or melts. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed) Crystalline Polymorphs,Polymorphism, Crystallization,Crystal Growth,Polymorphic Crystals,Crystal, Polymorphic,Crystalline Polymorph,Crystallization Polymorphism,Crystallization Polymorphisms,Crystals, Polymorphic,Growth, Crystal,Polymorph, Crystalline,Polymorphic Crystal,Polymorphisms, Crystallization,Polymorphs, Crystalline
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D006863 Hydrogen-Ion Concentration The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH pH,Concentration, Hydrogen-Ion,Concentrations, Hydrogen-Ion,Hydrogen Ion Concentration,Hydrogen-Ion Concentrations
D000595 Amino Acid Sequence The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION. Protein Structure, Primary,Amino Acid Sequences,Sequence, Amino Acid,Sequences, Amino Acid,Primary Protein Structure,Primary Protein Structures,Protein Structures, Primary,Structure, Primary Protein,Structures, Primary Protein

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