An analysis on HA, NA gene/protein evolution and the variability of antigenicity sites of influenza A (H7N9) virus

Abstract

To explore the hemagglutinin (HA), neuraminidase (NA) gene/protein evolution and the variability of antigenicity sites of influenza A (H7N9) virus. The sequences of HA, NA gene and amino acid (AA) were downloaded from National Center for Biotechnology Information (NCBI) and the Global Initiative on Sharing All Influenza Data (GISAID) database. The bioinformatic software programs of Clustal-W, MEGA 5.0, NetNGlyc 1.0 Server and DNAMAN were employed to analyze the variations and predict the possible antigenicity sites. A total of 26 HA gene and AA and 24 NA gene and AA sequences were analyzed. HA, NA gene and AA sequence of H7N9 virus were conservative in America but not in Eurasian area. The HA and NA gene evolutions could be divided into 2 general systems: Eurasian and America. Only one basic AA R (Arg) was close to HA cleavage sites of H7N9 virus. Regional differences existed between HA protein cleavage and NA protein glycosylation sites. And the HA glycosylation sites were conservative. Several antigenicity sites of HA and NA protein changed in Eurasian area and America. In 7 cases, novel H7N9 evolved virus isolated from China were one branch of Eurasian area. Five AAs were deleted in stalk region of NA residues 69 to 73. HA protein cleavage and glycosylation sites did not carry the variant. However, several antigenicity sites of HA and NA protein changed compared with other virus strains. Regional differences exist in HA and NA gene evolution of H7N9 virus. The deletion of 5 AAs in stalk and the variation of several antigenicity sites of HA and NA protein may lead to an outbreak of H7N9 virus in humans.