Avian influenza A (H9N2): computational molecular analysis and phylogenetic characterization of viral surface proteins isolated between 1997 and 2009 from the human population

Azeem M Butt,Samerene Siddique,Yigang Tong,Muhammad Idrees

doi:10.1186/1743-422x-7-319

Abstract

BackgroundH9N2 avian influenza A viruses have become panzootic in Eurasia over the last decade and have caused several human infections in Asia since 1998. To study their evolution and zoonotic potential, we conducted an in silico analysis of H9N2 viruses that have infected humans between 1997 and 2009 and identified potential novel reassortments.ResultsA total of 22 hemagglutinin (HA) and neuraminidase (NA) nucleotide and deduced amino acid sequences were retrieved from the NCBI flu database. It was identified that mature peptide sequences of HA genes isolated from humans in 2009 had glutamine at position 226 (H3) of the receptor binding site, indicating a preference to bind to the human α (2-6) sialic acid receptors, which is different from previously isolated viruses and studies where the presence of leucine at the same position contributes to preference for human receptors and presence of glutamine towards avian receptors. Similarly, strains isolated in 2009 possessed new motif R-S-N-R in spite of typical R-S-S-R at the cleavage site of HA, which isn't reported before for H9N2 cases in humans. Other changes involved loss, addition, and variations in potential glycosylation sites as well as in predicted epitopes. The results of phylogenetic analysis indicated that HA and NA gene segments of H9N2 including those from current and proposed vaccine strains belong to two different Eurasian phylogenetic lineages confirming possible genetic reassortments.ConclusionsThese findings support the continuous evolution of avian H9N2 viruses towards human as host and are in favor of effective surveillance and better characterization studies to address this issue.

Highlights

H9N2 avian influenza A viruses have become panzootic in Eurasia over the last decade and have caused several human infections in Asia since 1998
Bioinformatics analysis of HA and NA from H9N2 viruses was performed and the key residues in receptor binding sites (RBS), the cleavage motifs of HA and NA hemadsorbing sites (HB), stalk length and enzyme active sites were studied in detail
The presence of glutamine (Q) at position 234 (H3 numbering: 226) is a typical avian virus signature, and it has been reported that presence of this amino acid results in a preference for binding to 2,3-linked sialic acid whereas, in the case of leucine (L) at the same position, there is a preference for 2,6-linked sialic acid and potential cause of reported human infections [5,6,23,24,25]

Summary

Introduction

H9N2 avian influenza A viruses have become panzootic in Eurasia over the last decade and have caused several human infections in Asia since 1998. Influenza viruses belonging to the Orthomyxoviradae family of viruses are divided into eight single stranded RNA segments encoding ten proteins These include two surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA), along with nucleoproteins (NP), three polymerase proteins (PA, PB1, PB2) two matrix proteins (M1, M2) and non-structural proteins (NS1, NS2) [8,9,10,11]. Virus aggregation is prevented by the NA glycoprotein and by the cleavage of the a-ketosodic linkage between sialic acid and an adjacent sugar residue This facilitates the movement of the virus to and from the site of infection by destruction of receptors recognized by HA [12]. The Eurasian lineage can be further divided into three major sublineages; the G1 lineage, represented by A/Quail/Hong Kong/G1/97 (G1-like); the Y280 lineage, represented by three prototype viruses A/duck/Hong Kong/Y280/97 (Y280-like), A/Chicken/ Beijing/1/94 (BJ94-like), and A/Chicken/Hong Kong/G9/ 97 (G9-like) and the Korean lineage, represented by A/chicken/Korea/38349-p96323/96 (Korean-like) and A/duck/Hong Kong/Y439/97 (Y439-like) [7,13,14]

Objectives

Methods

Results

Conclusion