Avian Influenza A Viruses Differ from Human Viruses by Recognition of Sialyloligosaccharides and Gangliosides and by a Higher Conservation of the HA Receptor-Binding Site

Abstract

Avian influenza virus strains representing most hemagglutinin (HA) subtypes were compared with human influenza A (H1N1,H3N2) and B virus isolates, including those with no history of passaging in embryonated hen's eggs, for their ability to bind free N-acetylneuraminic acid (Neu5Ac) and sialylollgosaccharides in a competitive binding assay and to attach to gangliosides in a solid-phase adsorption assay. The avian viruses, irrespective of their HA subtype, showed a higher affinity for sialyl-3-lactose and the other Neu5Ac2-3Gal-terminated oligosaccharides and a lower affinity for sialyl-6-lactose than for free Neu5Ac, indicative of specific interactions between the HA and the 3-linked Gal and poor accommodation of 6-linked Gal in the avian receptor-binding site (RBS). Human H1 and H3 strains, by contrast, were unable to bind to 3-linked Gal, interacting instead with the asialic portion of sialyl-6-(N-acetyllactosamine). Different parts of this moiety were recognized by H3 and H1 subtype viruses (Gal and GlcNAc, respectively). Comparison of the HA amino acid sequences revealed that residues in positions. 138, 190, 194, 225, 226, and 228 are conserved in the avian RBS, while the human HAs harbor substitutions at these positions. A characteristic feature of avian viruses was their binding to Neu5Ac2-3Gal-containing gangliosides. This property of avian precursor viruses was preserved in early human H3 isolates, but was gradually lost with further circulation of the H3 HA in humans. Consequently, later human H3 isolates, as well as H1 and type B human strains, were unable to bind to short Neu5Ac2-3Gal-terminated gangliosides, an incompatibility that correlated with higher glycosylation of the HA globular head of human viruses. Our results suggest that the RBS is highly conserved among HA subtypes of avian influenza virus, while that of human viruses displays distinctive genotypic and phenotypic variability.

Origin and evolution of the 1918 “Spanish” influenza virus hemagglutinin gene

“…(1999) galactose by the ␣2,3 linkage (SA␣2,3Gal), whereas humanadapted HAs prefer the ␣2,6 linkage (SA␣2,6Gal). A shift from SA␣2,3Gal to SA␣2,6Gal binding seems to be a critical step in the adaptation of an avian HA to the human host (20,22,23). Determining the minimal changes allowing avian H1s to function in humans is complicated by the fact that the earliest H1 strains have been maintained in different laboratory host cells, a practice that selects for mutations in the receptor-binding sites (20).…”

“…The 1918 sequence, having been derived directly from viral RNA, is free of any possible artifacts of laboratory adaptation. A subset of amino acids that are unvaried in all avian HAs but vary in mammalian-adapted HAs has been identified (23) and constitutes the minimum receptor-binding site. Changes in these amino acids have been shown to affect receptor-binding specificity (24) and antigenicity (25).…”

Characterization of a Chicken Embryo-Adapted H9N2 Subtype Avian Influenza Virus

“…Korean field isolates are less productive in ECE, and their productivities should be improved prior to use in vaccine development [9,16,17]. The efficiency of influenza virus replication in ECE can be affected by the receptor affinity of HA, the balance of HA and NA activities, and internal genes [13,[18][19][20][21][22][23]. A good vaccine candidate should be cost-effective in production, antigenically representative of contemporary field strains, and safe for chickens and mammals.…”

Antigenic drift in the evolution of H1N1 influenza A viruses resulting from deletion of a single amino acid in the haemagglutinin gene

“…S2 Fig. S1 available in JGV Online) (Matrosovich et al, 1997(Matrosovich et al, , 2000. Interestingly, Kaverin et al.…”

“…Additional amino acid differences in the receptor-binding pocket of A/ Hebei/52/94 and A/Beijing/262/95 HAs, including residues 190, 225 and 226 (H3 numbering) known to impact receptor specificity, may play a role in magnifying the effect of deleting residue 134 in A/Hebei/52/94 HA ( Supplementary Fig. S1 available in JGV Online) (Matrosovich et al, 1997(Matrosovich et al, , 2000. Interestingly, Kaverin et al (2000) reported that virus aggregation, resulting from incompatibilities between the HA and NA glycoprotein activities, could be overcome by mutation in the vicinity of the receptor pocket of HA by increasing the local negative charge.…”