Quantitative description of glycan-receptor binding of influenza A virus H7 hemagglutinin - PubMed (original) (raw)

Quantitative description of glycan-receptor binding of influenza A virus H7 hemagglutinin

Karunya Srinivasan et al. PLoS One. 2013.

Erratum in

Abstract

In the context of recently emerged novel influenza strains through reassortment, avian influenza subtypes such as H5N1, H7N7, H7N2, H7N3 and H9N2 pose a constant threat in terms of their adaptation to the human host. Among these subtypes, it was recently demonstrated that mutations in H5 and H9 hemagglutinin (HA) in the context of lab-generated reassorted viruses conferred aerosol transmissibility in ferrets (a property shared by human adapted viruses). We previously demonstrated that the quantitative binding affinity of HA to α2→6 sialylated glycans (human receptors) is one of the important factors governing human adaptation of HA. Although the H7 subtype has infected humans causing varied clinical outcomes from mild conjunctivitis to severe respiratory illnesses, it is not clear where the HA of these subtypes stand in regard to human adaptation since its binding affinity to glycan receptors has not yet been quantified. In this study, we have quantitatively characterized the glycan receptor-binding specificity of HAs from representative strains of Eurasian (H7N7) and North American (H7N2) lineages that have caused human infection. Furthermore, we have demonstrated for the first time that two specific mutations; Gln226→Leu and Gly228→Ser in glycan receptor-binding site of H7 HA substantially increase its binding affinity to human receptor. Our findings contribute to a framework for monitoring the evolution of H7 HA to be able to adapt to human host.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1

Figure 1. Glycan receptor-binding specificity of FC, CC, NY/107 and mNY/107:A135T HA.

A, shows dose-dependent direct glycan array binding of FC HA. Specific high affinity binding to avian receptors (3′ SLN, 3′ SLNLN and 3′ SLNLNLN) and no binding to human receptors is observed. B, shows dose-dependent direct glycan array binding of CC HA. High affinity binding to avian receptors is observed. In comparison with FC, there is observable binding to human receptors (6′SLN-LN and 6′SLN) albeit at orders of magnitude lower affinity than binding to avian receptors. C, shows dose-dependent direct glycan array binding of NY/107 HA. High affinity binding to avian receptors (3′SLN-LN and 3′SLN-LN-LN) is observed with binding affinity for 3′SLN lower than that of FC and CC HAs. Binding to human receptor is observed but at much lower affinity (by orders of magnitude) than binding to avian receptors. D, shows dose-dependent direct glycan array binding of mutant mNY/107:A135T HA. Introduction of glycosylation sequon at Asn-133 does not seem to alter binding of this mutant HA in relation to the wild type.

Figure 2

Figure 2. Glycan receptor-binding specificity of Gln226→Leu/Gly228→Ser mutant of FC and CC.

A and B, respectively show dose-dependent direct glycan array binding of mFC: LS and mCC: LS mutant HAs. The double mutation leads to a substantial increase in human-receptor binding signals to a level that allowed calculation of apparent binding affinity parameter Kd'. The double mutation also lowers the avian-receptor binding affinity of mutant HAs relative to the corresponding wild-type HAs.

Figure 3

Figure 3. Structural complexes of FC – avian receptor and mFC:LS – human receptor.

A, shows the structural complex of RBS of FC HA with avian receptor derived from the X-ray co-crystal structure of this complex (PDB ID: 4DJ7). B, shows structural complex of RBS of mFC:LS HA with human receptor derived based on homology-model of mFC:LS (generated using automated mode in Swiss Model:

http://swissmodel.expasy.org/

). The coordinates of the human receptor were obtained from PDB ID: 2WR7. The mFC:LS human receptor structural complex was obtained by superimposing the HA1 domain (bound to this receptor) of 2WR7 with that of mFC:LS HA1 homology model followed by subsequent energy minimization. The critical contacts made by Gln-226 (in FC HA) and Leu-226 (in mFC:LS HA) with glycan receptor is shown using a dotted line.

Figure 4

Figure 4. Tissue binding specificity of FC and mFC:LS for human tracheal and alveolar sections.

A, Extensive staining of apical surface of human tracheal epithelia for the mFC: LS (green) against propidium iodide staining (in red) is observed. Bright staining of what appears to be goblet cells (inset at 20x magnification; indicated by white arrow) by this mutant HA resembles a similar pattern that was previously observed with 1918 H1N1 and 1958 H2N2 HAs. B, Shows minimal to no staining of apical surface of tracheal section by FC consistent with its low binding to human receptors on glycan array. C and D respectively show intense staining of alveolar section by mFC:LS and FC consistent with their high affinity binding to avian receptors.

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