Hemagglutinin homologue from H17N10 bat influenza virus exhibits divergent receptor-binding and pH-dependent fusion activities

Abstract

Bat influenza virus H17N10 represents a distinct lineage of influenza A viruses with gene segments coding for proteins that are homologs of the surface antigens, hemagglutinin (HA) and neuraminidase (NA). Our recent study of the N10 NA homolog revealed an NA-like structure, but with a highly divergent putative active site exhibiting little or no NA activity, and provided strong motivation for performing equivalent structural and functional analyses of the H17 HA protein. The overall structure of the H17 HA homolog from A/little yellow-shouldered bat/Guatemala/060/2010 at 3.18 Å resolution is very similar to other influenza HAs, with a putative receptor-binding site containing some conserved aromatic residues that form the base of the sialic acid binding site. However, the rest of the H17 receptor-binding site differs substantially from the other HA subtypes, including substitution of other conserved residues associated with receptor binding. Significantly, electrostatic potential analyses reveal that this putative receptor-binding site is highly acidic, making it unfavorable to bind any negatively charged sialylated receptors, consistent with the recombinant H17 protein exhibiting no detectable binding to sialylated glycans. Furthermore, the fusion mechanism is also distinct; trypsin digestion with recombinant H17 protein, when exposed to pH 4.0, did not degrade the HA1 and HA2, in contrast to other HAs. These distinct structural features and functional differences suggest that the H17 HA behaves very differently compared with other influenza HAs.crystal structure | evolution | infection | protease susceptibility | viral entry I nfluenza is an infectious disease of birds and mammals caused by influenza virus, an RNA virus of the Orthomyxoviridae family. Three types of influenza virus, A, B, and C, are known. Influenza A virus infects a wide range of avian and mammalian species and is the major cause of annual human epidemics and occasional pandemics. Based on the antigenic properties of the two surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA), type A viruses can be classified into multiple subtypes. With the recent discovery of the H17N10 subtype of bat influenza A viruses (1), 17 subtypes of HA (H1-17) and 10 subtypes of NA (N1-10) have been found to circulate in avian and/or mammalian hosts. The H17N10 virus expands the species that can be infected by influenza virus to bats, which account for approximately onefourth of all mammalian species and have been shown to be a reservoir for multiple emerging viruses (2).In influenza virus infection, the HA is responsible for binding of virus to sialic acid-containing receptors on host cell surface glycoproteins and glycolipids, internalization of the virus, and subsequently membrane fusion within the endosome of the infected cell. Following virus replication, the receptor-cleavage enzyme, NA, removes sialic acid from glycans on target cell surfaces as well as from newly formed budding virions so that the progeny viruses can be released and infect other...

The NS1 gene from bat-derived influenza-like virus H17N10 can be rescued in influenza A PR8 backbone

“…Considering the interaction between HA and NA and their importance for infecting cells, several attempts to rescue a reassortant with HA and NA from PR8 and the other six gene segments from H17N10 were unsuccessful, which is consistent with the results from previous studies (Juozapaitis et al, 2014;Zhou et al, 2014). We did not perform these experiments with HA and NA from H17N10 and the other six segments from PR8, considering that the receptors for H17N10 HA and NA are still unknown and that HA was unable to bind any known cell line Sun et al, 2013;Zhu et al, 2012Zhu et al, , 2013. The combination of PB2, PB1, PA and NP from H17N10 together with the other four segments from PR8 did not result in the production of replicative influenza viruses either, even though polymerase activity of the ribonuclear protein (RNP) complex was confirmed in human cells with minigenome reporter assay (Tong et al, 2012, Juozapaitis et al, 2014, which was reproduced in our study (data not shown).…”

“…Previous research has demonstrated that the bat-derived neuraminidase-like N10/N11 and haemagglutinin H17/H18 have different functions compared to their homologues in other influenza viruses . N10 and N11 lack sialidase activity on tested sialic-acidcontaining oligosaccharides Tong et al, 2013;Zhu et al, 2012), and the H17 and H18 proteins did not bind to the canonical sialic acid receptors Tong et al, 2013;Zhu et al, 2013). These results suggest that H17N10 and H18N11 are influenza-like viruses that are related to categorized influenza A viruses but seem incompatible in function and reassortment capability.…”

Structure and receptor-binding properties of an airborne transmissible avian influenza A virus hemagglutinin H5 (VN1203mut)

“…The surface glycoprotein hemagglutinin (HA) is responsible for virus entry and fusion by binding to the cellular receptor, sialic acid (SA) (Rogers et al, 1983). There are 16 serotypes of HA to date with a newly identifi ed H17 from bat whose function is distinct (Tong et al, 2012;Sun et al, 2013;Zhu et al, 2013). HA is one of the major genetic traits for interspecies transmission (Neumann et al, 2009).…”

Identification of Novel Fusion Inhibitors of Influenza A Virus by Chemical Genetics

“…These fusion inhibitors can be subdivided into inhibitors of the group 1 HAs and inhibitors of the group 2 HAs (13). Fusion inhibitors targeting group 1 HAs include CL-61917, CL-385319, and CL-62554 (15), Stachyflin (16), BMY-27709 (17), LY-180299 (18), RO5464466 and RO5487624 (19), and N-(1-thia-4-azaspiro [4.5]decan-4-yl) carboxamide inhibitors (19), while TBHQ (20,21) and S19 and C22 (22) are the currently known fusion inhibitors for group 2 HAs. Recently, arbidol (23) was proposed to be a fusion inhibitor of both group 1 and group 2 HAs.…”