Crystal Structure of Unliganded Influenza B Virus Hemagglutinin

Abstract

Here we report the crystal structure of hemagglutinin (HA) from influenza B/Hong Kong/8/73 (B/HK) virus determined to 2.8 Å. At a sequence identity of ϳ25% to influenza A virus HAs, B/HK HA shares a similar overall structure and domain organization. More than two dozen amino acid substitutions on influenza B virus HAs have been identified to cause antigenicity alteration in site-specific mutants, monoclonal antibody escape mutants, or field isolates. Mapping these substitutions on the structure of B/HK HA reveals four major epitopes, the 120 loop, the 150 loop, the 160 loop, and the 190 helix, that are located close in space to form a large, continuous antigenic site. Moreover, a systematic comparison of known HA structures across the entire influenza virus family reveals evolutionarily conserved ionizable residues at all regions along the chain and subunit interfaces. These ionizable residues are likely the structural basis for the pH dependence and sensitivity to ionic strength of influenza HA and hemagglutinin-esterase fusion proteins.Influenza virus is a negative-stranded RNA virus belonging to the Orthomyxoviridae family. Three types of influenza viruses have been detected: A, B, and C. They all have a major surface glycoprotein, hemagglutinin (HA) for influenza A and B viruses and hemagglutinin-esterase fusion (HEF) protein for influenza C virus (2,20,85,98). Infections caused by influenza A and B viruses remain a major source of human morbidity and mortality worldwide (13, 90).Influenza B virus circulates exclusively in humans and seals (66), with no subtypes. The first isolated influenza B virus strain was B/Lee/40 (44). Currently, there are two major phylogenetic lineages found in circulation: B/Victoria/2/87 (B/VI) like and B/Yamagata/16/88 (B/YM) like (41,77,83). Despite the lack of subtypes, influenza B virus undergoes antigenic variation through genetic reassortment among cocirculating strains of different lineages and antigenic drift from cumulative mutations (17,48,49,56,70,83,101). Influenza B virus HAs have a mutational rate about five times slower than that observed for influenza A virus HAs (3,10,15,19,34,41,44,45,81,94,101). The antigenic structures of influenza B virus HAs have been studied by sequence analysis of both naturally occurring variants and antibody-selected escape variants (5,6,10,35,44,45,51,76,77,94,96), using the structure of influenza A H3 HA as a reference (100). However, given the rather low sequence identity between influenza A and B virus HAs, ϳ20% for HA 1 , which is the primary target for antigenic variation, it is hard to define accurately the antigenic sites in this fashion.We have recently reported two crystal structures of influenza B/Hong Kong/8/73 virus HA (referred to as B/HK HA herein) in complex with human and avian receptor analogs (95). Comparison of these structures with those of influenza A virus HAs provided a structural basis for the receptor-binding properties of influenza A and B virus HAs and suggested the role of residue 222 (H3 numbering) as a key an...

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

“…1A). Each H17 HA monomer has six disulfides that are conserved in other influenza A virus HAs, five of which are conserved with influenza B virus HAs, which also have two unique disulfide bonds (10). Consistent with phylogenetic analysis that positions GU10-060 H17 in influenza A group 1 HAs (1), superimposing GU10-060 HA on other HA structures by individual domains reveals that the H17 HA is slightly more closely related to group 1 H1 (PDB ID code 3UBQ), H2 (3KU6), H5 (2FK0), and H9 (1JSD) with C α rmsd values of 1.9-2.2 Å (HA1), 0.9-1.2 Å (HA2), and 1.8-2.2 Å (HA monomer) than to group 2 H3 (2HMG), H7(1TI8), and H14 (3EYJ) with rmsd values of 2.3-2.4 Å (HA1), 1.4 Å (HA2), and 2.4-2.5 Å (HA monomer) (SI Appendix, Table S1).…”

Protein homology modeling and structure-function relationship of 2009 swine influenza virus hemagglutinin (HA1): more human than swine

“…It is HA1, which is mainly involved in the receptor binding, whereas HA2 is primarily involved in membrane fusion activities (Shangguan et al 1998). To date structural information of HA of all the three influenza viruses A, B and C have been reported, for instance HAs of human H3 (Wilson et al 1981), swine H9 (Ha et al 2001(Ha et al , 2002, avian H5 (Ha et al 2001(Ha et al , 2002Stevens et al 2006), H1 of 1918 influenza virus (Gamblin et al 2004;Stevens et al 2004), HA1 of influenza B (Tung et al 2004;Wang et al 2008) and HA-esterase fusion protein (Rosenthal et al 1998). This repertoire of studies strongly indicates the importance of HA in the infectivity and pathogenesis rendered by the virus.…”

Influence of single amino acid substitutions in the hemagglutinin on the antigenic and receptor-binding properties of influenza virus B/Florida/04/2006 of Yamagata-like evolutionary lineage

“…This position is located in the HA helix 190 [14] which forms the antigenic site BB1 [15]. The escape mutant, selected by using the mAb 9A3, has the amino acid substitution 242 (227) Ser→Arg.…”