scholarly journals Hemagglutinin Stability and Its Impact on Influenza A Virus Infectivity, Pathogenicity, and Transmissibility in Avians, Mice, Swine, Seals, Ferrets, and Humans

Viruses ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 746
Author(s):  
Charles J. Russell
Keyword(s):  
Membrane Fusion ◽  
Influenza A ◽  
Structural Changes ◽  
Surface Glycoprotein ◽  
Virus Infectivity ◽  
Influenza A Viruses ◽  
Sea Mammals ◽  
Major Antigen ◽  
The Stability ◽  
Ha Protein

Genetically diverse influenza A viruses (IAVs) circulate in wild aquatic birds. From this reservoir, IAVs sporadically cause outbreaks, epidemics, and pandemics in wild and domestic avians, wild land and sea mammals, horses, canines, felines, swine, humans, and other species. One molecular trait shown to modulate IAV host range is the stability of the hemagglutinin (HA) surface glycoprotein. The HA protein is the major antigen and during virus entry, this trimeric envelope glycoprotein binds sialic acid-containing receptors before being triggered by endosomal low pH to undergo irreversible structural changes that cause membrane fusion. The HA proteins from different IAV isolates can vary in the pH at which HA protein structural changes are triggered, the protein causes membrane fusion, or outside the cell the virion becomes inactivated. HA activation pH values generally range from pH 4.8 to 6.2. Human-adapted HA proteins tend to have relatively stable HA proteins activated at pH 5.5 or below. Here, studies are reviewed that report HA stability values and investigate the biological impact of variations in HA stability on replication, pathogenicity, and transmissibility in experimental animal models. Overall, a stabilized HA protein appears to be necessary for human pandemic potential and should be considered when assessing human pandemic risk.

scholarly journals Matriptase, HAT, and TMPRSS2 Activate the Hemagglutinin of H9N2 Influenza A Viruses

2012 ◽  
Vol 87 (3) ◽  
pp. 1811-1820 ◽  
Author(s):  
Joanna Baron ◽  
Carolin Tarnow ◽  
Deborah Mayoli-Nüssle ◽  
Eva Schilling ◽  
Daniela Meyer ◽  
...  
Keyword(s):  
Cleavage Site ◽  
Influenza A ◽  
Surface Glycoprotein ◽  
Virus Infectivity ◽  
Kidney Cells ◽  
Cleavage Sites ◽  
Influenza A Viruses ◽  
Proteolytic Activation ◽  
Wide Range ◽  
Canine Kidney

ABSTRACTInfluenza A viruses of the subtype H9N2 circulate worldwide and have become highly prevalent in poultry in many countries. Moreover, they are occasionally transmitted to humans, raising concern about their pandemic potential. Influenza virus infectivity requires cleavage of the surface glycoprotein hemagglutinin (HA) at a distinct cleavage site by host cell proteases. H9N2 viruses vary remarkably in the amino acid sequence at the cleavage site, and many isolates from Asia and the Middle East possess the multibasic motifs R-S-S-R and R-S-R-R, but are not activated by furin. Here, we investigated proteolytic activation of the early H9N2 isolate A/turkey/Wisconsin/1/66 (H9-Wisc) and two recent Asian isolates, A/quail/Shantou/782/00 (H9-782) and A/quail/Shantou/2061/00 (H9-2061), containing mono-, di-, and tribasic HA cleavage sites, respectively. All H9N2 isolates were activated by human proteases TMPRSS2 (transmembrane protease, serine S1 member 2) and HAT (human airway trypsin-like protease). Interestingly, H9-782 and H9-2061 were also activated by matriptase, a protease widely expressed in most epithelia with high expression levels in the kidney. Nephrotropism of H9N2 viruses has been observed in chickens, and here we found that H9-782 and H9-2061 were proteolytically activated in canine kidney (MDCK-II) and chicken embryo kidney (CEK) cells, whereas H9-Wisc was not. Virus activation was inhibited by peptide-mimetic inhibitors of matriptase, strongly suggesting that matriptase is responsible for HA cleavage in these kidney cells. Our data demonstrate that H9N2 viruses with R-S-S-R or R-S-R-R cleavage sites are activated by matriptase in addition to HAT and TMPRSS2 and, therefore, can be activated in a wide range of tissues what may affect virus spread, tissue tropism and pathogenicity.

scholarly journals Plasticity of the Influenza Virus H5 HA Protein

mBio ◽  
2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Huihui Kong ◽  
David F. Burke ◽  
Tiago Jose da Silva Lopes ◽  
Kosuke Takada ◽  
Masaki Imai ◽  
...  
Keyword(s):  
Influenza Virus ◽  
Amino Acid ◽  
Mammalian Cells ◽  
Influenza A ◽  
Viral Antigen ◽  
Influenza Viruses ◽  
Influenza A Viruses ◽  
Highly Pathogenic ◽  
Antigenic Properties ◽  
Ha Protein

ABSTRACT Since the emergence of highly pathogenic avian influenza viruses of the H5 subtype, the major viral antigen, hemagglutinin (HA), has undergone constant evolution, resulting in numerous genetic and antigenic (sub)clades. To explore the consequences of amino acid changes at sites that may affect the antigenicity of H5 viruses, we simultaneously mutated 17 amino acid positions of an H5 HA by using a synthetic gene library that, theoretically, encodes all combinations of the 20 amino acids at the 17 positions. All 251 mutant viruses sequenced possessed ≥13 amino acid substitutions in HA, demonstrating that the targeted sites can accommodate a substantial number of mutations. Selection with ferret sera raised against H5 viruses of different clades resulted in the isolation of 39 genotypes. Further analysis of seven variants demonstrated that they were antigenically different from the parental virus and replicated efficiently in mammalian cells. Our data demonstrate the substantial plasticity of the influenza virus H5 HA protein, which may lead to novel antigenic variants. IMPORTANCE The HA protein of influenza A viruses is the major viral antigen. In this study, we simultaneously introduced mutations at 17 amino acid positions of an H5 HA expected to affect antigenicity. Viruses with ≥13 amino acid changes in HA were viable, and some had altered antigenic properties. H5 HA can therefore accommodate many mutations in regions that affect antigenicity. The substantial plasticity of H5 HA may facilitate the emergence of novel antigenic variants.

scholarly journals Targeting Hemagglutinin: Approaches for Broad Protection against the Influenza A Virus

Viruses ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 405 ◽  
Author(s):  
Zhang ◽  
Xu ◽  
Zhang ◽  
Liu ◽  
Xue ◽  
...  
Keyword(s):  
Influenza A Virus ◽  
Influenza A ◽  
Protective Efficacy ◽  
Structure And Function ◽  
Antigenic Drift ◽  
Influenza A Viruses ◽  
Universal Vaccine ◽  
Vaccine Candidates ◽  
And Function ◽  
Ha Protein

Influenza A viruses are dynamically epidemic and genetically diverse. Due to the antigenic drift and shift of the virus, seasonal vaccines are required to be reformulated annually to match with current circulating strains. However, the mismatch between vaccinal strains and circulating strains occurs frequently, resulting in the low efficacy of seasonal vaccines. Therefore, several “universal” vaccine candidates based on the structure and function of the hemagglutinin (HA) protein have been developed to meet the requirement of a broad protection against homo-/heterosubtypic challenges. Here, we review recent novel constructs and discuss several important findings regarding the broad protective efficacy of HA-based universal vaccines.

scholarly journals Influenza Hemagglutinin (HA) Stem Region Mutations That Stabilize or Destabilize the Structure of Multiple HA Subtypes

2015 ◽  
Vol 89 (8) ◽  
pp. 4504-4516 ◽  
Author(s):  
Lauren Byrd-Leotis ◽  
Summer E. Galloway ◽  
Evangeline Agbogu ◽  
David A. Steinhauer
Keyword(s):  
Membrane Fusion ◽  
Receptor Binding ◽  
Conformational Changes ◽  
Influenza A ◽  
Mutational Analysis ◽  
Host Cells ◽  
Influenza A Viruses ◽  
Pathogenic Potential ◽  
Additional Tool ◽  
Improved Stability

ABSTRACTInfluenza A viruses enter host cells through endosomes, where acidification induces irreversible conformational changes of the viral hemagglutinin (HA) that drive the membrane fusion process. The prefusion conformation of the HA is metastable, and the pH of fusion can vary significantly among HA strains and subtypes. Furthermore, an accumulating body of evidence implicates HA stability properties as partial determinants of influenza host range, transmission phenotype, and pathogenic potential. Although previous studies have identified HA mutations that can affect HA stability, these have been limited to a small selection of HA strains and subtypes. Here we report a mutational analysis of HA stability utilizing a panel of expressed HAs representing a broad range of HA subtypes and strains, including avian representatives across the phylogenetic spectrum and several human strains. We focused on two highly conserved residues in the HA stem region: HA2 position 58, located at the membrane distal tip of the short helix of the hairpin loop structure, and HA2 position 112, located in the long helix in proximity to the fusion peptide. We demonstrate that a K58I mutation confers an acid-stable phenotype for nearly all HAs examined, whereas a D112G mutation consistently leads to elevated fusion pH. The results enhance our understanding of HA stability across multiple subtypes and provide an additional tool for risk assessment for circulating strains that may have other hallmarks of human adaptation. Furthermore, the K58I mutants, in particular, may be of interest for potential use in the development of vaccines with improved stability profiles.IMPORTANCEThe influenza A hemagglutinin glycoprotein (HA) mediates the receptor binding and membrane fusion functions that are essential for virus entry into host cells. While receptor binding has long been recognized for its role in host species specificity and transmission, membrane fusion and associated properties of HA stability have only recently been appreciated as potential determinants. We show here that mutations can be introduced at highly conserved positions to stabilize or destabilize the HA structure of multiple HA subtypes, expanding our knowledge base for this important phenotype. The practical implications of these findings extend to the field of vaccine design, since the HA mutations characterized here could potentially be utilized across a broad spectrum of influenza virus subtypes to improve the stability of vaccine strains or components.

scholarly journals pH Optimum of Hemagglutinin-Mediated Membrane Fusion Determines Sensitivity of Influenza A Viruses to the Interferon-Induced Antiviral State and IFITMs

2017 ◽  
Vol 91 (11) ◽  
Author(s):  
Thomas Gerlach ◽  
Luca Hensen ◽  
Tatyana Matrosovich ◽  
Janina Bergmann ◽  
Michael Winkler ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Membrane Fusion ◽  
Influenza A ◽  
Target Cells ◽  
Viral Fusion ◽  
Influenza A Viruses ◽  
Ph Optimum ◽  
High Ph ◽  
Innate Defense ◽  
Antiviral State

ABSTRACT The replication and pathogenicity of influenza A viruses (IAVs) critically depend on their ability to tolerate the antiviral interferon (IFN) response. To determine a potential role for the IAV hemagglutinin (HA) in viral sensitivity to IFN, we studied the restriction of IAV infection in IFN-β-treated human epithelial cells by using 2:6 recombinant IAVs that shared six gene segments of A/Puerto Rico/8/1934 virus (PR8) and contained HAs and neuraminidases of representative avian, human, and zoonotic H5N1 and H7N9 viruses. In A549 and Calu-3 cells, viruses displaying a higher pH optimum of HA-mediated membrane fusion, H5N1-PR8 and H7N9-PR8, were less sensitive to the IFN-induced antiviral state than their counterparts with HAs from duck and human viruses, which fused at a lower pH. The association between a high pH optimum of fusion and reduced IFN sensitivity was confirmed by using HA point mutants of A/Hong Kong/1/1968-PR8 that differed solely by their fusion properties. Furthermore, similar effects of the viral fusion pH on IFN sensitivity were observed in experiments with (i) primary human type II alveolar epithelial cells and differentiated cultures of human airway epithelial cells, (ii) nonrecombinant zoonotic and pandemic IAVs, and (iii) preparations of IFN-α and IFN-λ1. A higher pH of membrane fusion and reduced sensitivity to IFN correlated with lower restriction of the viruses in MDCK cells stably expressing the IFN-inducible transmembrane proteins IFITM2 and IFITM3, which are known to inhibit viral fusion. Our results reveal that the pH optimum of HA-driven membrane fusion of IAVs is a determinant of their sensitivity to IFN and IFITM proteins. IMPORTANCE The IFN system constitutes an important innate defense against viral infection. Substantial information is available on how IAVs avoid detection by sensors of the IFN system and disable IFN signaling pathways. Much less is known about the ability of IAVs to tolerate the antiviral activity of IFN-induced cellular proteins. The IFN-induced proteins of the IFITM family block IAV entry into target cells and can restrict viral spread and pathogenicity. Here we show for the first time that the sensitivity of IAVs to the IFN-induced antiviral state and IFITM2 and IFITM3 proteins depends on the pH value at which the viral HA undergoes a conformational transition and mediates membrane fusion. Our data imply that the high pH optimum of membrane fusion typical of zoonotic IAVs of gallinaceous poultry, such as H5N1 and H7N9, may contribute to their enhanced virulence in humans.

scholarly journals Ode to Oseltamivir and Amantadine?

2006 ◽  
Vol 17 (1) ◽  
pp. 11-14 ◽  
Author(s):  
JM Conly ◽  
BL Johnston
Keyword(s):  
Influenza A ◽  
Antigenic Variation ◽  
Interleukin 1 ◽  
Influenza Viruses ◽  
Host Cells ◽  
Surface Glycoprotein ◽  
Influenza B ◽  
Influenza A Viruses ◽  
Epidemic Disease ◽  
Specific Antigens

Influenza A and B viruses are the two major types of influenza viruses that cause human epidemic disease. Influenza A viruses are further categorized into subtypes based on two surface antigens: hemagglutinin (H) and neuraminidase (N). Influenza B viruses are not categorized into subtypes (1). Influenza A viruses are found in many animal species, including humans, ducks, chickens, pigs, whales, horses and seals, whereas influenza B viruses circulate only among humans. The H antigen contains common and strain-specific antigens, demonstrates antigenic variation, and acts as a site of attachment of the virus to host cells to initiate infection (1). The N antigen contains subtype-specific antigens and also demonstrates antigenic variation between subtypes. It is a surface glycoprotein possessing enzymatic activity essential for viral replication in both influenza A and B viruses. The N antigen allows the release of newly produced virions from infected host cells, prevents the formation of viral aggregates after release from the host cells, and prevents viral inactivation by respiratory mucous (2,3). It is thought that this enzyme may also promote viral penetration into respiratory epithelial cells and may contribute to the pathogenicity of the virus by promoting production of proinflammatory cytokines such as interleukin-1 and tumour necrosis factor from macrophages (4-6).

scholarly journals Minor variants of swine H1N1 influenza viruses with enhanced polymerase activity and HA stability promote airborne transmission in ferrets

2021 ◽  
Author(s):  
Meng Hu ◽  
Jeremy Jones ◽  
Balaji Banoth ◽  
Chet R Ojha ◽  
Jeri Carol Crumpton ◽  
...  
Keyword(s):  
Risk Assessment ◽  
Deep Sequencing ◽  
Influenza A ◽  
H1n1 Influenza ◽  
Polymerase Activity ◽  
Protein Stabilization ◽  
Influenza Viruses ◽  
Influenza A Viruses ◽  
Airborne Transmission ◽  
Ha Protein

Understanding how animal influenza A viruses (IAVs) acquire airborne transmissibility in humans and ferrets is needed to prepare for and respond to pandemics. Previously, we showed that hemagglutinin (HA) protein stabilization promotes replication and airborne transmission in ferrets using swine H1N1 gamma strains P4 and G15 (Hu et al. 2020). Here, we show that a combination of enhanced polymerase activity and HA stability is necessary for efficient airborne transmission in ferrets and that minor variants containing both properties are quickly selected. P4 and G15 were found to have decreased polymerase activity and relatively poor HA stability, respectively. Polymerase-enhancing variant PA-S321 was selected in half of P4 isolates that airborne-transmitted in ferrets. HA-stabilizing variant HA1-S210 was selected in all G15-inoculated ferrets and was transmitted. With an efficient polymerase and a stable HA, purified G15-HA1-S210 had earlier and higher peak titers in inoculated ferrets and was recovered at a higher frequency after airborne transmission than P4 and G15. Pandemic risk-assessment studies may benefit from deep sequencing capable of identifying minor variants with human-adapted traits.

scholarly journals Insertions of codons encoding basic amino acids in H7 hemagglutinins of influenza A viruses occur by recombination with RNA at hotspots near snoRNA binding sites

2020 ◽  
Author(s):  
Alexander P. Gultyaev ◽  
Monique I. Spronken ◽  
Mathis Funk ◽  
Ron A.M. Fouchier ◽  
Mathilde Richard
Keyword(s):  
Amino Acids ◽  
Cleavage Site ◽  
Influenza A ◽  
Rna Recombination ◽  
Influenza A Viruses ◽  
Rna Sequences ◽  
Rna Molecules ◽  
Basic Amino Acids ◽  
Molecular Determinant ◽  
Ha Protein

ABSTRACTThe presence of multiple basic amino acids in the protease cleavage site of the hemagglutinin (HA) protein is the main molecular determinant of virulence of highly pathogenic avian influenza (HPAI) viruses. Recombination of HA RNA with other RNA molecules of host or virus origin is a dominant mechanism of multi basic cleavage site (MBCS) acquisition for H7 subtype HA. Using alignments of HA RNA sequences from documented cases of MBCS insertion due to recombination, we show that such recombination with host RNAs is most likely to occur at particular hotspots in ribosomal RNAs (rRNAs), transfer RNAs (tRNAs) and viral RNAs. The locations of these hotspots in highly abundant RNAs indicate that RNA recombination is facilitated by the binding of small nucleolar RNA (snoRNA) near the recombination points.

scholarly journals An Oleanolic Acid Derivative Inhibits Hemagglutinin-Mediated Entry of Influenza A Virus

Viruses ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 225 ◽  
Author(s):  
Mengdie Ye ◽  
Yixian Liao ◽  
Li Wu ◽  
Wenbao Qi ◽  
Namrta Choudhry ◽  
...  
Keyword(s):  
Membrane Fusion ◽  
Conformational Changes ◽  
Influenza A ◽  
Dissociation Constants ◽  
Early Stage ◽  
Dependent Manner ◽  
Influenza A Viruses ◽  
Endosomal Membrane ◽  
Chicken Erythrocytes ◽  
Dose Dependent

Influenza A viruses (IAV) have been a major public health threat worldwide, and options for antiviral therapy become increasingly limited with the emergence of drug-resisting virus strains. New and effective anti-IAV drugs, especially for highly pathogenic influenza, with different modes of action, are urgently needed. The influenza virus glycoprotein hemagglutinin (HA) plays critical roles in the early stage of virus infection, including receptor binding and membrane fusion, making it a potential target for the development of anti-influenza drugs. In this study, we show that OA-10, a newly synthesized triterpene out of 11 oleanane-type derivatives, exhibited significant antiviral activity against four different subtypes of IAV (H1N1, H5N1, H9N2 and H3N2) replications in A549 cell cultures with EC50 ranging from 6.7 to 19.6 μM and a negligible cytotoxicity (CC50 > 640 μM). It inhibited acid-induced hemolysis in a dose-dependent manner, with an IC50 of 26 µM, and had a weak inhibition on the adsorption of H5 HA to chicken erythrocytes at higher concentrations (≥40 µM). Surface plasmon resonance (SPR) analysis showed that OA-10 interacted with HA in a dose-dependent manner with the equilibrium dissociation constants (KD) of the interaction of 2.98 × 10−12 M. Computer-aided molecular docking analysis suggested that OA-10 might bind to the cavity in HA stem region which is known to undergo significant rearrangement during membrane fusion. Our results demonstrate that OA-10 inhibits H5N1 IAV replication mainly by blocking the conformational changes of HA2 subunit required for virus fusion with endosomal membrane. These findings suggest that OA-10 could serve as a lead for further development of novel virus entry inhibitors to prevent and treat IAV infections.

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

2007 ◽  
Vol 88 (12) ◽  
pp. 3209-3213 ◽  
Author(s):  
Natalie J. McDonald ◽  
Catherine B. Smith ◽  
Nancy J. Cox
Keyword(s):  
Amino Acid ◽  
Influenza A ◽  
Reverse Genetics ◽  
Selective Advantage ◽  
H1n1 Influenza ◽  
Antigenic Drift ◽  
Surface Glycoprotein ◽  
Single Amino Acid ◽  
Influenza A Viruses ◽  
Sequence Comparisons

Two genetically distinct lineages of H1N1 influenza A viruses, circulated worldwide before 1994, were antigenically indistinguishable. In 1994, viruses emerged in China, including A/Beijing/262/95, with profound antigenic differences from the contemporary circulating H1N1 strains. Haemagglutinin sequence comparisons of either a predecessor virus, A/Hebei/52/94, or one representative of the cocirculating A/Bayern/7/95-like clade, A/Shenzhen/227/95, revealed a deletion of K at position 134 (H3 numbering) in the antigenic variants. The K134 deletion conferred a selective advantage to the Chinese deletion lineage, such that it eventually gave rise to currently circulating H1 viruses. Using reverse genetics to generate viruses with either an insertion or deletion of aa 134, we have confirmed that the K134 deletion, rather than a constellation of sublineage specific amino acid changes, was sufficient for the antigenic difference observed in the Chinese deletion lineage, and reinsertion of K134 revealed the requirement of a compatible neuraminidase surface glycoprotein for viral growth.

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