Influenza virus assembly and release

Overview Fingerprint. Abstract Influenza A virus causes seasonal epidemics, sporadic pandemics and is a significant global health burden.

Access to Document Link to publication in Scopus. Link to the citations in Scopus. Fingerprint Dive into the research topics of 'Influenza virus assembly and budding'. Together they form a unique fingerprint. Isolation and characterization of the positive-sense replicative intermediate of a negative-strand RNA virus. Nucleic Acids Res 44 — J Virol 80 — Genetic trans-complementation establishes a new model for influenza virus RNA transcription and replication.

PLoS Pathog 5 :e Structural insight into cap-snatching and RNA synthesis by influenza polymerase. Nature —6. Cell 23 — J Virol 79 —8. RNA-free and ribonucleoprotein-associated influenza virus polymerases directly bind the serinephosphorylated carboxyl-terminal domain of host RNA polymerase II. The structural basis for cap binding by influenza virus polymerase subunit PB2. Nat Struct Mol Biol 15 —6. The cap-snatching endonuclease of influenza virus polymerase resides in the PA subunit. Crystal structure of an avian influenza polymerase PA N reveals an endonuclease active site.

Polyadenylation sites for influenza virus mRNA. J Virol 38 — J Virol 73 —6. An in vitro fluorescence based study of initiation of RNA synthesis by influenza B polymerase.

Nucleic Acids Res 45 — Influenza viruses and mRNA splicing: doing more with less. MBio 5 :e70— Sequence of interrupted and uninterrupted mRNAs and cloned DNA coding for the two overlapping nonstructural proteins of influenza virus.

Cell 21 — Nucleic Acids Res 9 — Influenza virus mRNA trafficking through host nuclear speckles. Nat Microbiol 1 Differences in the control of virus mRNA splicing during permissive or abortive infection with influenza A fowl plague virus.

J Gen Virol 65 Pt 1 — Regulated M1 mRNA splicing in influenza virus-infected cells. J Gen Virol 72 Pt 6 —8. Robb NC, Fodor E. J Gen Virol 93 —8. York A, Fodor E. Biogenesis, assembly, and export of viral messenger ribonucleoproteins in the influenza A virus infected cell. RNA Biol 10 — Nuclear import and assembly of influenza A virus RNA polymerase studied in live cells by fluorescence cross-correlation spectroscopy. J Virol 84 — Genome-wide analysis of influenza viral RNA and nucleoprotein association.

Phosphorylation at the homotypic interface regulates nucleoprotein oligomerization and assembly of the influenza virus replication machinery. PLoS Pathog 11 :e Ayllon J, Garcia-Sastre A. The NS1 protein: a multitasking virulence factor. Influenza virus targets the mRNA export machinery and the nuclear pore complex.

EMBO J 17 — A nuclear export signal in the matrix protein of influenza A virus is required for efficient virus replication. J Virol 86 — EMBO J 19 —8. A second CRM1-dependent nuclear export signal in the influenza A virus NS2 protein contributes to the nuclear export of viral ribonucleoproteins.

FEBS Lett —6. EMBO J 22 — A Rab and microtubule-dependent mechanism for cytoplasmic transport of influenza A virus viral RNA. J Virol 85 — RAB11A is essential for transport of the influenza virus genome to the plasma membrane. Apical transport of influenza A virus ribonucleoprotein requires Rabpositive recycling endosome. PLoS One 6 :e Influenza virus genome reaches the plasma membrane via a modified endoplasmic reticulum and Rabdependent vesicles. Nat Commun 8 Interaction of the influenza virus nucleoprotein with the cellular CRM1-mediated nuclear export pathway.

J Virol 75 — A functional sequence-specific interaction between influenza A virus genomic RNA segments. N-linked glycans direct the cotranslational folding pathway of influenza hemagglutinin. Mol Cell 11 — NH2-terminal hydrophobic region of influenza virus neuraminidase provides the signal function in translocation. Type II transmembrane domain hydrophobicity dictates the cotranslational dependence for inversion. Mol Biol Cell 25 — Integration of a small integral membrane protein, M2, of influenza virus into the endoplasmic reticulum: analysis of the internal signal-anchor domain of a protein with an ectoplasmic NH2 terminus.

Cell 71 — Deshaies RJ, Schekman R. A yeast mutant defective at an early stage in import of secretory protein precursors into the endoplasmic reticulum. Protein translocation across the endoplasmic reticulum. Isolation and characterization of the signal recognition particle receptor. J Cell Biol 95 —7. Substrate-specific translocational attenuation during ER stress defines a pre-emptive quality control pathway. Bowie JU. Solving the membrane protein folding problem.

X-ray structure of a protein-conducting channel. Molecular code for transmembrane-helix recognition by the Sec61 translocon. Polar residues and their positional context dictate the transmembrane domain interactions of influenza a neuraminidases.

Protein translocation across the rough endoplasmic reticulum. Cold Spring Harb Perspect Biol 5 :a The cotranslational maturation program for the type II membrane glycoprotein influenza neuraminidase.

N-linked carbohydrates act as lumenal maturation and quality control protein tags. Cell Biochem Biophys 41 — The number and location of glycans on influenza hemagglutinin determine folding and association with calnexin and calreticulin. Structure of the haemagglutinin membrane glycoprotein of influenza virus at 3 A resolution.

Structure of the influenza virus glycoprotein antigen neuraminidase at 2. The pandemic H1N1 neuraminidase N1 lacks the cavity in its active site. Nat Struct Mol Biol 17 —8. Influenza virus M2 integral membrane protein is a homotetramer stabilized by formation of disulfide bonds. Steps in maturation of influenza A virus neuraminidase. J Virol 69 —7. Assembly of subtype 1 influenza neuraminidase is driven by both the transmembrane and head domains. The influenza virus neuraminidase protein transmembrane and head domains have coevolved.

J Virol 89 — Influenza A viral replication is blocked by inhibition of the inositol-requiring enzyme 1 IRE1 stress pathway. Influenza induces endoplasmic reticulum stress, caspasedependent apoptosis, and c-Jun N-terminal kinase-mediated transforming growth factor-beta release in lung epithelial cells. Influenza a virus host shutoff disables antiviral stress-induced translation arrest. J Virol Methods — J Virol Methods :1—6. The signal sequence coding region promotes nuclear export of mRNA.

PLoS Biol 5 :e The NS1 protein from influenza virus stimulates translation initiation by enhancing ribosome recruitment to mRNAs. J Mol Biol — Major contribution of the RNA-binding domain of NS1 in the pathogenicity and replication potential of an avian H7N1 influenza virus in chickens. Virol J 15 Eukaryotic translation initiation factor 4GI is a cellular target for NS1 protein, a translational activator of influenza virus. Mol Cell Biol 20 — Influenza virus NS1 protein stimulates translation of the M1 protein.

J Virol 68 —7. J Virol 69 — Influenza viruses cause hemolysis and fusion of cells. Virology —7. Interaction of influenza virus hemagglutinin with target membrane lipids is a key step in virus-induced hemolysis and fusion at pH 5.

Influenza virus hemagglutinin with multibasic cleavage site is activated by furin, a subtilisin-like endoprotease. EMBO J 11 — J Clin Invest 80 —9. J Virol 80 —8. Proteolytic activation of the influenza virus hemagglutinin. Cleavage of influenza a virus hemagglutinin in human respiratory epithelium is cell associated and sensitive to exogenous antiproteases. J Virol 76 —9. Amantadine selection of a mutant influenza virus containing an acid-stable hemagglutinin glycoprotein: evidence for virus-specific regulation of the pH of glycoprotein transport vesicles.

Takeuchi K, Lamb RA. Influenza virus M2 protein ion channel activity stabilizes the native form of fowl plague virus hemagglutinin during intracellular transport. J Virol 68 —9. PLoS One 7 :e Lingwood D, Simons K. Lipid rafts as a membrane-organizing principle. Influenza virus assembly and budding. Veit M, Thaa B. Association of influenza virus proteins with membrane rafts.

Adv Virol Mutations at palmitylation sites of the influenza virus hemagglutinin affect virus formation. J Virol 68 — Acylation-mediated membrane anchoring of avian influenza virus hemagglutinin is essential for fusion pore formation and virus infectivity.

J Virol 79 — S acylation of the hemagglutinin of influenza viruses: mass spectrometry reveals site-specific attachment of stearic acid to a transmembrane cysteine. J Virol 82 — Influenza virus hemagglutinin concentrates in lipid raft microdomains for efficient viral fusion. Role of transmembrane domain and cytoplasmic tail amino acid sequences of influenza a virus neuraminidase in raft association and virus budding. J Virol 78 — Influenza virus assembly: effect of influenza virus glycoproteins on the membrane association of M1 protein.

Influenza virus assembly and lipid raft microdomains: a role for the cytoplasmic tails of the spike glycoproteins. Identification of the domains of the influenza A virus M1 matrix protein required for NP binding, oligomerization and incorporation into virions.

However, no mechanistic role for NP in budding has been determined. Due to its helical structure and ability to bind to membranes, M1 may possess an intrinsic ability to alter membrane curvature and cause membrane budding.

It is possible that during virus budding, association of M1 with the cytoplasmic tails of HA and NA recruits M1 to the membrane, where the ability of M1 to alter membrane curvature combines with the HA-mediated initiation of virus budding to increase the efficiency of virus budding.

Thus, the assembly of M1 at sites of budding, along with other viral proteins such as NP, may block M1 mediation of budding in a manner that is analogous to that of HA. As discussed below completion of virus budding requires an additional protein, M2, to mediate membrane scission and virion release. M2 is a 97 amino acid protein that associates in the membrane as a homotetramer Holsinger and Lamb, ; Sugrue and Hay, The 19 amino acid TM domain forms the pore of the ion channel Lamb et al.

Recent work has suggested that the M2 cytoplasmic tail, and specifically its amphipathic helix residues 46—62, may play an important role in virus assembly and budding Chen et al. Whereas earlier studies mapped the genetic requirement for filamentous virion formation to the M1 protein Bourmakina and Garcia-Sastre, ; Burleigh et al.

When M2 protein was reconstituted into large unilamellar vesicles containing high levels of cholesterol, which resemble lipidic virus budding domains, the M2 amphipathic helix induced negative membrane curvature Rossman et al. At sites of virus budding, this induction of negative curvature may stabilize the site of budding long enough to allow for filament polymerization Rossman et al.

It has been speculated that the cytoplasmic tail of M2, between resides 70—77, plays an important role in binding to M1 Chen et al. Thus, mutation of M2, such that it can no longer bind to M1, may impair filament formation by preventing the M2-mediated stabilization of the virus budding site. The M2 cytoplasmic tail was also shown to be important for the efficient production of infectious viral particles, as mutations between residues 70—77 impaired vRNP incorporation into budding virions Grantham et al.

However, it is not known if the cytoplasmic tail of M2 binds NP directly or if alterations in the M2-M1 interaction are responsible for the reduction in vRNP packaging. Additional evidence for the interaction between M2 and M1 comes from the observation that treatment of influenza virus-infected cells with the M2 ectodomain-specific monoclonal antibody mAb 14C2 causes a loss of filament formation Hughey et al.

Virus mutants that escape antibody growth restriction contain mutations in M1 or in the M2 cytoplasmic tail Hughey et al. Interestingly, it has been reported recently that M2 may also associate directly with HA in an M1-independent manner Thaa et al. Thus, the recruitment of M2 to sites of virus budding may involve associations with both M1 and HA. In addition to filament formation and vRNP recruitment, the interaction between M1 and M2, or M2 and HA, may play another important role during virus budding, the mediation of membrane scission.

While HA, and possibly M1, are capable of altering membrane curvature and initiating the budding event, membrane scission and the release of the budding virion requires the M2 protein Rossman et al.

It was reported that the influenza virus M1 protein sequence YRKL residues — fulfilled the criteria of a late domain, including position independence of the sequence and the ability to replace the sequence with a know late domain sequence, PTAP Hui et al. Further research has shown that whereas M1 does appear to interact with VPS28, influenza virus budding is not dependent on the host ESCRT complex, thus necessitating an alternate means of membrane scission Bruce et al.

The host ESCRT-III complex mediates membrane scission by assembling a spiral of the protein Snf7 around the neck of a budding vesicle, progressively constricting the budding neck and forcing membrane scission Wollert et al.

Recent work from our laboratory indicates that influenza virus utilizes the amphipathic helix of the M2 protein to alter membrane curvature at the budding neck of the virus Rossman et al. Modification of membrane curvature by proteins that contain amphipathic helixes is an established phenomenon Donaldson, ; Epand et al.

Interestingly, the M2 protein appears to modify membrane curvature in a cholesterol-dependant manner Rossman et al. The M2 cytoplasmic tail contains two partial, overlapping, cholesterol recognition amino acid consensus CRAC motifs and the ability of M2 to bind cholesterol has been demonstrated Rossman et al. However, when expressed in the absence of other viral proteins, M2 is localized to non-raft areas of the apical plasma membrane Leser and Lamb, ; Zhang et al.

It is speculated that binding to M1 may recruit M2 to the, lipid raft-enriched, sites of virus budding where M2 would then be able to bind cholesterol Chen et al. This cholesterol binding may stabilize the association of M2 at the site of virus budding, allowing for the incorporation of M2 into the budding virion. Additionally, M2-cholesterol association may allow for M2 to alter membrane curvature at the site of virus budding Rossman et al.

However, ablation of the CRAC domain only causes minor decreases in pathogenicity of the mutant influenza viruses in mice. Thus, the significance of cholesterol binding is not known Stewart et al. The M2 cytoplasmic tail also contains a caveolin-1 binding domain CBD and binding to caveolin-1 has been demonstrated both in vitro and in virus-infected cells Sun et al. Experiments utilizing large and giant unilamellar vesicles have shown that in a low cholesterol environment, equivalent to the bulk phase of the plasma membrane, reconstituted M2 appears to cause positive membrane curvature, while in the presence of high levels of cholesterol, such as those found in the lipid raft-enriched sites of virus budding, M2 mediates negative membrane curvature Rossman et al.

Thus, the M1-mediated recruitment of M2 to sites of virus budding may trigger the induction of negative membrane curvature which may stabilize the HA and M1 induction of positive membrane curvature caused during budding initiation. This stabilization may allow for virus filament formation Rossman et al. Interestingly, mutations of M2 that reduce the interaction with M1 also reduce the incorporation of NP into the budding virion Chen et al.

In a virus-infected cell, M2 localizes to the boundary between raft and bulk plasma membrane domains surrounding the sites of virus budding Rossman et al. The non-raft localized M2 is under represented in virions as compared to its high level of expression in cells Lamb et al.

During budding, perhaps due to its concentration at the lipid phase boundary, M2 will eventually be localized to the neck of the budding virion, at the boundary between the lipid raft-rich virion and the remaining bulk plasma membrane phase Rossman et al.

At this point, M2 in the lower-cholesterol environment of the plasma membrane, would cause positive membrane curvature Rossman et al. Positive membrane curvature at the neck of the budding virion would be sufficient to cause membrane scission, possibly through modification of the line tension between the two lipid phases, resulting in the release of the budding virus.

Although it is not possible to directly determine the number of M2 tetramers required to mediate membrane scission or the number of tetramers found at the neck of the budding virus, it has been estimated that by 6 hours post-infection there are 3. As there is extensive colocalization between M2 and HA at sites of virus budding Rossman et al. An alternative model of membrane scission and virus release has been proposed recently. The release of budding influenza virions was observed to be attenuated when the expression of the small GTP-binding protein Rab11 was reduced Bruce et al.

Rab11, and its interacting proteins, were also shown recently to be involved in the release of budding respiratory syncytial virus, and thus was considered to reflect an alternative means for membrane scission and virion release, though the mechanism for scission has not been determined Brock et al. However, Rab11 is also known to be involved in the trafficking of proteins to the apical membrane in polarized cells reviewed in Jing and Prekeris, , and siRNA knockdown of Rab11 expression reduced the levels of M2 found on the apical membrane during influenza virus infection Rossman et al.

Further studies are necessary to determine if Rab11 plays an active role in membrane scission during influenza virus infection or if Rab11 is essential for the proper transport of M2 which then mediates membrane scission and virion release.

Recent studies further support the idea of M2-mediated membrane scission. Mutation or deletion of M2 significantly attenuates the production of infectious virions as well as the release of virus particles Chen et al.

Examination of cells infected with mutant viruses that are deleted for the M2 protein, or contain truncations of the M2 cytoplasmic tail, show that although virus budding begins virus release is blocked. It appears that both spherical as well as filamentous strains of influenza virus require the M2 protein for membrane scission, as mutation of M2 in a spherical strain also results in a scission-defective morphology Iwatsuki-Horimoto et al. This premature triggering of membrane scission could cause virion release prior to the recruitment and organization of all required viral proteins and the RNPs, possibly explaining the reduced infectivity of the released virions Barman and Nayak, Given the high degree of conservation of the M2 protein and the observation that amphipathic helices from several different strains of influenza virus can alter membrane curvature, it appears that mediation of membrane scission is a highly conserved function of the M2 protein Rossman et al.

The mechanism of influenza virus budding and assembly has been investigated for many years. However, it has been difficult to generate a model of the mechanistic progressing of virus budding.

Perhaps one of the difficulties is the disconnect between VLP budding and virus budding. In many other model systems, VLP budding is thought to portray accurately the basic mechanism of virus budding. However, for influenza virus, there appear to be many inconsistencies between virus and VLP budding, such as the observation that influenza virus forms filamentous virions, while the VLPs are spherical Chen et al.

Single protein expression experiments show that HA Chen et al. This raises the question as to the nature of the driving force for influenza virus budding? The answer may not be as simple as with other viruses, rather multiple influenza virus proteins may all provide a driving force for budding. It is possible that the ability of multiple proteins to mediate budding may provide a level of redundancy, allowing the virus to survive loss of function in individual proteins to mediate budding.

Alternatively, the spatial-temporal organization of viral protein assembly may allow each protein to provide its additive effect on budding in a sequential manner driving budding in a defined, organized fashion.

Between the different viral proteins capable of mediating budding, only HA and NA appear capable of initiating the budding event. This leaves HA and NA to initiate the budding event. As HA and NA are both targeted to lipid raft domains and both proteins appear to be able to alter membrane curvature causing budding, the concentration of HA and NA in lipid rafts may serve to provide a local alteration in membrane curvature that starts the budding process Fig. Additionally, membrane-bound M1 may then mediate alterations in membrane curvature, further progressing the budding event.

This block in budding may necessitate M2-mediated membrane scission for completion. Model of Influenza Virus Budding. A The initiation of virus budding caused by clustering of HA shown in red and NA shown in orange in lipid raft domains. B Elongation of the budding virion caused by polymerization of the M1 protein, resulting in a polarized localization of the vRNPs. M2 shown in blue is recruited to the periphery of the budding virus though interactions with M1. C Membrane scission caused by the insertion of the M2 amphipathic helix at the lipid phase boundary, altering membrane curvature at the neck of the budding virus and leading to release of the budding virus.

D Overview of the budding of influenza viruses, showing the coalescence of HA and NA containing lipid rafts shown in yellow , the formation of a filamentous virion and membrane scission caused by M2 clustered at the neck of the budding virus. The delayed expression of M2 Zebedee et al. Furthermore, the recruitment of M2 to sites of budding, by M1, puts M2 in a cholesterol-rich environment, where M2 stabilizes the site of budding instead of causing membrane scission Fig.

This would allow for proper assembly of the budding virion before M2 is localized to the neck of the budding virion, placing it at the boundary between the lipid raft-enriched virion and the bulk plasma membrane phases Fig. At the budding neck, M2 may exert its own positive membrane curvature by inserting its amphipathic helix into the membrane and modifying the line tension between the two lipid phases.

This further alteration of membrane curvature may provide the final force needed to mediate membrane scission and the release of the budding virion Fig. Following the completion of membrane scission, the virion may still be tethered to the cell membrane due to the interaction of virion-associated HA and cell-surface sialic acid moieties. NA is then able to play the final role in virus budding, cleaving sialic acid off the cell surface, preventing the HA-receptor interaction and freeing the budded virion.

J Gen Virol 65 Pt 1 — Regulated M1 mRNA splicing in influenza virus-infected cells. J Gen Virol 72 Pt 6 —8. Robb NC, Fodor E. J Gen Virol —8. York A, Fodor E. Biogenesis, assembly, and export of viral messenger ribonucleoproteins in the influenza A virus infected cell. RNA Biol — Nuclear import and assembly of influenza A virus RNA polymerase studied in live cells by fluorescence cross-correlation spectroscopy.

Genome-wide analysis of influenza viral RNA and nucleoprotein association. Phosphorylation at the homotypic interface regulates nucleoprotein oligomerization and assembly of the influenza virus replication machinery.

Ayllon J, Garcia-Sastre A. The NS1 protein: a multitasking virulence factor. Influenza virus targets the mRNA export machinery and the nuclear pore complex. EMBO J — A nuclear export signal in the matrix protein of influenza A virus is required for efficient virus replication. EMBO J —8. A second CRM1-dependent nuclear export signal in the influenza A virus NS2 protein contributes to the nuclear export of viral ribonucleoproteins. FEBS Lett —6.

A Rab and microtubule-dependent mechanism for cytoplasmic transport of influenza A virus viral RNA. RAB11A is essential for transport of the influenza virus genome to the plasma membrane. Apical transport of influenza A virus ribonucleoprotein requires Rabpositive recycling endosome.

PLoS One 6:e Influenza virus genome reaches the plasma membrane via a modified endoplasmic reticulum and Rabdependent vesicles. Interaction of the influenza virus nucleoprotein with the cellular CRM1-mediated nuclear export pathway.

A functional sequence-specific interaction between influenza A virus genomic RNA segments. N-linked glycans direct the cotranslational folding pathway of influenza hemagglutinin. Mol Cell — NH2-terminal hydrophobic region of influenza virus neuraminidase provides the signal function in translocation. Type II transmembrane domain hydrophobicity dictates the cotranslational dependence for inversion. Mol Biol Cell — Integration of a small integral membrane protein, M2, of influenza virus into the endoplasmic reticulum: analysis of the internal signal-anchor domain of a protein with an ectoplasmic NH2 terminus.

Deshaies RJ, Schekman R. A yeast mutant defective at an early stage in import of secretory protein precursors into the endoplasmic reticulum. Protein translocation across the endoplasmic reticulum. Isolation and characterization of the signal recognition particle receptor. J Cell Biol —7. Substrate-specific translocational attenuation during ER stress defines a pre-emptive quality control pathway. Bowie JU.

Solving the membrane protein folding problem. X-ray structure of a protein-conducting channel. Molecular code for transmembrane-helix recognition by the Sec61 translocon. Polar residues and their positional context dictate the transmembrane domain interactions of influenza a neuraminidases.

Protein translocation across the rough endoplasmic reticulum. Cold Spring Harb Perspect Biol 5:a The cotranslational maturation program for the type II membrane glycoprotein influenza neuraminidase. N-linked carbohydrates act as lumenal maturation and quality control protein tags.

Cell Biochem Biophys — The number and location of glycans on influenza hemagglutinin determine folding and association with calnexin and calreticulin. Structure of the haemagglutinin membrane glycoprotein of influenza virus at 3 A resolution. Structure of the influenza virus glycoprotein antigen neuraminidase at 2. The pandemic H1N1 neuraminidase N1 lacks the cavity in its active site. Nat Struct Mol Biol —8.

Influenza virus M2 integral membrane protein is a homotetramer stabilized by formation of disulfide bonds. Steps in maturation of influenza A virus neuraminidase. J Virol —7. Assembly of subtype 1 influenza neuraminidase is driven by both the transmembrane and head domains. The influenza virus neuraminidase protein transmembrane and head domains have coevolved. Influenza A viral replication is blocked by inhibition of the inositol-requiring enzyme 1 IRE1 stress pathway.

Influenza induces endoplasmic reticulum stress, caspasedependent apoptosis, and c-Jun N-terminal kinase-mediated transforming growth factor-beta release in lung epithelial cells.

Influenza a virus host shutoff disables antiviral stress-induced translation arrest. J Virol Methods — J Virol Methods —6. The signal sequence coding region promotes nuclear export of mRNA.

PLoS Biol 5:e The NS1 protein from influenza virus stimulates translation initiation by enhancing ribosome recruitment to mRNAs. J Mol Biol — Major contribution of the RNA-binding domain of NS1 in the pathogenicity and replication potential of an avian H7N1 influenza virus in chickens.

Virol J Eukaryotic translation initiation factor 4GI is a cellular target for NS1 protein, a translational activator of influenza virus. Mol Cell Biol — Influenza virus NS1 protein stimulates translation of the M1 protein. Influenza viruses cause hemolysis and fusion of cells.

Virology —7. Interaction of influenza virus hemagglutinin with target membrane lipids is a key step in virus-induced hemolysis and fusion at pH 5. Influenza virus hemagglutinin with multibasic cleavage site is activated by furin, a subtilisin-like endoprotease.

J Clin Invest —9. Proteolytic activation of the influenza virus hemagglutinin. Cleavage of influenza a virus hemagglutinin in human respiratory epithelium is cell associated and sensitive to exogenous antiproteases. J Virol —9. Amantadine selection of a mutant influenza virus containing an acid-stable hemagglutinin glycoprotein: evidence for virus-specific regulation of the pH of glycoprotein transport vesicles.

Takeuchi K, Lamb RA. Influenza virus M2 protein ion channel activity stabilizes the native form of fowl plague virus hemagglutinin during intracellular transport. PLoS One 7:e Lingwood D, Simons K. Lipid rafts as a membrane-organizing principle. Influenza virus assembly and budding. Veit M, Thaa B. Association of influenza virus proteins with membrane rafts.

Adv Virol Mutations at palmitylation sites of the influenza virus hemagglutinin affect virus formation. Acylation-mediated membrane anchoring of avian influenza virus hemagglutinin is essential for fusion pore formation and virus infectivity. S acylation of the hemagglutinin of influenza viruses: mass spectrometry reveals site-specific attachment of stearic acid to a transmembrane cysteine.

Influenza virus hemagglutinin concentrates in lipid raft microdomains for efficient viral fusion. Role of transmembrane domain and cytoplasmic tail amino acid sequences of influenza a virus neuraminidase in raft association and virus budding. Influenza virus assembly: effect of influenza virus glycoproteins on the membrane association of M1 protein. Influenza virus assembly and lipid raft microdomains: a role for the cytoplasmic tails of the spike glycoproteins.

Identification of the domains of the influenza A virus M1 matrix protein required for NP binding, oligomerization and incorporation into virions.

Membrane curvature in cell biology: an integration of molecular mechanisms. Influenza virus hemagglutinin and neuraminidase, but not the matrix protein, are required for assembly and budding of plasmid-derived virus-like particles. Formation of virus-like particles from human cell lines exclusively expressing influenza neuraminidase.

Budding capability of the influenza virus neuraminidase can be modulated by tetherin. Structural analysis of the roles of influenza A virus membrane-associated proteins in assembly and morphology. The crystal structure of the influenza matrix protein M1 at neutral pH: M1-M1 protein interfaces can rotate in the oligomeric structures of M1. Influenza virus matrix protein M1 preserves its conformation with pH, changing multimerization state at the priming stage due to electrostatics.

Influenza A matrix protein M1 multimerizes upon binding to lipid membranes. Biophys J — The M1 matrix protein controls the filamentous phenotype of influenza A virus. Viral membrane scission. Annu Rev Cell Dev Biol — The influenza virus hemagglutinin cytoplasmic tail is not essential for virus assembly or infectivity.

Garcia-Sastre A, Palese P. The cytoplasmic tail of the neuraminidase protein of influenza A virus does not play an important role in the packaging of this protein into viral envelopes. Stewart SM, Pekosz A. Mutations in the membrane-proximal region of the influenza A virus M2 protein cytoplasmic tail have modest effects on virus replication. Air GM. Influenza neuraminidase. Influenza Other Respi Viruses — Colman PM. Influenza virus neuraminidase: structure, antibodies, and inhibitors.

Protein Sci — The 2. Mechanism-based covalent neuraminidase inhibitors with broad-spectrum influenza antiviral activity. Science —5. Structure of the catalytic and antigenic sites in influenza virus neuraminidase. Nature —4. Conversion of a class II integral membrane protein into a soluble and efficiently secreted protein: multiple intracellular and extracellular oligomeric and conformational forms.

A 2 N2 neuraminidase of the X-7 influenza virus recombinant: determination of molecular size and subunit composition of the active unit. Influenza virus sialidase: effect of calcium on steady-state kinetic parameters. Biochim Biophys Acta —