Studies of Two Kinds of Virus Particles Which Comprise Influenza A2 Virus Strains

Choppin, Purnell W.; Murphy, James S.; Tamm, Igor

doi:10.1084/jem.112.5.945

Cited by 77 publications

(47 citation statements)

References 21 publications

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“…The ability to form filaments and spheres is similar to the observation that influenza virus forms both types of particles, depending on culture conditions and cellular or viral factors (3,6,10,24,27,31,40,41,44). Thus, there is support for the idea that mixed morphogenetic populations of particles can be formed from identical viral structural components.…”

Section: Discussionsupporting

confidence: 67%

Overlapping Roles of the Rous Sarcoma Virus Gag p10 Domain in Nuclear Export and Virion Core Morphology

Scheifele¹,

Kenney

Cairns

et al. 2007

J Virol

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Nucleocytoplasmic shuttling of the Rous sarcoma virus (RSV) Gag polyprotein is an integral step in virus particle assembly. A nuclear export signal (NES) was previously identified within the p10 domain of RSV Gag. Gag mutants containing deletions of the p10 NES or mutations of critical hydrophobic residues at positions 219, 222, 225, or 229 become trapped within the nucleus and exhibit defects in the efficiency of virus particle release. To investigate other potential roles for Gag nuclear trafficking in RSV replication, we created viruses bearing NES mutant Gag proteins. Viruses carrying p10 mutations produced low levels of particles, as anticipated, and those particles that were released were noninfectious. The p10 mutant viruses contained approximately normal amounts of Gag, Gag-Pol, and Env proteins and genomic viral RNA (vRNA), but several major structural defects were found. Thin-section transmission electron microscopy revealed that the mature particles appeared misshapen, while the viral cores were cylindrical, horseshoe-shaped, or fragmented, with some particles containing multiple small, electron-dense aggregates. Immature virus-like particles produced by the expression of Gag proteins bearing p10 mutations were also aberrant, with both spherical and tubular filamentous particles produced. Interestingly, the secondary structure of the encapsidated vRNA was altered; although dimeric vRNA was predominant, there was an additional high-molecular-weight fraction. Together, these results indicate that the p10 NES domain of Gag is critical for virus replication and that it plays overlapping roles required for the nuclear shuttling of Gag and for the maintenance of proper virion core morphology.Retroviral assembly is directed by the viral Gag polyprotein precursor. Despite containing very little sequence homology, all Gag proteins share three canonical domains, the MA (matrix), CA (capsid), and NC (nucleocapsid) domains, as well as additional regions that vary for each retrovirus. Immature virus particles contain unprocessed Gag and Gag-Pol fusion proteins arranged in a concentric array just inside the viral envelope, with the NC domain of Gag toward the center, bound to the dimeric, positive-sense viral RNA (vRNA) genome (4, 18, 51). The cleavage of Gag during the maturation process occurs during or immediately after budding, leading to a dramatic change in morphology, with the appearance of an electrondense core near the particle center. This dense core is comprised of vRNA coated by the NC protein, together forming the ribonucleoprotein (RNP) complex. The RNP is enclosed by a shell composed of CA multimers forming the virion core, which is in turn surrounded by the MA protein in association with the lipid envelope (reviewed in references 45 and 46). The molecular events that govern RNP and core formation during virus assembly and maturation are still not well understood.Functional mapping of the Gag polyprotein identified three discrete motifs, known as assembly domains, that coordinate virion formation and...

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Section: Discussionsupporting

confidence: 67%

Overlapping Roles of the Rous Sarcoma Virus Gag p10 Domain in Nuclear Export and Virion Core Morphology

Scheifele¹,

Kenney

Cairns

et al. 2007

J Virol

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“…Our finding that the footprint of the regions on native HA trimers that interact with C179 closely matches the footprints identified by X-ray crystallography for the binding of other stem region antibodies suggests a conserved strategy of different stem antibodies to access this region of HA on native virions. The demonstration of similar structures of the complex on spherical and filamentous virions suggests that stem region antibodies elicited using spherical vaccine platforms (e.g., virus-like particles) are able to target stem regions on filamentous influenza forms that have been observed in influenza isolates for almost 70 years (35)(36)(37). An important conclusion that can be drawn from our structural analysis results is that the majority of virion-bound HA is accessible to a broadly neutralizing anti-stem antibody.…”

Section: Discussionmentioning

confidence: 53%

Structure and accessibility of HA trimers on intact 2009 H1N1 pandemic influenza virus to stem region-specific neutralizing antibodies

Harris

Meyerson

Matsuoka³

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

106

113

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Rapid antigenic variation of HA, the major virion surface protein of influenza A virus, remains the principal challenge to the development of broader and more effective vaccines. Some regions of HA, such as the stem region proximal to the viral membrane, are nevertheless highly conserved across strains and among most subtypes. A fundamental question in vaccine design is the extent to which HA stem regions on the surface of the virus are accessible to broadly neutralizing antibodies. Here we report 3D structures derived from cryoelectron tomography of HA on intact 2009 H1N1 pandemic virions in the presence and absence of the antibody C179, which neutralizes viruses expressing a broad range of HA subtypes, including H1, H2, H5, H6, and H9. By fitting previously derived crystallographic structures of trimeric HA into the density maps, we deduced the locations of the molecular surfaces of HA involved in interaction with C179. Using computational methods to distinguish individual unliganded HA trimers from those that have bound C179 antibody, we demonstrate that ∼75% of HA trimers on the surface of the virus have C179 bound to the stem domain. Thus, despite their close packing on the viral membrane, the majority of HA trimers on intact virions are available to bind anti-stem antibodies that target conserved HA epitopes, establishing the feasibility of universal influenza vaccines that elicit such antibodies.envelope glycoproteins | subvolume averaging | virus structure | hemagglutunin | cryo-electron microscopy

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“…2A to H and Q). This result was surprising, as previous studies have reported conversion to a predominantly spherical morphology in some strains in 10 passages or fewer (9).…”

Section: Human Clinical Influenza Virus Isolates Produce Filamentous mentioning

confidence: 55%

“…Early studies revealed that filamentous strains gradually become spherical following repeated passage in embryonated chicken eggs (ECEs) (8,9). Whether this conversion also occurs upon passage in MDCK cells is unclear, as we were unable to find data on this point reported in the literature.…”

mentioning

confidence: 84%

Spherical Influenza Viruses Have a Fitness Advantage in Embryonated Eggs, while Filament-Producing Strains Are Selected In Vivo

Seladi-Schulman

Steel

Lowen

2013

J Virol

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Influenza viruses can take on two distinct morphologies: filamentous or spherical. While the functional significance of each virion type is unclear, filaments are generally observed in low-passage-number isolates, while an exclusively spherical morphology is seen in strains grown extensively in laboratory substrates. Previous studies have shown that filamentous morphology is lost upon passage in eggs. The fact that the filamentous morphology is maintained in nature but not in the laboratory suggests that filaments provide an advantage in the host that is not necessary for growth in laboratory substrates. To test this hypothesis and identify naturally occurring mutations that alter morphology, we examined the effect of serial adaptation in eggs, MDCK cells, and guinea pigs. Two filamentous strains, A/Netherlands/602/2009 (H1N1) and A/Georgia/M5081/2012 (H1N1), were passaged in eggs and MDCK cells. Conversely, the spherical laboratory strain A/Puerto Rico/8/1934 (H1N1) was passaged in guinea pigs. We found that although passage in eggs and MDCK cells can lead to a loss of filaments, an exclusively spherical morphology is not required for highly efficient growth in either substrate. We did, however, identify two point mutations in the matrix of egg passage 10 isolates that confer spherical morphology and increased growth in eggs. In contrast, serial passage in guinea pigs resulted in the selection of filament-forming variants. Sequencing revealed point mutations to the PR8 matrix that, when introduced individually, yielded filaments. These findings suggest a functional role for filaments in the infected host and expand the breadth of mutations known to affect influenza virus shape.

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Studies of Two Kinds of Virus Particles Which Comprise Influenza A2 Virus Strains

Cited by 77 publications

References 21 publications

Overlapping Roles of the Rous Sarcoma Virus Gag p10 Domain in Nuclear Export and Virion Core Morphology

Overlapping Roles of the Rous Sarcoma Virus Gag p10 Domain in Nuclear Export and Virion Core Morphology

Structure and accessibility of HA trimers on intact 2009 H1N1 pandemic influenza virus to stem region-specific neutralizing antibodies

Spherical Influenza Viruses Have a Fitness Advantage in Embryonated Eggs, while Filament-Producing Strains Are Selected In Vivo

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