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Filamentous versus Spherical Morphology: A Case Study of the Recombinant A/WSN/33 (H1N1) Virus
Larisa V Kordyukova1, Ramil R Mintaev2,3, Artyom A Rtishchev2
1Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119991Moscow, Russia.
Abstract:
Influenza A virus is a serious human pathogen that assembles enveloped virions on the plasma membrane of the host cell. The pleiomorphic morphology of influenza A virus, represented by spherical, elongated, or filamentous particles, is important for the spread of the virus in nature. Using fixative protocols for sample preparation and negative staining electron microscopy, we found that the recombinant A/WSN/33 (H1N1) (rWSN) virus, a strain considered to be strictly spherical, may produce filamentous particles when amplified in the allantoic cavity of chicken embryos. In contrast, the laboratory WSN strain and the rWSN virus amplified in Madin-Darby canine kidney cells exhibited a spherical morphology. Next-generation sequencing (NGS) suggested a rare Ser126Cys substitution in the M1 protein of rWSN, which was confirmed by the mass spectrometric analysis. No structurally relevant substitutions were found by NGS in other proteins of rWSN. Bioinformatics algorithms predicted a neutral structural effect of the Ser126Cys mutation. The mrWSN_M1_126S virus generated after the introduction of the reverse Cys126Ser substitution exhibited a similar host-dependent partially filamentous phenotype. We hypothesize that a shortage of some as-yet-undefined cellular components involved in virion budding and membrane scission may result in the appearance of filamentous particles in the case of usually "nonfilamentous" virus strains.
Insights
Influenza A virus can form filamentous particles, challenging its typical spherical shape. This morphology change, linked to a specific M1 protein mutation, may depend on host cell factors during virus budding.
Area of Science:
- Virology
- Cell Biology
- Structural Biology
Background:
- Influenza A virus (IAV) is a significant human pathogen.
- IAV virions exhibit pleomorphic morphology (spherical, elongated, filamentous), crucial for viral spread.
- The recombinant A/WSN/33 (H1N1) (rWSN) strain is typically considered spherical.
Purpose of the Study:
- To investigate the morphological variations of the rWSN influenza A virus strain.
- To identify potential genetic or cellular factors influencing IAV particle shape.
Main Methods:
- Negative staining electron microscopy (EM) with specific fixative protocols.
- Next-generation sequencing (NGS) for genetic analysis.
- Mass spectrometry for protein analysis.
- Bioinformatics for predicting mutation effects.
Main Results:
- The rWSN virus produced filamentous particles when amplified in chicken embryos, unlike its spherical form in cell culture.
- NGS and mass spectrometry identified a Ser126Cys substitution in the M1 protein of rWSN.
- Reintroducing the original Ser126 residue reversed the filamentous phenotype, confirming the mutation's role.
- Bioinformatics predicted a neutral structural effect for the Ser126Cys mutation.
Conclusions:
- Host-dependent factors, potentially related to cellular components involved in virion budding and membrane scission, influence influenza A virus morphology.
- A specific M1 protein mutation (Ser126Cys) can induce a partially filamentous phenotype in an otherwise spherical IAV strain.
- This suggests that environmental or cellular conditions can alter viral morphology, impacting its natural spread.
