Specific Nucleoprotein Residues Affect Influenza Virus Morphology

Abstract

Influenza virus strains are often pleiomorphic, a characteristic that is largely attributed to specific residues in matrix protein 1 (M1). Although the mechanism by which M1 controls virion morphology has not yet been defined, it is suggested that the M1 interaction with other viral proteins plays an important role. In this study, we rescued recombinant virus WSN-AichiM1 containing the spherical A/WSN/33 (WSN) backbone and the M1 protein from A/Aichi/2/68 (Aichi). Aichi M1 differs from WSN M1 by 7 amino acids but includes those identified to be responsible for filamentous virion formation. Interestingly, Aichi virus produced spherical virions, while WSN-AichiM1 exhibited a long filamentous morphology, as detected by immunofluorescence and electron microscopy. Additional incorporation of Aichi nucleoprotein (NP) but not the hemagglutinin (HA), neuraminidase (NA), or M2 gene to WSN-AichiM1 abrogated filamentous virion formation, suggesting that specific M1-NP interactions affect virion morphology. Further characterization of viruses containing WSN/Aichi chimeric NPs identified residues 214, 217, and 253 of Aichi NP as necessary and sufficient for the formation of spherical virions. NP residues 214 and 217 localize at the minor groove between the two opposite-polarity NP helical strands of viral ribonucleocapsids, and residue 253 also localizes near the surface of the groove. These findings indicate that NP plays a critical role in influenza virus morphology, possibly through its interaction with the M1 layer during virus budding.

Identification of Influenza A/PR/8/34 Donor Viruses Imparting High Hemagglutinin Yields to Candidate Vaccine Viruses in Eggs

“…PR8-B in H5N1 or H2N3 reassortants) mediated the best performance among the HAY 6:2R viruses, such as H7N2, H3N2v and H3N2 viruses, suggesting that functional interactions between HA-NA and PR8 genes are mediated by mutually exclusive elements in the viruses analyzed. This finding is consistent with several earlier studies concluding that functional compatibility between HA-NA (so-called “surface genes”) and PR8 internal genes is an important determinant of antigen yield from reassortant viruses in eggs [12,13,14,15,16,17,42,43]. Taken together, these results indicated that PR8 lineages A (or C) impart the highest hemagglutinin yield for 6:2R virus with low initial antigen yields in eggs.…”

Selective incorporation of vRNP into influenza A virions determined by its specific interaction with M1 protein

“…Previous studies suggest a specific interaction between M1 and vRNP during virus assembly (Gómez-Puertas et al, 2000; Noton et al, 2007; Wu et al, 2011). Our lab also showed that M1-vRNP interaction affects morphology of progeny virions (Bialas et al, 2014). Therefore, we determined if M1 specifically recognizes and interacts with vRNPs to promote specific vRNP incorporation into infectious virions.…”

Nanoparticles decorated with viral antigens are more immunogenic at low surface density

“…We therefore next tested whether similar results would be obtained using smaller NPs, with a diameter (200 nm) similar to that of naturally occurring viruses [11, 25, 26]. We also decided to interrogate the full range of available antigen densities (i.e., very sparse, sparse, moderate and dense; see Figure 1).…”