[Source: PLoS ONE, full text: (LINK). Abstract, edited.]
Specific Residues in the 2009 H1N1 Swine-Origin Influenza Matrix Protein Influence Virion Morphology and Efficiency of Viral Spread In Vitro
Kristy M. Bialas, Emily A. Desmet¤, Toru Takimoto*
Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York, United States of America
In April 2009, a novel influenza virus emerged as a result of genetic reassortment between two pre-existing swine strains. This highly contagious H1N1 recombinant (pH1N1) contains the same genomic background as North American triple reassortant (TR) viruses except for the NA and M segments which were acquired from the Eurasian swine lineage. Yet, despite their high degree of genetic similarity, we found the morphology of virions produced by the pH1N1 isolate, A/California/04/09 (ACal-04/09), to be predominantly spherical by immunufluorescence and electron microscopy analysis in human lung and swine kidney epithelial cells, whereas TR strains were observed to be mostly filamentous. In addition, nine clinical pH1N1 samples collected from nasal swab specimens showed similar spherical morphology as the ACal-04/09 strain. Sequence analysis between TR and pH1N1 viruses revealed four amino acid differences in the viral matrix protein (M1), a known determinant of influenza morphology, at positions 30, 142, 207, and 209. To test the role of these amino acids in virus morphology, we rescued mutant pH1N1 viruses in which each of the four M1 residues were replaced with the corresponding TR residue. pH1N1 containing substitutions at positions 30, 207 and 209 exhibited a switch to filamentous morphology, indicating a role for these residues in virion morphology. Substitutions at these residues resulted in lower viral titers, reduced growth kinetics, and small plaque phenotypes compared to wild-type, suggesting a correlation between influenza morphology and efficient cell-to-cell spread in vitro. Furthermore, we observed efficient virus-like particle production from cells expressing wild-type pH1N1 M1, but not M1 containing substitutions at positions 30, 207, and 209, or M1 from other strains. These data suggest a direct role for pH1N1 specific M1 residues in the production and release of spherical progeny, which may contribute to the rapid spread of the pandemic virus.
Citation: Bialas KM, Desmet EA, Takimoto T (2012) Specific Residues in the 2009 H1N1 Swine-Origin Influenza Matrix Protein Influence Virion Morphology and Efficiency of Viral Spread In Vitro. PLoS ONE 7(11): e50595. doi:10.1371/journal.pone.0050595
Editor: Yi Guan, The University of Hong Kong, China
Received: August 30, 2012; Accepted: October 24, 2012; Published: November 27, 2012
Copyright: © 2012 Bialas et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was supported by National Institutes of Health (NIH) R21-A1078130 and the New York Influenza Center of Excellence (NYICE), a member of the NIAID CEIRS network, under NIH contract HHSN266200700008C. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
* E-mail: firstname.lastname@example.org
¤Current address: Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, New York, United States of America