Full-length three-dimensional structure of the influenza A virus M1 protein and its organization into a matrix layer

PLoS Biol. 2020 Sep 30;18(9):e3000827. doi: 10.1371/journal.pbio.3000827. eCollection 2020 Sep.

Abstract

Matrix proteins are encoded by many enveloped viruses, including influenza viruses, herpes viruses, and coronaviruses. Underneath the viral envelope of influenza virus, matrix protein 1 (M1) forms an oligomeric layer critical for particle stability and pH-dependent RNA genome release. However, high-resolution structures of full-length monomeric M1 and the matrix layer have not been available, impeding antiviral targeting and understanding of the pH-dependent transitions involved in cell entry. Here, purification and extensive mutagenesis revealed protein-protein interfaces required for the formation of multilayered helical M1 oligomers similar to those observed in virions exposed to the low pH of cell entry. However, single-layered helical oligomers with biochemical and ultrastructural similarity to those found in infectious virions before cell entry were observed upon mutation of a single amino acid. The highly ordered structure of the single-layered oligomers and their likeness to the matrix layer of intact virions prompted structural analysis by cryo-electron microscopy (cryo-EM). The resulting 3.4-Å-resolution structure revealed the molecular details of M1 folding and its organization within the single-shelled matrix. The solution of the full-length M1 structure, the identification of critical assembly interfaces, and the development of M1 assembly assays with purified proteins are crucial advances for antiviral targeting of influenza viruses.

Publication types

  • Research Support, American Recovery and Reinvestment Act
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cross-Linking Reagents / chemistry
  • Hydrogen-Ion Concentration
  • Imaging, Three-Dimensional*
  • Models, Molecular
  • Mutation / genetics
  • Protein Multimerization
  • Protein Structure, Secondary
  • Protein Subunits / chemistry
  • Recombination, Genetic / genetics
  • Viral Matrix Proteins / chemistry*
  • Viral Matrix Proteins / genetics
  • Virion / ultrastructure

Substances

  • Cross-Linking Reagents
  • M1 protein, Influenza A virus
  • Protein Subunits
  • Viral Matrix Proteins