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

• Published in: PLoS biology Vol. 18; no. 9; p. e3000827
• Main Authors: Selzer, Lisa, Su, Zhaoming, Pintilie, Grigore D, Chiu, Wah, Kirkegaard, Karla
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 30.09.2020; Public Library of Science (PLoS)
• Subjects: Amino Acid Sequence; Amino acids; Assembly; Bioengineering; Biology and Life Sciences; Coronaviruses; Cross-Linking Reagents - chemistry; Drug resistance; Electron microscopy; Funding; Genomes; Hydrogen-Ion Concentration; Imaging, Three-Dimensional; Immunology; Influenza; Influenza A; Influenza viruses; Interfaces; Matrix protein; Medicine; Medicine and health sciences; Microscopy; Models, Molecular; Molecular structure; Mutagenesis; Mutation; Mutation - genetics; Oligomers; Orthomyxoviridae; pH effects; Physical Sciences; Physiological aspects; Protein Multimerization; Protein purification; Protein Structure, Secondary; Protein Subunits - chemistry; Proteins; Recombination, Genetic - genetics; Research and Analysis Methods; Ribonucleic acid; RNA; Structural analysis; Structure; Viral Matrix Proteins - chemistry; Viral Matrix Proteins - genetics; Viral proteins; Virion - ultrastructure; Virions; Viruses; United States; United States > US; China; California
• ISSN: 1545-7885; 1544-9173; 1545-7885
• DOI: 10.1371/journal.pbio.3000827

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.