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Mutations in the membrane-proximal region of the influenza A virus M2 protein cytoplasmic tail have modest effects on virus replication.

ABSTRACT: Influenza A virus encodes M2, a proton channel that has been shown to be important during virus entry and assembly. In order to systematically investigate the role of the membrane-proximal residues in the M2 cytoplasmic tail in virus replication, we utilized scanning and directed alanine mutagenesis in combination with transcomplementation assays and recombinant viruses. The membrane-proximal residues 46 to 69 tolerated numerous mutations, with little, if any, effect on virus replication, suggesting that protein structure rather than individual amino acid identity in this region may be critical for M2 protein function.

SUBMITTER: Stewart SM

PROVIDER: S-EPMC3209349 | biostudies-literature | 2011 Dec

REPOSITORIES: biostudies-literature

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Mutations in the membrane-proximal region of the influenza A virus M2 protein cytoplasmic tail have modest effects on virus replication.

Stewart Shaun M SM Pekosz Andrew A

Journal of virology 20110914 23

Influenza A virus encodes M2, a proton channel that has been shown to be important during virus entry and assembly. In order to systematically investigate the role of the membrane-proximal residues in the M2 cytoplasmic tail in virus replication, we utilized scanning and directed alanine mutagenesis in combination with transcomplementation assays and recombinant viruses. The membrane-proximal residues 46 to 69 tolerated numerous mutations, with little, if any, effect on virus replication, sugges ...[more]

PMID: 21917980

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Project description:The influenza A virus M1 and M2 proteins play important roles in virus assembly and in the morphology of virus particles. Mutations in the distal cytoplasmic tail region of M2, and in particular a tyrosine-to-alanine mutation at residue 76 (Y76A), were essential for infectious virus production and filament formation while having limited effects on total virus particle budding. Using a novel selection method, mutations at seven different M1 amino acids (residue 73, 94, 135, 136, or 138 or a double mutation, 93/244) that are not found in circulating influenza virus strains or have not been previously identified to play a role in influenza A virus assembly were found to complement the lethal M2Y76A mutation. These M1 suppressor mutations restored infectious virus production in the presence of M2Y76A and mediated increased budding and filament formation even in the absence of M2. However, the efficiency of infectious virus replication was still dependent on the presence of the distal region of the M2 cytoplasmic tail. The data suggest that influenza A virus budding and genome incorporation can occur independently and provide further support for complementary roles of the M1 and M2 proteins in virus assembly.IMPORTANCE Influenza virus particle assembly involves the careful coordination of various viral and host factors to optimally produce infectious virus particles. We have previously identified a mutation at position 76 of the influenza A virus M2 protein that drastically reduces infectious virus production and filament formation with minimal effects on virus budding. In this work, we identified suppressor mutations in the M1 protein which complement this lethal M2 mutation by increasing the efficiency with which virus particles bud from infected cells and restoring filament formation at the infected-cell surface. M2 distal cytoplasmic domain sequences were still required for optimal infectivity. This indicates that M1 and M2 can functionally replace each other in some, but not all, aspects of virus particle assembly.

Project description:The influenza A M2 protein forms a proton channel for virus infection and also mediates virus assembly and budding. The minimum protein length that encodes both functions contains the transmembrane (TM) domain (roughly residues 22-46) for the amantadine-sensitive proton-channel activity and an amphipathic cytoplasmic helix (roughly residues 45-62) for curvature induction and virus budding. However, structural studies involving the TM domain with or without the amphipathic helix differed on the drug-binding site. Here we use solid-state NMR spectroscopy to determine the amantadine binding site in the cytoplasmic-helix-containing M2(21-61). (13)C-(2)H distance measurements of (13)C-labeled protein and (2)H-labeled amantadine showed that in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayers, the first equivalent of drug bound S31 inside the M2(21-61) pore, similar to the behavior of M2 transmembrane peptide (M2TM) in DMPC bilayers. The nonspecific surface site of D44 observed in M2TM is disfavored in the longer peptide. Thus, the pharmacologically relevant drug-binding site in the fully functional M2(21-61) is S31 in the TM pore. Interestingly, when M2(21-61) was reconstituted into a virus-mimetic membrane containing 30% cholesterol, no chemical shift perturbation was observed for pore-lining residues, whereas M2TM in the same membrane exhibited drug-induced chemical shift changes. Reduction of the cholesterol level and the use of unsaturated phospholipids shifted the conformational equilibrium of M2TM fully to the bound state but did not rescue drug binding to M2(21-61). These results suggest that the amphipathic helix, together with cholesterol, modulates the ability of the TM helix to bind amantadine. Thus, the M2 protein interacts with the lipid membrane and small-molecule inhibitors in a complex fashion, and a careful examination of the environmental dependence of the protein conformation is required to fully understand the structure-function relation of this protein.

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Mutations in the membrane-proximal region of the influenza A virus M2 protein cytoplasmic tail have modest effects on virus replication.

Publications

Mutations in the membrane-proximal region of the influenza A virus M2 protein cytoplasmic tail have modest effects on virus replication.

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