The Cytoplasmic Tail of the Influenza A Virus M2 Protein Plays a Role in Viral Assembly

Abstract

The viral replication cycle concludes with the assembly of viral components to form progeny virions. For influenza A viruses, the matrix M1 protein and two membrane integral glycoproteins, hemagglutinin and neuraminidase, function cooperatively in this process. Here, we asked whether another membrane protein, the M2 protein, plays a role in virus assembly. The M2 protein, comprising 97 amino acids, possesses the longest cytoplasmic tail (54 residues) of the three transmembrane proteins of influenza A viruses. We therefore generated a series of deletion mutants of the M2 cytoplasmic tail by reverse genetics. We found that mutants in which more than 22 amino acids were deleted from the carboxyl terminus of the M2 tail were viable but grew less efficiently than did the wild-type virus. An analysis of the virions suggested that viruses with M2 tail deletions of more than 22 carboxy-terminal residues apparently contained less viral ribonucleoprotein complex than did the wild-type virus. These M2 tail mutants also differ from the wild-type virus in their morphology: while the wild-type virus is spherical, some of the mutants were filamentous. Alanine-scanning experiments further indicated that amino acids at positions 74 to 79 of the M2 tail play a role in virion morphogenesis and affect viral infectivity. We conclude that the M2 cytoplasmic domain of influenza A viruses plays an important role in viral assembly and morphogenesis.

The Influenza Matrix Protein 2 as a Vaccine Target

“…In particular, virus particles generated by infection with a 28-aa deletion mutant virus contained reduced amounts of packaged genome segments [30]. Iwatsuki-Horimoto et al confirmed these findings and, in addition, demonstrated that virions obtained from M2 tail truncated mutant viruses often displayed a filamentous morphology, whereas wild-type virions were spherical [31]. An interaction of the cytoplasmic tail of M2 with M1 and perhaps the genomic ribonucleoprotein complexes may be essential for proper Influenza A virion formation and budding.…”

Improvement of H5N1 influenza vaccine viruses: Influence of internal gene segments of avian and human origin on production and hemagglutinin content

“…To this purpose a set of H5N1-PR8 reassortant influenza viruses with M or PB1 segments derived from avian or human strains were generated and investigated regarding replication in embryonated chicken eggs and HA content. We chose this strategy as the viral M1 protein interacts with surface glycoproteins and contributes to virus assembly [22], whereas the cytoplasmic tail of the M2 protein is required for efficient genome packaging [24] and also contributes to virus assembly [35]. The PB1 gene was included as it was inherited in some circumstances from a seasonal WT isolate or the pandemic H1N1-2009 virus to the corresponding vaccine strains during classical reassortment.…”

Detection of Proton Movement Directly across Viral Membranes To Identify Novel Influenza Virus M2 Inhibitors

“…Activation of M2 is triggered by low pH in host cell endosomes, resulting in an influx of protons into the virus and acidification that releases the viral RNA into the host cell (2)(3)(4). M2 also helps to package viral RNA (5,6) and regulate pH in the Golgi apparatus of infected cells during viral assembly (7). Two FDA-approved adamantane-based drugs, amantadine and rimantadine (2,8), are potent M2 inhibitors that can neutralize influenza virus in humans and other animals.…”