Pseudotype and chimeric viruses

The M2 protein of influenza A viruses is a small, tetrameric transmembrane protein which plays a role in virus entry and egress. The proton channel activity of the M2 protein plays a role in virus uncoating and may help to preserve the metastable conformation of the HA of some IAV strains. In addition, the proton channel activity may disturb cellular ion homeostasis and may trigger inflammation. The amphipathic helix which is C-terminal of the transmembrane domain, is believed to induce membrane curvature in a cholesterol-dependent manner and to mediate membrane scission at the end of the budding process. The long cytoplasmic tail has been shown to interact with viral M1 protein as well multiple cellular proteins including the autophagy protein microtubule-associated protein 1 light chain 3 (LC3). A highly conserved LC3-interacting region (LIR) is responsible for recruitment of LC3 to the IAV budding site. In this project we are addressing the question whether the interaction of M2 with LC3 is important for virus formation and release. To this end, we generated virus mutants based on two different H1N1 viruses, one strain forming filamentous particles, while the other forms spherical virions. Our preliminary results confirmed the previous observation that mutation of the LIR motif prevents translocation of LC3 to the plasma membrane. While M2 ion channel activity, virus stability, or recruitment of M1 protein to the plasma membrane were not affected by the mutant LIR motif, formation of filamentous virions was abrogated and release of infectious virus significantly reduced. Further analysis of LIR mutant viruses will help to further decipher the process of IAV egress and may lead to the identification of new targets for antiviral therapies.

The recently identified bat IAV H17N10 and H18N11 encode M2 proteins, which show only low sequence homology to the highly conserved M2 proteins of (“classical”) IAV. The goal of this project was to characterize these unusual M2 proteins further. We observed that the M2 proteins of bat IAV did not fully protect the acid-sensitive HA of an avian IAV strain from low pH-induced conformational change indicating low proton channel activity (Thompson et al., 2023). This unusual feature may help to avoid M2-mediated cytotoxic effects and inflammation in bats infected with H17N10 or H18N11. In contrast to classical M2 proteins, the N31S substitution caused a dramatic increased protection of acid-sensitive HA conformation by bat IAV M2 proteins. This remarkable gain of function may help to understand how single point mutations can modulate proton channel activity. In addition, the cytoplasmic domain was found to be responsible for the low cell surface expression level of bat IAV M2 proteins. Given that the M2 cytoplasmic domain of conventional IAV is well known to participate in virus assembly at the plasma membrane, this atypical feature might have consequences for bat IAV budding and egress. In present studies, we attempt to identify cellular proteins that bind to the M2 cytoplasmic domain and assist in these processes.


  • SNSF Project no. 310030_189151


  • Martin Schwemmle, Institute of Virology, University of Freiburg, Germany
  • Jean-Sebastien Rougier, Institute of Biochemistry and Molecular Medicine, University of Bern, Switzerland