Role of influenza virus M1 protein in the viral budding process

Abstract

The initial step in the influenza virus budding process involves most likely the organisation of the glycoproteins in semi-crystalline membrane structures called “rafts”. M1 protein then binds to the lipids and the cytoplasmic tails in these rafts (work by Kai Simons, Bob Lamb and Debi Nayak). In a next step, ribonucleoproteins (RNPs) bind to this initial scaffold. Here, we will discuss biochemical and structural data on M1 protein and its interactions with synthetic liposomes and viral RNPs. In solution, intact M1 is a monomeric, elongated protein. A recent neutral pH crystal structure of the N-terminal domain confirms the monomeric nature of M1 in solution. M1 seems to interact with negatively charged membranes though its N-terminal domain. This interaction has an important electrostatic component. The C-terminal domain binds to the RNPs in vitro. In relation to our work on the Ebola virus VP40 matrix protein, we suggest that there might be two conformations of M1 in the infected cell: one that is soluble and has a low affinity for membranes and RNP and one that polymerises easily and that has a high affinity for membranes and RNPs.