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Membrane interaction of influenza virus M1 protein
R W Ruigrok1, A Barge, P Durrer
1EMBL Grenoble Outstation, Grenoble Cedex 9, 38042, France. ruigrok@embl-grenoble.fr
Abstract:
The M1 protein of influenza virus is thought to make contact with the cytoplasmic tails of the glycoprotein spikes, lipid molecules in the viral membrane, and the internal ribonucleoprotein particles. Here we show electron micrographs of negatively stained virus particles in which M1 is visualized as a 60-A-long rod that touches the membrane but apparently is not membrane inserted. Photolabeling with a membrane restricted reagent resulted in labeling of the transmembrane region of haemagglutinin but not of M1, also suggesting that most of M1 is not embedded into the hydrophobic core of the viral membrane. Finally, in vitro reconstitution experiments using soluble M1 protein and synthetic liposomes or Madin-Darby canine kidney cell membranes suggest that M1 can bind to negatively charged liposomes and to the cellular membranes and that this binding can be prevented under high-salt conditions. Although none of these experiments prove that there does not exist a minor fraction of M1 that is membrane inserted, it appears that most of M1 in the virus is membrane associated through electrostatic interactions.
Insights
Influenza virus M1 protein primarily associates with the viral membrane via electrostatic interactions, not deep membrane insertion. This finding clarifies the M1 protein's role in viral structure and assembly.
Area of Science:
- Virology
- Structural Biology
- Biochemistry
Background:
- The M1 protein of influenza virus is hypothesized to interact with viral membrane components and internal ribonucleoprotein particles.
- Understanding M1 protein's interaction with the viral membrane is crucial for elucidating influenza virus assembly and structure.
Purpose of the Study:
- To investigate the precise localization and membrane interaction of the influenza virus M1 protein.
- To determine whether M1 protein is embedded within the viral membrane or associated with its surface.
Main Methods:
- Electron microscopy of negatively stained influenza virus particles to visualize M1 protein structure.
- Photolabeling experiments using a membrane-restricted reagent to assess M1 protein's membrane insertion.
- In vitro reconstitution assays with liposomes and cell membranes to study M1 protein binding.
Main Results:
- Electron microscopy revealed M1 protein as a rod-like structure associated with the viral membrane surface, not inserted into it.
- Photolabeling experiments did not label M1 protein, indicating it is not embedded in the hydrophobic core of the membrane.
- In vitro studies showed M1 protein binds to negatively charged liposomes and cell membranes through electrostatic interactions, which are disrupted by high salt concentrations.
Conclusions:
- The majority of influenza virus M1 protein is associated with the viral membrane via electrostatic interactions, rather than being inserted into the lipid bilayer.
- These findings refine our understanding of the M1 protein's role in viral structure and assembly.