Coordination among proteins, lipids and water in membrane fusion and fission probed by solid-state NMR

Abstract

For enveloped viruses such as HIV, influenza, and coronaviruses to enter host cells, the viral and cell envelopes must be fused together. Then, to exit the cell, a new virus particle will pinch off a piece of the host cell membrane. The two membranes must be physically separated to release the virus particle. This process is called “scission” in the context of viral exit and “fission” when simply discussing membrane division.

Viral membrane remodeling proteins catalyze membrane fusion and fission to bring about viral entry and exit from host cells – vital processes in the life cycle of enveloped viruses. The exact mechanism by which membrane remodeling proteins catalyze membrane fusion and fission is not yet fully understood. The membrane remodeling proteins may take any combination of the following actions to facilitate fusion and fission: 1. Directly altering the local curvature of the membrane 2. Altering the line tension at Lo/Ld phase boundaries 3. Forming protein clusters to act collectively on the membrane 4. Altering the local composition of the membrane at the site of fusion or fission 5. Physically disrupting the lipid assemblies, i.e. by inserting protein domains into the membrane and creating membrane defects

In this work, we examine the extent to which HIV’s membrane fusion protein gp41, and Influenza A’s membrane fission protein M2, utilize these five processes to carry out their functions. We use solid-state NMR techniques to probe intermolecular interactions along those lines, with an emphasis on curvature and clustering. The contributions of both proteins and lipids to these processes will be examined. The goal is to better understand the mechanisms of HIV entry and influenza release, which can hopefully guide the development of better therapeutics and vaccines.