Structure of a lipid-bound viral membrane assembly protein reveals a modality for enclosing the lipid bilayer

Significance Cellular membranes are maintained as closed structures in the cytosol, and any breaches in membranes during reorganization are transient. However, open-ended membranes, likely derived from the endoplasmic reticulum, persist in vaccinia virus-infected cells during the assembly of the vaccinia envelope. A group of viral proteins have been identified to be required for this process, providing a unique opportunity for dissecting the molecular mechanism of membrane scission and remodeling. Our structural and functional studies of one of these viral proteins reveal a cage-like soluble protein that traps internally multiple lipids with a bilayer-like configuration. Our studies reveal a protein modality for enclosing the lipid bilayer and suggest a mechanism for stabilizing the open-ended membrane sheets.