Electron Microscopy of the Human Respiratory Syncytial Virus Fusion Protein and Complexes That It Forms with Monoclonal Antibodies

Abstract

Full-length fusion (F) glycoprotein of human respiratory syncytial virus (HRSV) and a truncated anchorless mutant lacking the C-terminal 50 amino acids were expressed from vaccinia recombinants and purified by immunoaffinity chromatography and sucrose gradient centrifugation. Electron microscopy of full-length F protein in the absence of detergents revealed micelles, (i.e., rosettes) containing two distinct types of protein rods, one cone-shaped and the other lollipop-shaped. Analysis of membrane anchorless F molecules indicated that they were similar to the cone-shaped rods and that rosettes, which they formed on storage, were made up of lollipop-shaped rods. The two forms of F protein may represent different structures that the molecule may adopt before and after activation for its role in membrane fusion. Studies of complexes of these structures with monoclonal antibodies of known specificity provide information on the three-dimensional organization of antigenic sites on the F protein and confirm the oligomeric structure, possibly trimeric, of both full-length F and membrane anchorless F.