Electron microscopy of the human respiratory syncytial virus fusion protein and complexes that it forms with monoclonal antibodies

Full-length fusion (F) glycoprotein of human respiratory syncytial virus (H RSV) and a truncated anchorless mutant lacking the C-terminal 50 amino acid s 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. , rosetres) 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 tw o forms of F protein may represent different structures that the molecule m ay adopt before and after activation for its role in membrane fusion. Studi es of complexes of these structures with monoclonal antibodies of known spe cificity provide information on the three-dimensional organization of antig enic sites on the F protein and confirm the oligomeric structure, possibly trimeric, of both full-length F and membrane anchorless F. (C) 2000 Academi c Press.