FIG. 3.

Three-dimensional representation of the crystal structure of the RBD of Friend ecotropic murine leukemia virus (Fr-MLV) (5). The crystal structure of the RBD of Fr-MLV (5) was obtained from GenBank (Structure: accession number 1AOL) and visualized with the Cn3D 4.1 program. The RBDs of Fr98 and Fr-MLV are highly homologous except at the variable regions (VRA, VRB, and VRC), and this allowed modeling of the locations of variant Fr98 residues important for neurovirulence in this three-dimensional structure. Virulence-associated residues in VRB are on the upper left part of the molecule, whereas residues 84, 113, 165, and 168 are opposite on the lower right external surface. Because VRA and VRB sequences vary extensively between Fr-MLV and Fr98, it is likely that the details of this portion of the RBD model, such as the two helices and loop structures, are not accurate for Fr98.