FIG. 7.

(A) Comparison of the proposed structure of the BLV RBD with a known structure (20) of the F-MuLV RBD monomer. Structures are depicted by using RasMol, version 2.7.1.1 (4, 57). Yellow, β strands; magenta, helices. Of the β strands predicted to be present in the BLV RBD, 1β, 2β, 4β, 8β, and 9β were modeled as such; 3β, 5β, and 7β were modeled as β-like structures, and 6β was not modeled. Of the predicted α helices, Aα, Dα, and Iα were modeled, whereas Eα and Gα were not. The BLV RBD has no helix analogous to Cα of F-MuLV. Coordinates for the BLV model and an annotated version of Fig. 7 are available from the corresponding author upon request. (B) Space-filling models of the BLV RBD illustrating the locations of the variant residues described in this paper (yellow) and the strain-specific Y108H of Bat₂cl₆ BLV (dark blue), as well as locations of peptides whose polyclonal antibodies neutralize infectivity or block fusion (10, 49). Pink, aa 72 to 81 and 111 to 125; light green, aa 97 to 106; light blue, aa 131 to 150. (C) Locations of strain-specific variant amino acids (A48T, A73P, K74R, S82F, Y108H, and R111H; dark blue) and amino acids varying in individual BLV isolates (S39F, S56F, S58A, D60N, Q95K, V140A, N141D, I144T, and H148Q; dark green) among complete BLV Env RBD sequences in the GenBank database. BLV Env sequences from K02120 (55) and M35242 (39) are the same as the those for the Bat₂cl₆ strain except for Y108. Accession numbers of BLV sequences encoding the depicted variants are K02251 (53); M35238, M35239, and M35240 (39); D00647 (13); S83530 (40); AF111171 (51); AF257515 (17); and AF067081.