FIG. 1.
Location of mutated residues in the three-dimensional structure of gp21. (A) Ribbon diagram of the gp21(338–425) trimer. The coiled-coil-forming helices are colored magenta, the disulfide-bonded loop is green, the C-terminal helices are cyan, and the rest of the chain is grey. The side chains of residues mutated in this study are also shown; the mutated residues in the helix cap region are colored yellow, the mutated residues in the chain reversal region are colored red, and the mutated residues in the C-terminal helix region are colored blue. The atomic radii of Cα atoms of glycine residues have been enlarged for clarity. (B) Close-up view of the helix cap region, colored as in panel A. The side chain of Ser-339 and the first heptad repeat residue, Leu-346, are also shown colored in grey. (C) Superimposition of the N-cap regions of gp21 and HA2. The structures have been superimposed using 45 N-terminal residues in the coiled-coil helices. HA2 is colored cyan (residues 33 to 43 of the N-terminal region of the coiled coil) and blue (residues 171 to 177 of the C-terminal segment), and gp21 residues are colored magenta (residues 338 to 345). The structures are viewed down the threefold axis of the coiled coil. (D) Close-up view of the chain reversal region, colored as in panel A. The side chains of some residues interacting with the mutated residues are also shown colored in grey. (E) Close-up view of the C-terminal helix region, colored as in panel A. The side chains of some residues interacting with the mutated residues are also shown colored in grey. The figure was prepared with the programs BOBSCRIPT (20) and RASTER3D (35).