FIG. 4.

Key interfaces formed by 3CD-3CD interactions. (a) The three labeled interfaces are formed between symmetry-related molecules of 3CD. Interfaces D-C and D-C′ are each formed between the 3C domain of one molecule and the 3D domain of another. Interface D-D is formed between two 3D domains that are related by twofold crystallographic symmetry. Green, yellow, and blue ribbons come from three different 3CD molecules. The thumb, palm, and fingers region of the green molecule are labeled. The N terminus of the yellow 3C domain is indicated. (b) Interface D-C is shown in stereo. Key residues and hydrogen bonds are indicated. (c) A portion of interface D-D is shown in stereo, with some key residues and hydrogen bonds indicated. Two symmetry-related copies of the putative Zn²⁺ coordination site are present, with Zn²⁺ ions indicated as gray spheres. Pro88 from interface D-C is included in both panel b and panel c as an aid to orientation.