Figure 4.

Crystal packing in the K33S crystals. (a) The crystal lattice contains stacked layers of protein molecules. The A and B chains are colored yellow and blue, respectively; the Ser33 residues are shown as red spheres, emphasizing their positioning at the junction between adjacent layers in the lattice. The outline of the triclinic unit cell is shown. (b) An orthogonal view of the lattice packing, showing a single layer. The larger and smaller interfaces are shown as green and red dashed lines. (c, d) Detailed views showing neighboring basic residues in the environment of the Ser33 side chain in the A chain (c) and B chain (d); a lysine residue at position 33 would cause electrostatic repulsion in each case.