Figure 4.

Stereoview of heme groups (brown) and the intervening protein and solvent medium. Residues below (a) and above (b) the heme plane on the left-hand side are shown separately. The side- and main-chain atoms of 14 residues on each molecule participate in the interface, burying 400 Ų of solvent-accessible surface area on Mol_i (green) and 360 Ų on Mol_i+1 (gray). Close contacts (black traces) in the interface include those between Ile-81_i and Ile-75_i+1, and the heme vinyl_i and Lys-55_i+1. The side chain of Lys-55_i+1 and the peptide carbonyl of Ile-81_i form the only direct protein–protein hydrogen bond (yellow traces). Water-bridged hydrogen bonds link the main chain of Phe-82_i to that of Lys-73_i+1, the side chain of Asp-16_i to that of Lys-55_i+1, and the main chain of Ile-81_i to both the main and side chains of Lys-55_i+1. A series of two or more water molecules (blue spheres) mediate additional hydrogen bonds between interfacial residues.