Figure 2. The three β4-β4 dimerization interfaces found in ME ICA512 crystals.

Panel A, crystals grown at pH 7.5 or 8.5 and 0.2 mM Ca²⁺. Panels B and C, β4 interfaces formed in the tetrameric asymmetric unit of crystals grown at pH 4.5. To simplify the view, only some of the residues have been numbered. The main-chain, hydrogen-bond bridges are displaced by one and two steps in panels B and C, respectively, compared with Panel A. Side chains involved in hydrogen bonds across the interface are shown.