Figure 4

Stereo image of central metal-binding pore. (A) Amino acids lining the metal-binding pore are shown in stick representation. Concentric layers of amino acids are numbered and corresponding polarity indicated by color. Red, blue and yellow indicate negative, positive and neutral charge, respectively. (B) Interaction between upper 3 layers of central pore and hydrated Mg²⁺ ions. Mg²⁺ ions and surrounding water molecules are colored in green and red, respectively. (C) Magnesium coordination binding analysis. An Fo-Fc Mg²⁺ omit map contoured at 5 σ is shown in green mesh. For reference, a 2Fo-Fc map contoured at 1.5 σ (blue mesh) is also shown for Mg²⁺ ions (black sphere) and water molecules (red sphere) in the central pore region. Since the trimmeric structure presented here is generated using three-fold crystallographic symmetry only unique features are indicated. Water molecules bond to Mg²⁺ ions are labeled in red W1 to W4. Distances in Ǻ are indicated in parenthesis with black and purple corresponding to water-metal and water-side chain distances, respectively. Interactions with both metals are indicated as black dashed bonds, while those involving D71 are shown in light purple.