Fig. 14.

Crystal packing of mushroom tyrosinase PPO4 (polyphenol oxidase 4). In the upper left of the figure the Anderson POM [TeW₆O₂₄]⁶⁻ (TEW) is depicted from two perspectives in ball and stick representation (color code: tellurium = brown, tungsten = blue, oxygen = red). On the left the [TeW₆O₂₄]⁶⁻ mediated crosslink of two heterodimers is shown with illustration of the [TeW₆O₂₄]⁶⁻–protein interactions in insets. PPO4 is demonstrated as cartoon with differently colored protein forms and heterodimers (color code: active form of heterodimer 1 = dark cyan, latent form of heterodimer 1 = cyan, active form heterodimer 2 = gold, latent form heterodimer 2 = yellow). Interacting side chains are shown as ball and stick (color code: carbon = dark cyan/cyan/gold/yellow, nitrogen = blue) and water molecules are depicted as small red spheres. On the right of the figure the crystal packing in a 1 × 2 × 1 supercell is illustrated. The proteins are shown in differently colored surface representation and the [TeW₆O₂₄]⁶⁻ anions as red spheres. Every heterodimer is connected to two other dimers, where the linkage on the one side being mediated by two [TeW₆O₂₄]⁶⁻ and on the other site via a protein–protein interaction. This motif is repeated throughout the cell demonstrating the role of [TeW₆O₂₄]⁶⁻ as a form of “glue” between the protein layers.