FIGURE 6.

The IIA^Man(H10E)-IIB^Man interface and the phosphoryl transition state. A, overall stereoview of the interface, including the modeled His-10′—P—His-175 phosphoryl transition state. B, enlarged view depicting the vicinity around the His-10′—P—His-175 transition state. C, schematic diagram of the phosphoryl transition state. In A and B, the backbones are depicted as ribbons (blue, chain A of IIA^Man; red, chain B of IIA^Man; and green, IIB^Man), and the side-chain atoms are colored according to atom type; carbon, gray; nitrogen, blue; oxygen, red; sulfur, yellow, phosphorus, tan. In C, red dashed lines indicate likely hydrogen bonds with donor acceptor distances < 3.5 Å; blue dashed lines represent potential water-bridged interactions with donor-acceptor distances between 5 and 6 Å. The phosphorus and active site histidines are surrounded by a large number of hydrophobic residues (circled), including the long aliphatic side chains of Arg-172 and Lys-305 of IIB^Man.