FIGURE 10.

Strength of the mutational effects of seven residues in Tyr¹²²-hydrophobic cluster on E2P hydrolysis and lumenal Ca²⁺ affinity. The detailed structure at Y122-HC is shown with (the analog for E2∼P, the transition state of the E2P hydrolysis (21), PDB code: 1XP5 (15)). The seven residues involved in Y122-HC (Tyr¹²²/Leu¹¹⁹, Ile¹⁷⁹/Leu¹⁸⁰, Ile²³², and Val⁷⁰⁵/Val⁷²⁶), bound at the phosphorylation site Asp³⁵¹, and the bound potassium ion are shown by van der Waals spheres. The seven residues in Y122-HC are colored differently based on the strength of the retardation of the E2P hydrolysis rate (lower panel) and that of the increase in the lumenal Ca²⁺ affinity (upper panel). The color changes gradually from red for the strongest effects to blue for weakening.