Figure 3.

Enzymatic and structural analysis of mutations to calcium binding residues. (A) Calcium coordinating residues and their binding states seen at varying calcium concentrations in the different PAD2 structures. (B) Catalytic efficiency (k_cat/K_M) for wild type and calcium-binding mutants. (C) Concentration of calcium required for half-maximal activity (K_0.5) for wild type and calcium-binding mutants. (D) Electron density at the Ca3–5 sites from structures soaked in 10 mM Ca²⁺ (WT, left, PDB: 4N2B; D169A, center, PDB: 4N2G; D177A, right, PDB: 4N2I) where density is contoured at the 5σ level from F_o–F_c omit maps after calcium was removed and simulated annealing was performed during refinement. (E) Percent occupancies of calcium in crystal structures of PAD2 mutants not soaked in CaCl₂ (left column) or soaked in 10 mM CaCl₂ (right column; full list of PDBs in Supporting Information Table S1).