Positive density at the primary site in Apo-K62W. (A) Electron density at the primary site with no ligands modeled for Apo-K62W (top) or PIP₂-bound K62W (bottom). Only fo-fc electron density calculated at 2.8-Å resolution and contoured at 2.5σ (green) is shown for clarity. The dashed boxes indicate the space corresponding to electron densities shown in B. Blue indicates nitrogen atoms. (B) Electron density recalculated after refinement in the presence of putative ligands, PI(4,5)P₂, PI(4)P₁, or PI(5)P₁ (shown as sticks). The solid box indicates the correct assignment. 2fo-fc electron density at 2.8-Å resolution for Apo-K62W and PIP₂-bound K62W, respectively, contoured at 1σ, is shown in gray. fo-fc electron density at 2.8-Å resolution contoured at 3σ and −3σ is shown in green and red, respectively. Orange indicates phosphate atoms.