FIGURE 9.

Ribbon diagrams of the model of diC₆PI(4,5)P₂ binding to PTEN at a discrete site near the active site are compatible with the ³¹P electron distances to the Cys-124 spin label. A, view of the phosphatase domain as seen from the membrane. The sulfur of Cys-124 is the yellow sphere to which the 2,2,5,5-tetramethyl-1-oxyl-3-methyl methanethiosulfonate is attached. The PI(4,5)P₂ molecule, placed according to the surface features and to the relative distances determined by NMR, forms hydrogen-bonded contacts with Arg-47 and Lys-13, both critical residues for the PIP₂ activation to be observed. B, surface representation of the phosphatase domain, in a similar view to that in A, colored by the electrostatic potential (red, negative, and blue, positive) with both substrate and activator docked to their sites. The PI(3,4,5)P₃ molecule (magenta) is docked at the active site marked by the dark loop and the yellow sphere depicting Cys-124. The PI(4,5)P₂ molecule (in cyan) occupies the same site as in A. The N-terminal helix is docked into the phosphatase domain, and its positive electrostatic potential complements the charges of the domain to create a positive membrane binding profile.