Phospholipid binding sites of PTEN: Exploring the mechanism of PIP2 activation [Enzymology]

November 27th, 2014 by Wei, Y., Stec, B., Redfield, A. G., Weerapana, E., Roberts, M. F.

The lipid phosphatase activity of the tumor suppressor PTEN is enhanced by the presence of its biological product, phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2). This enhance-ment is suggested to occur via the product binding to the N-terminal region of the protein. PTEN effects on short-chain phosphoinositide 31P linewidths and on the full field dependence of the spin-lattice relaxation rate (measured by high resolution field cycling 31P NMR using spin-labeled protein) are combined with enzyme kinetics with the same short-chain phospholipids to characterize where PI(4,5)P2 binds on the protein. The results are used to model a discrete site for a PI(4,5)P2 molecule close to, but distinct from, the active site of PTEN. This PI(4,5)P2 site uses Arg47 and Lys13 as phosphate ligands, explaining why PTEN R47G and K13E can no longer be activated by that phosphoinositide. Placing a PI(4,5)P2 near the substrate site allows for proper orientation of the enzyme on interfaces and should facilitate processive catalysis.