Effects of phosphoinositide identity and lateral organization on PTEN binding and structure

PTEN is a phosphatidylinositol phosphate (PIP) phosphatase specific for the 3‐position of the inositol ring. Recent reports have shown that PTEN is activated by PI(4,5)P 2 and that this activation requires a polybasic region located at the N‐terminus of the protein. It was hypothesized that PI(4,5)P 2 aids membrane recruiting and induces a conformational change in PTEN. This study characterizes PTENs binding preferences, investigates its contact points with the lipid bilayer and highlights structural changes upon membrane interaction. Fluorescence quenching experiments involving PC/phosphoinositide vesicles yielded results consistent with an enhanced PTEN binding to PI(4,5)P 2 or PI(5)P containing vesicles, while the interaction with all other phosphoinositide derivatives was only minor. Experiments with a truncated PTEN 16‐403 showed a strongly reduced phosphoinositide affinity and a loss of specificity, while experiments using a peptide representing PTENs N‐terminus (PTEN 1‐21 ) showed preferential PI(4,5)P 2 binding. Infrared spectroscopic measurements furnished results consistent with an increased α‐helical secondary structure content in the presence of PI(4,5)P 2 /PC vesicles, while other phosphoinositides like PI(3,5)P 2 or PI(3,4,5)P 3 did not cause a structural change. Although PS induced a structural change towards more β‐sheet, it did not alter the structural effect of PI(4,5)P 2 .