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)P₂ and that this activation requires a polybasic region located at the N-terminus of the protein. It was hypothesized that PI(4,5)P₂ 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)P₂ 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)P₂ binding. Infrared spectroscopic measurements furnished results consistent with an increased α-helical secondary structure content in the presence of PI(4,5)P₂/PC vesicles, while other phosphoinositides like PI(3,5)P₂ or PI(3,4,5)P3 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)P₂. [ABSTRACT FROM AUTHOR]