phosphorus-radioisotopes and Hamartoma-Syndrome--Multiple

PTEN exerts its tumour suppressor function by dephosphorylating the phospholipid second messenger phosphatidylinositol-3,4,5-trisphosphate (PIP(3)). Herein, we demonstrate that the PTEN-catalysed PIP(3) dephosphorylation reaction involves two-steps: (i) formation of a phosphoenzyme intermediate (PE) in which Cys-124 in the active site is thiophosphorylated, and (ii) hydrolysis of PE. For protein tyrosine- and dual-specificity phosphatases, catalysis requires the participation of a conserved active site aspartate as the general acid in Step 1. Its mutation to alanine severely limits PE formation. However, mutation of the homologous Asp-92 in PTEN does not significantly limit PE formation, indicating that Asp-92 does not act as the general acid. G129E is a common germline PTEN mutations found in Cowden syndrome patients. Mechanistic analysis reveals that this mutation inactivates PTEN by both significantly slowing down Step 1 and abolishing the ability to catalyse Step 2. Taken together, our results highlight the mechanistic similarities and differences between PTEN and the conventional protein phosphatases and reveal how a disease-associated mutation inactivates PTEN.

Topics: Animals; Aspartic Acid; Binding Sites; Catalysis; Conserved Sequence; Cysteine; Glycine; Hamartoma Syndrome, Multiple; Humans; Hydrogen-Ion Concentration; Hydrolysis; Kinetics; Models, Biological; Mutation; Phosphatidylethanolamines; Phosphatidylinositol Phosphates; Phospholipids; Phosphoprotein Phosphatases; Phosphorus Radioisotopes; Phosphorylation; PTEN Phosphohydrolase; Rats; Time Factors