Biophysical Society Thematic Meeting | Ascona, Switzerland

Liposomes, Exosomes, and Virosomes: From Modeling Complex Membrane Processes to Medical Diagnostics and Drug Delivery

Poster Abstracts

31-POS Board 16 PTEN and VSPs: On the Way to Identify the Structural Origin for Their Substrate Specificity Kirstin Hobiger 1 , Michael G. Leitner 1 , Tillmann Utesch 2 , Anja Feuer 1 , Maria Andrea Mroginski 2 , Dominik Oliver 1 , Christian R. Halaszovich 1 . 2 Technische Universität Berlin, Berlin, Germany. 1 Philipps-Universität Marburg, Marburg, Germany, The phosphatase and tensin homolog deleted on chromosome ten (PTEN) is one of the most crucial tumor suppressor proteins in mammals. It counteracts the PI3-kinase signaling cascade by cleaving 3’-site phosphate groups from membranous phosphoinositides (PIs). In doing so, PTEN prevents unlimited cell proliferation and tumor genesis. The phosphatase is a soluble protein that transiently binds to the membrane surface for catalysis. This property hardens the experimental access to PTEN's activity for direct interventions. Voltage-sensitive phosphatases (VSPs) overcome this limitation. The enzymes share high sequential and structural homology to PTEN. However, their enzymatic activity is coupled to the transmembrane potential, which allows a reversible depletion of PIs under experimental control. By substituting the catalytic domain of the VSP from Ciona intestinalis (Ci-VSP) against that one of PTEN, we created a voltage- switchable VSP-chimera with the 3’-site PI-specificity of PTEN. Because VSPs prefer to dephosphorylate the 5’-site position of PI-substrates, we are currently studying native VSPs in comparison to the VSP-chimera to identify the structural origin for the substrate specificity of the phosphatases. For this purpose, we use an approach that combines molecular dynamics simulations and phosphatase activity assays in mammalian cells and in vitro. First experiments revealed the importance of the membrane environment for the regulation of the substrate specificity. In particular, the reaction toward one PI-substrate seems to be controlled by an allosteric mechanism that is mediated by at least one of the flexible loops that surround the active site. Since this regulation process depends on the properties of the membrane used for the phosphatase assay, we are currently searching for the optimal membrane system that will help us to identify the structural determinants for the substrate specificity of PTEN and its homologs.

62