Mathias Loesche

Structure of the PTEN Tumor Suppressor Associated with the Fluid Lipid Membranes

e tumor suppressor PTEN1 is a phosphatase involved in the regulation of PI(3,4,5)P3. It consists of a phosphatase and a C2 domain that interact synergistically with anionic lipids in membranes. A single-point mutation of the wild type (wt) protein, H93R, has the same secondary structure but significantly reduced enzyme activity. As for many membrane proteins, the crystal structure of (a truncated) PTEN has been determined2, but the association of the protein with lipid membranes has only been indirectly inferred. We study the association of wt PTEN and H93R with membranes using neutron reflectometry (NR) of tethered bilayer lipid membranes (tBLMs)3,4 which are long-term stable and retain their fluidity with in-plane dynamics similar to that in vesicles.5 Surface Plasmon Resonance (SPR) spectroscopy has also been used to investigate the binding of these two variants of PTEN.Data analysis uses a composition-space model that resolves the thermally disordered membrane with Angstrom resolution,6 enabling us to characterize PTEN association with the bilayer in its physiologically relevant, disordered state. The crystal structure serves as a starting point for model refinement. Computational techniques are used to explore the conformational flexibility of the peptide stretches deleted for crystallization. We observed slight differences in the peripheral association of H93R and wt PTEN with the bilayers headgroup region and speculate how these may be related to their functional distinctions.(1) I. Sansal et al., 2004, J. Clin. Oncology 22:2954.(2) J. Lee,et al., 1999, Cell 99:323.(3) D. J. McGillivray et al., 2007, Biointerphases 2:21.(4) F. Heinrich et al., 2009, Langmuir 25:4219.(5) S. Shenoy et al., 2010, Soft Matter 6, 1263.(6) F. Heinrich et al., J. Appl. Phys., submitted.