Thesis advisor: Mary F. Roberts / Inositol-containing molecules and inositol phosphatases have diverse roles in cells. One of the inositol phospholipids phosphatases, PTEN (Phosphatase and Tensin Homolog deleted on Chromosome Ten), is a tumor suppressor and antagonizes the PI3K signaling pathway by dephosphorylating PI(3,4,5)P3 at the 3 position of the inositol ring. In testing predictions of a molecular dynamics simulation, a hydrophobic site adjacent to the active site on PTEN was identified and verified by protein kinetic studies. This hydrophobic site plays an important role in substrate and substrate analogue binding with one of residues, Arg47, critical for PTEN phosphatase activity. Mutations of Arg47 reduced enzyme activities toward both the short-chain substrate as monomers and micelles and long-chain phospholipid presented in vesicles. PI(4,5)P2 the product of PI(3,4,5)P3 dephosphorylation, activates PTEN. Studies by others suggested this occurred when the product was bound to the N-terminal region of the protein (not visible in the crystal structure). However, no direct proof of this existed. The effect of PI(4,5)P2 on PTEN enzyme activities in different substrates systems was studied. 31P NMR was used to probe the spatial location and functional role of PI(4,5)P2 binding site. The fixed field 31P NMR and high resolution field cycling 31P NMR results indicated there are discrete sites for both substrate and activator lipids on PTEN, and both of sites are spatially separate from the hydrophobic site. The active site, adjacent hydrophobic site, and N-terminal activator binding site worked synergistically to regulate PTEN interacting with the membrane. Thermophilic and hyperthermophilic archaea and bacteria thrive at high temperatures. They often accumulate small organic molecules, called compatible solutes or osmolytes, to protect proteins from thermal denaturation. The thermoprotection mechanism of compatible solutes was explored using inositol monophosphatase (IMPase) from Archaeoglobus fulgidus as the model protein. The protective effect of unusual compatible solutes, di-inositol-1,1'-phosphate (DIP) and diglycerol phosphate (DGP), as well as common compatible solutes glutamate and other anions, on the IMPase thermostability was studied. Specific binding sites of glutamate ions on the IMPase were identified by crystallography and field cycling NMR. However, mutations at these discrete binding sites did not eliminate the thermoprotection, but reduced the thermal stability (Tm) of the protein. Our results indicate the specific binding of osmolytes to the protein exists, but they do not account for the thermoprotection. / Thesis (PhD) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.
| Identifer | oai:union.ndltd.org:BOSTON/oai:dlib.bc.edu:bc-ir_101374 |
| Date | January 2013 |
| Creators | Wei, Yang |
| Publisher | Boston College |
| Source Sets | Boston College |
| Language | English |
| Detected Language | English |
| Type | Text, thesis |
| Format | electronic, application/pdf |
| Rights | Copyright is held by the author, with all rights reserved, unless otherwise noted. |
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