Structure and function studies of protein tyrosine phosphatases
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Protein phosphorylation is one of the post-translational modifications of proteins and regulates nearly every aspect of cell life. In mamallian cells, most of the protein phosphorylations occur on Ser, Thr and Tyr residues. Among them, the phosphorylation on Tyr residues is controlled by the concerted actions of protein tyrosine kinases and protein-tyrosine phosphatases (PTPs). The PTPs consist of a superfamily of enzymes which have diverse functions. Understanding the structural properties of these PTPs and characterizing the structure and function relationship of PTPs will provide insight into how these important signaling molecules function in cells.;In the first part of the thesis, we explored the structural basis of selective PTP inhibition, solved the complex structure of YopH in complex of pNCS and the complex structure of PTP1B with the bidentate inhibitor. Combined with muatagenesis and kinetic studies, we identified specific interactions of YopH with pNCS involving an important second layer Arg residue in the active site, which contributes to the pNCS selectivity. Other than the active site, the complex structure of the bidentate inhibitor with PTP1B discloses a second site, which contributes to the selectivity of PTP1B for the inhibitor. The studies provide good examples that specific PTP inhibitors can be achieved by targeting to either the second layer residues of the active site or the residues of a peripheral site.;In the second part of the thesis, we solved crystal structures of PRL-1. The structures revealed trimer formation of the protein in the crystal, a disulfide bond under oxidizing conditions, and a C-terminal basic region involved in membrane binding. Next I tested the contributions of these specific structural features to PRL-1 functions. The results suggest that trimer formation is a possible regulatory mechanism for PRL-1. Further by systematic mutation of C-terminal basic charged residues, we found that the C-terminal basic charged region is a determinant of PRL-1 subcellular localization. All these results provide solid evidences of contribution of specific structure properties of PRL-1 to its functions.
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