STRUCTURAL BASIS FOR PHOSPHOPEPTIDE RECOGNITION AND CATALYSIS BY PROTEIN PHOSPHATASES. David Barford, Amit Das, Marie-Pierre Egloff, Laboratory of Molecular Biophysics, University of Oxford, Rex Richards Building OX1 3QU, UK.

Protein phosphatases are signal transduction enzymes that catalyse protein dephosphorylation reactions. In eukaryotic cells, serine, threonine and tyrosine (and to a small extent histidine) residues are subject to reversible phosphorylation by protein kineses and phosphatases. Although protein kinases belong to a single gene family, four gene families encode protein phosphatases, two of which encode protein tyrosine phosphatases (PTPs) while the other two encode serine/threonine specific protein phosphatases. We have determined the structures of representative members of several classes of protein phosphatases including protein tyrosine, phosphatases and Ser/Thr specific protein phosphatases, in some instances in complex with phosphorylated peptides.

The structures of these enzymes will be discussed and the structural information will be used to explain differences in overall structure. The protein tyrosine phosphatases and Ser/Thr protein phosphatases catalyse dephosphorylation reactions by different mechanisms. PTPs utilise thio-phosphate intermediates whereas the Ser/Thr protein phosphatases catalyse single step reactions. The structures of the catalytic sites of protein phosphatases will be discussed in order to undestand the nature of the catalytic mechansims and the basis for substrate specificity. Particular attention will be paid to PTP1B and PP1. The crystal structure of PP1 was solved using multiple wavelength anomalous dispersion methods with tungstate as a heavy atom derivative.