A LIGAND-INDUCED CONFORMATIONAL CHANGE IN THE YERSINIA PROTEIN-TYROSINE-PHOSPHATASE

Protein tyrosine phosphatases (PTPases) play critical roles in the int racellular signal transduction pathways that regulate cell transformat ion, growth, and proliferation. The structures of several different PT Pases have revealed a conserved active site architecture in which a ph osphate-binding loop, together with an invariant arginine, cradle the phosphate of a phosphotyrosine substrate and poise it for nucleophilic attack by an invariant cysteine nucleophile. We previously reported t hat binding of tungstate to the Yop51 PTPase from Yersinia induced a l oop conformational change that moved aspartic acid 356 into the active site, where it can function as a general acid. This is consistent wit h the aspartic acid donating a proton to the tyrosyl leaving group dur ing the initial hydrolysis step. In this report, using a similar struc ture of the inactive Cys 403 --> Ser mutant of the Yersinia PTPase com plexed with sulfate, we detail the structural and functional details o f this conformational change. In response to oxyanion binding, small p erturbations occur in active site residues, especially Arg 409, and tr igger the loop to close. Interestingly, the peptide bond following Asp 356 has flipped to ligate a buried, active site water molecule that a lso hydrogen bonds to the bound sulfate anion and two invariant glutam ines. Loop closure also significantly decreases the solvent accessibil ity of the bound oxyanion and could effectively shield catalytic inter mediates from phosphate accepters other than water. We speculate that the intrinsic loop flexibility of different PTPases may be related to their catalytic rate and may play a role in the wide range of activiti es observed within this enzyme family.