Crystal structure of the MAPK phosphatase Pyst1 catalytic domain and implications for regulated activation

The crystal structure of the catalytic domain from the MAPK phosphatase Pys t1 (Pyst1-CD) has been determined at 2.35 Angstrom. The structure adopts a protein tyrosine phosphatase (PTPase) fold with a shallow active site that displays a distorted geometry in the absence of its substrate with some sim ilarity to the dual-specificity phosphatase cdc25, Functional characterizat ion of Pyst1-CD indicates it is sufficient to dephosphorylate activated ERK 2 in vitro, Kinetic analysis of Pyst1 and Pyst1-CD using the substrate p-ni trophenyl phosphate (pNPP) reveals that both molecules undergo catalytic ac tivation in the presence of recombinant inactive ERK2, switching from a low - to high-activity form, Mutation of Asp 262, located 5.5 Angstrom distal t o the active site, demonstrates it is essential for catalysis in the high-a ctivity ERK2-dependent conformation of Pyst1 but not for the low-activity E RK2-independent form, suggesting that ERK2 induces closure of the Asp 262 l oop over the active site, thereby enhancing Pyst1 catalytic efficiency.