THE X-RAY CRYSTAL-STRUCTURES OF YERSINIA TYROSINE PHOSPHATASE WITH BOUND TUNGSTATE AND NITRATE - MECHANISTIC IMPLICATIONS

X-ray crystal structures of the Yersinia tyrosine phosphatase (PTPase) in complex with tungstate and nitrate have been solved to 2.4-Angstro m resolution, Tetrahedral tungstate, WO42-, is a competitive inhibitor of the enzyme and is isosteric with the substrate and product of the catalyzed reaction, Planar nitrate, NO3-, is isosteric with the PO3 mo iety of a phosphotransfer transition state, The crystal structures of the Yersinia PTPase with and without ligands, together with biochemica l data, permit modeling of key steps along the reaction pathway, These energy-minimized models are consistent with a general acid-catalyzed, in-line displacement of the phosphate moiety to Cys(403) On the enzym e, followed by attack by a nucleophilic water molecule to release orth ophosphate, This nucleophilic water molecule is identified in the crys tal structure of the nitrate complex, The active site structure of the PTPase is compared to alkaline phosphatase, which employs a similar p hosphomonoester hydrolysis mechanism, Both enzymes must stabilize char ges at the nucleophile, the PO3 moiety of the transition state, and th e leaving group, Both an associative (bond formation preceding bond cl eavage) and a dissociative (bond cleavage preceding bond formation) me chanism were modeled, but a dissociative-like mechanism is favored for steric and chemical reasons, Since nearly all of the 47 invariant or highly conserved residues of the PTPase domain are clustered at the ac tive site, we suggest that the mechanism postulated for the Yersinia e nzyme is applicable to all the PTPases.