WALDEN-INVERSION-ENFORCED TRANSITION-STATE STABILIZATION IN A PROTEIN-TYROSINE-PHOSPHATASE

The initial step of the dephosphorylation reaction of a tyrosine phosp hate substrate catalyzed by the low molecular weight bovine protein ty rosine phosphatase (BPTP) has been studied, making use of a combined q uantum mechanical and molecular mechanical approach in molecular dynam ics simulations. It was found that the enzyme favors a dianion substra te in the dephosphorylation reaction, which is consistent with experim ents but in contrast to a recent mechanistic proposal involving a mono anion phosphate. The computed activation free energy is ca. 14 kcal/mo l, in accord with the activation parameters determined in the present study from stopped-flow kinetics experiments. Structural analyses supp ort the finding that BPTP catalyzes dephosphorylation reactions by sta bilizing the transition state through Walden-inversion-enforced hydrog en-bonding interactions during the S(N)2 process.