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Theoretical study of specific hydrogen-bonding effects on the bridging P-OR bond strength of phosphate monoester dianions.

It has been proposed that the driving force for the initial phosphoryl transfer step of protein tyrosine phosphatases (PTPases) could be activation of the substrate ROPO32- by means of an enforced hydrogen-bonding interaction between an aspartic general acid and the bridging oxygen atom O (Zhang et al. Biochemistry 1995, 34, 16088-16096). The potential catalytic effect of this type of interaction, with regard to P-OR bond cleavage, was investigated computationally through simple model systems in which an efficient intramolecular hydrogen bond can take place between a H-bond donor group and the bridging oxygen atom of the dianionic phosphate. The dielectric effect of the environment (epsilon = 1, 4, and 78) was also explored. The results indicate that this interaction causes significant lengthenings of the scissile P-OR bond in all media but with more extreme effects observed in the low dielectric fields epsilon = 1 and epsilon = 4. It is interesting that, in all cases examined, this interaction actually contributes to stabilize the reactant state while causing its P-OR bond to lengthen. Overall, our results support the idea that this specific hydrogen-bonding situation might well be used by PTPases as an important driving force for promoting phosphoryl transfer reactions through highly dissociative transition states.