| Title : Investigation of a general base mechanism for ester hydrolysis in C-C hydrolase enzymes of the alpha\/beta-hydrolase superfamily: a novel mechanism for the serine catalytic triad - Li_2007_Org.Biomol.Chem_5_507 |
| Author(s) : Li JJ , Bugg TD |
| Ref : Org Biomol Chem , 5 :507 , 2007 |
| Abstract : Previous mechanistic and crystallographic studies on two C-C hydrolase enzymes, Escherichia coli MhpC and Burkholderia xenovorans BphD, support a general base mechanism for C-C hydrolytic cleavage, rather than the nucleophilic mechanism expected for a serine hydrolase. The role of the active site serine residue could be to form a hydrogen bond with a gem-diolate intermediate, or to protonate such an intermediate. Hydrolase BphD is able to catalyse the hydrolysis of p-nitrophenyl benzoate ester substrates, which has enabled an investigation of these mechanisms using a Hammett analysis, and comparative studies upon five serine esterases and lipases from the alpha/beta-hydrolase family. A reaction parameter (rho) value of +0.98 was measured for BphD-catalysed ester hydrolysis, implying a build-up of negative charge in the transition state, consistent with a general base mechanism. Values of +0.31-0.61 were measured for other serine esterases and lipases, for the same series of esterase substrates. Pre-steady state kinetic studies of ester hydrolysis, using p-nitrophenyl acetate as the substrate, revealed a single step kinetic mechanism for BphD-catalysed ester hydrolysis, with no burst kinetics. A general base mechanism for BphD-catalysed ester hydrolysis is proposed, in which Ser-112 stabilises an oxyanion intermediate through hydrogen bonding, and assists the rotation of this oxyanion intermediate via proton transfer, a novel reaction mechanism for the serine catalytic triad. |
| ESTHER : Li_2007_Org.Biomol.Chem_5_507 |
| PubMedSearch : Li_2007_Org.Biomol.Chem_5_507 |
| PubMedID: 17252134 |
Li JJ, Bugg TD (2007)
Investigation of a general base mechanism for ester hydrolysis in C-C hydrolase enzymes of the alpha\/beta-hydrolase superfamily: a novel mechanism for the serine catalytic triad
Org Biomol Chem
5 :507
Li JJ, Bugg TD (2007)
Org Biomol Chem
5 :507