Themechanismofesterhydrolysishasbeenextensivelystudied;however,theprecisefunctionofactive-siteresiduesinpromotingcatalysisisunclear.WedescribeherethestructuralmodelsforthecomplexofacatalyticantibodyFvfragmentwithaphosphonatetransition-stateanalogue,constructedbyusinggenecloning,sequencingandmolecularmodeling,mainlybasedonaknownX-raystructureofacatalyticantibody.HydrophobicandelectrostaticanalysesoftheFv/analogandFv/substrateinteractionsuggestthehydrolysismechanism:TyrL91andTyrH97playimportantrolestostabilizetheβ-naphthylgroupofhaptenthroughπ-stack;HisH35donatesapairoffreeelectronsattheatomNE2toanactivewaterandletittobeapartialhydroxide,whichattacksthecarbonatomofthecarbonylgroupofthesubstrate.BothHisH35andArgL96canformhydrogenbondsandstabilizetheanionictetrahedralintermediateformedduringturnover.Thismechanismemphasizesthatanactivewaterbridgemaybeformedduringhydrolysisprocess.
