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The x-ray structure of the complex of a catalytic antibody Fab fragment with a phosphonate transition-state analog has been determined. The antibody (CNJ206) catalyzes the hydrolysis of p-nitrophenyl esters with significant rate enhancement and substrate specificity. Comparison of this structure with that of the uncomplexed Fab fragment suggests hapten-induced conformational changes: the shape of the combining site changes from a shallow groove in the uncomplexed Fab to a deep pocket where the hapten is buried. Three hydrogen-bond donors appear to stabilize the charged phosphonate group of the hapten: two NH groups of the heavy (H) chain complementarity-determining region 3 (H3 CDR) polypeptide chain and the side-chain of histidine-H35 in the H chain (His-H35) in the H1 CDR. The combining site shows striking structural similarities to that of antibody 17E8, which also has esterase activity. Both catalytic antibody ("abzyme") structures suggest that oxyanion stabilization plays a significant role in their rate acceleration. Additional catalytic groups that improve efficiency are not necessarily induced by the eliciting hapten; these groups may occur because of the variability in the combining sites of different monoclonal antibodies that bind to the same hapten.

Type

Journal article

Journal

Proc Natl Acad Sci U S A

Publication Date

05/12/1995

Volume

92

Pages

11721 - 11725

Keywords

Antibodies, Catalytic, Antibodies, Monoclonal, Binding Sites, Computer Simulation, Crystallography, Esterases, Haptens, Immunoglobulin Fab Fragments, Kinetics, Models, Molecular, Nitrophenols, Protein Conformation, Substrate Specificity, Synchrotrons