Generation of Efficient Tailormade Biocatalysts (Catalytic Antibodies) by Heterologous Immuniztion

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From the first report of catalytic antibodies in 1986, a variety of the antibodies has been generated and found to catalyze chemical transformations from peri-cyclic reactions to amido-bond hydrolyses. Most of them are elicited by immunization of transition-state analogs. However, unfortunately, the catalytic activities are not sufficient and the most of the reactions catalyzed by the antibodies are esterolytic hydrolysise. We have devised a new strategy called heterologous immunization wherein an animal is immunized in succession with two different but structurally related haptens. Upon heterologous immunization, the host may respond crossreactively to the secondary hapten and produce antibodies which have affinity for both of the primary and secondary hapten. When two haptens individually contain either a positive or negative charge incorporated in the structure of a transition-state analog, the heterologous immunization of this hapten pair provides an opportunity to simultaneously generate an acidic and an basic catalytic residue in an antibody combining site. Two successive immunization of phoshonate hapten, followed by a boost with amine hapten, induced catalytic antibodies with a higher rate acceleration compared with those obtained from immunization of a single hapten. The majority of these catalytic antibodies possessed cross-reactivities to both haptens, phoshonate and amine haptens, and the catalytic activities were effectively inhibited by both haptens. These results imply that the heterologous immunization strategy offers a potential means of introducing multiple catalytic residues into antibody combining site.