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

自1986年首次报道催化抗体以来，已经产生了多种抗体，并发现它们可以催化从周环反应到酰胺键水解的化学转化。其中大多数是由过渡态类似物免疫引起的。但遗憾的是，其催化活性不够，抗体催化的反应多为酯水解反应。我们设计了一种称为异源免疫的新策略，其中动物连续免疫两种不同但结构相关的半抗原。在异源免疫后，宿主可能对次级半抗原产生交叉反应，并产生对初级半抗原和次级半抗原都有亲和力的抗体。当两个半抗原在过渡态类似物的结构中分别含有正电荷或负电荷时，该半抗原对的异源免疫提供了在抗体结合位点同时产生酸性和碱性催化残基的机会。与单一半抗原免疫相比，磷酸半抗原连续两次免疫，然后是胺半抗原的增强，诱导的催化抗体具有更高的加速速率。这些催化抗体大多数与半抗原、膦酸半抗原和胺半抗原都具有交叉反应性，并且催化活性被两种半抗原有效抑制。这些结果表明，异源免疫策略提供了一种将多个催化残基引入抗体结合位点的潜在手段。

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.