Thorn S N, Daniels R G, Auditor M T, Hilvert D
Department of Chemistry, Scripps Research Institute, La Jolla, California 92037.
Nature. 1995 Jan 19;373(6511):228-30. doi: 10.1038/373228a0.
General acid-base catalysis contributes substantially to the efficacy of many enzymes, enabling an impressive array of eliminations, isomerizations, racemizations, hydrolyses and carbon-carbon bond-forming reactions to be carried out with high rates and selectivities. The fundamental challenge of exploiting similar effects in designed catalysts such as catalytic antibodies is that of correctly positioning the catalytic groups in an appropriate active-site microenvironment. Charge complementarity between antibody and hapten (the template used to induce an antibody) has been used successfully in a number of instances to elicit acids and bases within immunoglobulin combining sites, but the activities of the catalysts obtained by this strategy are generally considerably lower than those of natural enzymes. Here we report that by optimizing hapten design and efficiently screening the immune response, antibodies can be obtained that act effectively as general base catalysts. Thus a cationic hapten correctly mimicking the transition-state geometry of all reacting bonds and bearing little resemblance to the reaction product has yielded carboxylate-containing antibodies that catalyse an E2 elimination with more than 10(3) turnovers per active site and rate accelerations of greater than 10(8). These results demonstrate that very large effects can be achieved by strategic use of haptenic charge.
一般酸碱催化对许多酶的催化效率有重要贡献，能使一系列令人印象深刻的消除反应、异构化反应、外消旋化反应、水解反应以及碳 - 碳键形成反应以高反应速率和高选择性进行。在诸如催化抗体等设计催化剂中利用类似效应面临的根本挑战是，如何在合适的活性位点微环境中正确定位催化基团。抗体与半抗原（用于诱导抗体的模板）之间的电荷互补性已在许多情况下成功用于在免疫球蛋白结合位点内引发酸和碱，但通过该策略获得的催化剂的活性通常远低于天然酶。在此我们报告，通过优化半抗原设计并有效筛选免疫反应，可以获得能有效充当一般碱催化剂的抗体。因此，一种阳离子半抗原正确模拟了所有反应键的过渡态几何结构，且与反应产物几乎没有相似之处，它产生了含羧酸盐的抗体，这些抗体催化E2消除反应时每个活性位点的周转数超过10³，速率加速超过10⁸。这些结果表明，通过策略性地利用半抗原电荷可以实现非常大的效应。
