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首页> 外文期刊>Journal of Molecular Biology >A structural basis for transition-state stabilization in antibody-catalyzed hydrolysis: Crystal structures of an abzyme at 1.8 angstrom resolution
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A structural basis for transition-state stabilization in antibody-catalyzed hydrolysis: Crystal structures of an abzyme at 1.8 angstrom resolution

机译：抗体催化水解中过渡态稳定的结构基础：1.8埃分辨率的抗体酶的晶体结构

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The three-dimensional structure of a catalytic antibody, 6D9, has been solved as a complex with a transition state analog. The structure was determined from two different crystal forms, and was refined at a resolution of 1.8 A. The antibody 6D9, which was induced by immunization with the phosphonate transition state analog 3, hydrolyzes a prodrug of chloramphenicol monoester 1 to generate the parent drug 2. The kinetic studies have shown that the antibody is catalytic by virtue of the theoretical relationship between the affinity for the transition state and the catalytic efficiency (k(cat)/k(uncat) = K-S/K-TSA). The crystal structure makes it possible to visualize the theoretical relationship. A side-chain (N-epsilon) of His(L27D) is placed in a key position to make a hydrogen bond to the phosphonate oxygen of the transition state analog with a distance of 2.72 Angstrom, suggesting a hydrogen bond to the oxyanion developing in the transition state of the hydrolysis. There are no catalytic residues, other than the histidine, around the phosphonate moiety. Ln addition, in the antibody-hapten complex, the hapten bears a folded conformation and the two stacked aromatic rings are buried deep in the antigen-combining site through aromatic-aromatic interaction with Trp(H1001) and Tyr(H58). Th, con formation of the bound hapten suggests that the antibody binds the substrate to change the conformation of the ester moiety to a thermodynamically unstable E-form, thereby making it easy for the substrate to reach the transition-state during catalysis. These observations reveal that the catalytic mechanism is explained purely on the basis of the stabilization of the transition state. The refined high resolution structures reported here are envisaged to have an impact on the understanding of other hydrolytic antibodies, since their haptens share some unique features with the hapten used in this study. (C) 1998 Academic Press. [References: 45]
机译：催化抗体6D9的三维结构已作为具有过渡态类似物的复合物得以解决。由两种不同的晶体形式确定结构，并以1.8 A的分辨率精制。通过用膦酸酯过渡态类似物3免疫诱导的抗体6D9水解氯霉素单酯1的前药，从而生成母体药物2。动力学研究表明，由于对过渡态的亲和力与催化效率之间的理论关系（k（cat）/ k（uncat）= KS / K-TSA），抗体具有催化作用。晶体结构使得可视化理论关系成为可能。将His（L27D）的侧链（N-ε）置于关键位置以与过渡态类似物的膦酸酯氧形成氢键，间距为2.72埃，表明与水解的过渡态。除组氨酸外，在膦酸酯部分周围没有催化残基。另外，在抗体-半抗原复合物中，半抗原具有折叠构象，并且两个堆叠的芳环通过与Trp（H1001）和Tyr（H58）的芳族-芳族相互作用而深埋在抗原结合位点中。因此，结合的半抗原的形成表明抗体结合底物以将酯部分的构象改变为热力学不稳定的E-形式，从而使底物在催化过程中易于达到过渡态。这些观察结果表明，仅在过渡态稳定的基础上解释了催化机理。由于此处的半抗原与本研究中使用的半抗原具有某些独特的功能，因此，本文报道的精制高分辨率结构有望影响其他水解抗体的理解。 （C）1998年学术出版社。 [参考：45]

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