Lloyd S J, Lauble H, Prasad G S, Stout C D
Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Protein Sci. 1999 Dec;8(12):2655-62. doi: 10.1110/ps.8.12.2655.
The crystal structure of the S642A mutant of mitochondrial aconitase (mAc) with citrate bound has been determined at 1.8 A resolution and 100 K to capture this binding mode of substrates to the native enzyme. The 2.0 A resolution, 100 K crystal structure of the S642A mutant with isocitrate binding provides a control, showing that the Ser --> Ala replacement does not alter the binding of substrates in the active site. The aconitase mechanism requires that the intermediate product, cis-aconitate, flip over by 180 degrees about the C alpha-C beta double bond. Only one of these two alternative modes of binding, that of the isocitrate mode, has been previously visualized. Now, however, the structure revealing the citrate mode of binding provides direct support for the proposed enzyme mechanism.
已在1.8埃分辨率和100K条件下测定了与柠檬酸结合的线粒体乌头酸酶（mAc）S642A突变体的晶体结构，以捕捉底物与天然酶的这种结合模式。与异柠檬酸结合的S642A突变体在100K、2.0埃分辨率下的晶体结构提供了对照，表明丝氨酸到丙氨酸的替换不会改变活性位点中底物的结合。乌头酸酶机制要求中间产物顺乌头酸围绕Cα-Cβ双键翻转180度。这两种替代结合模式中，之前仅可视化了异柠檬酸模式。然而现在，揭示柠檬酸结合模式的结构为所提出的酶机制提供了直接支持。
