Co-C bond activation in methylmalonyl-CoA mutase by stabilization of the post-homolysis product CO2+ cobalamin
Co-C bond activation in methylmalonyl-CoA mutase by stabilization of the post-homolysis product CO2+ cobalamin
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DOI：
10.1021/ja0503736
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发表时间：
2005-11-30
影响因子：
15
通讯作者：
Brunold, TC
中科院分区：
文献类型：
--
作者：
Brooks, AJ;Vlasie, M;Brunold, TC
尽管进行了数十年的研究，辅酶B-12（腺苷钴胺素，腺苷Cbl）依赖性酶促进辅因子的Co-C键的均裂以启动催化的机制仍然困扰着研究人员。在这项工作中，我们利用磁性圆二色谱来探索还原的B12辅因子的电子结构（即，后均裂产物Co 2 + Cb I）由甲基丙二酰辅酶A β酶调节。我们的数据揭示了一个相当均匀的稳定的Co 3d轨道相对于咕啉PI/PI* 为基础的分子轨道时，Co 2 +CbI结合到酶的活性位点，特别是在底物的存在下。相反，我们以前的研究（布鲁克斯，A. J.道：Vlasie，M.; Banerjee，R.; Brunold，T. C. J. Am. 2004，126，8167-8180）。表明，当CO_2-Cbl与MMCM活性位点结合时，即使在底物（类似物）存在下，也不会发生CO（3+）Cbl电子结构的酶促扰动。总的来说，这些观察结果提供了直接的证据，酶促Co-C键活化涉及均裂后产物CO2+- Cbl的稳定，而不是CO（3+）Cbl“基态”的不稳定。
Despite decades of research, the mechanism by which coenzyme B-12 (adenosylcobalamin, AdoCbl)-dependent enzymes promote homolytic cleavage of the cofactor's Co-C bond to initiate catalysis has continued to elude researchers. In this work, we utilized magnetic circular dichroism spectroscopy to explore how the electronic structure of the reduced B12 cofactor (i.e., the post-homolysis product Co2+CbI) is modulated by the enzyme methylmalonyl-CoA mutase. Our data reveal a fairly uniform stabilization of the Co 3d orbitals relative to the corrin pi/pi*-based molecular orbitals when Co2+CbI is bound to the enzyme active site, particularly in the presence of substrate. Contrastingly, our previous studies (Brooks, A. J.; Vlasie, M.; Banerjee, R.; Brunold, T. C. J. Am. Chem. Soc. 2004, 126, 8167-8180.) showed that when AdoCbl is bound to the MMCM active site, no enzymatic perturbation of the CO(3+)Cbl electronic structure occurs, even in the presence of substrate (analogues). Collectively, these observations provide direct evidence that enzymatic Co-C bond activation involves stabilization of the post-homolysis product, CO2+- Cbl, rather than destabilization of the CO(3+)Cbl "ground" state.