Albrecht-von-Haller Institute, Göttingen Center for Molecular Biosciences, Georg-August University Göttingen, 37077 Göttingen, Germany.
Nat Chem. 2013 Sep;5(9):762-7. doi: 10.1038/nchem.1728. Epub 2013 Aug 18.
It is recognized widely that enzymes promote reactions by providing a pathway that proceeds through a transition state of lower energy. In principle, further rate enhancements could be achieved if intermediates are prevented from relaxing to their lowest energy state, and thereby reduce the barrier to the subsequent transition state. Here, we report sub-ångström-resolution crystal structures of genuine covalent reaction intermediates of transketolase. These structures reveal a pronounced out-of-plane distortion of over 20° for the covalent bond that links cofactor and substrate, and a specific elongation of the scissile substrate carbon-carbon bond (d > 1.6 Å). To achieve these distortions, the protein's conformation appears to prevent relaxation of a substrate-cofactor intermediate. The results implicate a reduced barrier to the subsequent step that is consistent with an intermediate of raised energy and leads to a more efficient overall process.
人们普遍认识到，酶通过提供一条经过低能量过渡态的途径来促进反应。原则上，如果可以防止中间产物松弛到其最低能量状态，从而降低后续过渡态的能垒，就可以进一步提高反应速率。在这里，我们报告了转酮醇酶的真正共价反应中间体的亚埃分辨率晶体结构。这些结构显示出连接辅因子和底物的共价键明显的 20°以上的面外扭曲，以及裂解底物碳-碳键的特定伸长（d > 1.6 Å）。为了实现这些扭曲，蛋白质的构象似乎阻止了底物-辅因子中间体的松弛。研究结果表明，后续步骤的能垒降低，这与能量升高的中间产物一致，并导致更有效的整体过程。
