1,3-Proton Transfer of Pyridoxal 5′-Phosphate Schiff Base in the Branched-Chain Aminotransferase: Concerted or Stepwise Mechanism?,The Journal of Physical Chemistry B

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1,3-Proton Transfer of Pyridoxal 5′-Phosphate Schiff Base in the Branched-Chain Aminotransferase: Concerted or Stepwise Mechanism?
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2023-12-22 , DOI: 10.1021/acs.jpcb.3c05875
Xue Li ₁ , Xiaoli Sun ₂

Affiliation

The branched-chain aminotransferase from Mycobacterium tuberculosis (MtIlvE) is a pyridoxal 5′-phosphate (PLP) dependent enzyme, and it is essential for the synthesis of the branched-chain amino acids. Ketimine is an important intermediate in the catalytic process. We have investigated the mechanism of ketimine formation and the energy landscape using the multiple computational methods. It is found that the 1,3-proton transfer involved in ketimine formation occurs through a stepwise process rather than a one-step process. Lys204 is identified as a key residue for ligand binding and as a base that abstracts the Cα proton from the PLP-Glu Schiff base, yielding a carbanionic intermediate. The first proton transfer is the rate-limiting step with an energy barrier of 17.8 kcal mol^–1. Our study disclosed the detailed pathway of the proton transfer from external aldimine to ketimine, providing novel insights into the catalytic mechanism of other PLP-dependent enzymes.

中文翻译：

支链转氨酶中吡哆醛 5'-磷酸希夫碱的 1,3-质子转移：协同机制还是逐步机制？

结核分枝杆菌( Mt IlvE) 的支链转氨酶是一种吡哆醛 5'-磷酸 (PLP) 依赖性酶，对于支链氨基酸的合成至关重要。酮亚胺是催化过程中的重要中间体。我们使用多种计算方法研究了酮亚胺形成的机制和能量景观。研究发现，酮亚胺形成中涉及的1,3-质子转移是通过逐步过程而不是一步过程发生的。 Lys204 被确定为配体结合的关键残基，也是从 PLP-Glu 希夫碱中提取 Cα 质子的碱基，产生碳负离子中间体。第一次质子转移是限速步骤，能垒为 17.8 kcal mol ^–1 。我们的研究揭示了质子从外部醛亚胺转移到酮亚胺的详细途径，为其他 PLP 依赖性酶的催化机制提供了新的见解。

更新日期：2023-12-22

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