Department of Chemistry , University of Louisville , Louisville , Kentucky 40292 , United States.
Department of Theoretical Chemistry, Institute of Chemistry , University of Silesia in Katowice , Szkolna 9 , PL-40 006 Katowice , Poland.
J Phys Chem B. 2019 Mar 28;123(12):2585-2598. doi: 10.1021/acs.jpcb.8b07547. Epub 2019 Mar 13.
Glutamate mutase (GLM) is a coenzyme B-dependent enzyme that catalyzes the conversion of S-glutamate to (2 S,3 S)-3-methyl aspartate. The initial step in the catalytic process is the homolytic cleavage of the coenzyme's Co-C bond upon binding of a substrate. Alternatively, the Co-C bond can be cleaved using light. To investigate the photolytic cleavage of the Co-C bond in GLM, we applied a combined density functional theory/molecular mechanics (DFT/MM) and time-dependent-DFT/MM method to scrutinize the ground and the low-lying excited states. Potential energy surfaces (PESs) were generated as a function of axial bond lengths to describe the photodissociation mechanism. The S PES was characterized as the crossing of two electronic states, metal-to-ligand charge transfer (MLCT), and ligand field (LF). In GLM, radical pairs generate from the LF state. Two pathways, path A and path B, were identified as possible channels to connect the MLCT and LF electronic states. The S PES in GLM was compared with the S PES for coenzyme B-dependent ethanolamine ammonia lyase as well as the isolated AdoCbl cofactor. Finally, the theoretical insights related to the photodissociation mechanism were compared with transient absorption spectroscopy, electron paramagnetic resonance, and resonance Raman spectroscopy.
谷氨酸变位酶（GLM）是一种辅酶 B 依赖性酶，可催化 S-谷氨酸转化为（2S，3S）-3-甲基天冬氨酸。催化过程的初始步骤是在结合底物时辅酶 Co-C 键的均裂。或者，可以使用光来裂解 Co-C 键。为了研究 GLM 中 Co-C 键的光解断裂，我们应用了组合密度泛函理论/分子力学（DFT/MM）和时间相关 DFT/MM 方法来仔细研究基态和低能激发态。作为描述光解机制的轴向键长的函数生成势能面（PES）。S PES 的特征是两个电子态之间的交叉，即金属-配体电荷转移（MLCT）和配体场（LF）。在 GLM 中，自由基对从 LF 态生成。确定了两条可能的途径，途径 A 和途径 B，作为连接 MLCT 和 LF 电子态的可能通道。GLM 中的 S PES 与辅酶 B 依赖性乙醇胺氨裂解酶以及分离的 AdoCbl 辅因子的 S PES 进行了比较。最后，将与光解机制相关的理论见解与瞬态吸收光谱、电子顺磁共振和共振拉曼光谱进行了比较。
