TY - JOUR
T1 - Ab initio QM/MM study shows there is no general acid in the reaction catalyzed by 4-oxalocrotonate tautomerase
AU - Cisneros, G. Andrés
AU - Liu, Haiyan
AU - Zhang, Yingkai
AU - Yang, Weitao
PY - 2003/8/27
Y1 - 2003/8/27
N2 - The mechanism for the reaction catalyzed by the 4-oxalocrotonate tautomerase (4-OT) enzyme has been studied using a quantum mechanical/molecular mechanical (QM/MM) method developed in our laboratory. Total free energy barriers were obtained for the two steps involved in this reaction. In the first step, Pro-1 acts as a general base to abstract a proton from the third carbon of the substrate, 2-oxo-4-hexenedioate, creating a negative charge on the oxygen at C-2 of this substrate. In the second step, the same hydrogen abstracted by the N-terminal Pro-1 is shuttled back to the fifth carbon of the substrate to form the product, 2-oxo-3-hexenedioate. The calculated total free energy barriers are 14.54 and 16.45 kcal/mol for the first and second steps, respectively. Our calculations clearly show that there is no general acid in the reaction. Arg-39″, which is hydrogen bonded to the carboxylate group of the substrate, and an ordered water, which moves closer to the site of the charge formed in the transition state and intermediate, play the main role in transition state/intermediate stabilization without acting as general acids in the reaction.
AB - The mechanism for the reaction catalyzed by the 4-oxalocrotonate tautomerase (4-OT) enzyme has been studied using a quantum mechanical/molecular mechanical (QM/MM) method developed in our laboratory. Total free energy barriers were obtained for the two steps involved in this reaction. In the first step, Pro-1 acts as a general base to abstract a proton from the third carbon of the substrate, 2-oxo-4-hexenedioate, creating a negative charge on the oxygen at C-2 of this substrate. In the second step, the same hydrogen abstracted by the N-terminal Pro-1 is shuttled back to the fifth carbon of the substrate to form the product, 2-oxo-3-hexenedioate. The calculated total free energy barriers are 14.54 and 16.45 kcal/mol for the first and second steps, respectively. Our calculations clearly show that there is no general acid in the reaction. Arg-39″, which is hydrogen bonded to the carboxylate group of the substrate, and an ordered water, which moves closer to the site of the charge formed in the transition state and intermediate, play the main role in transition state/intermediate stabilization without acting as general acids in the reaction.
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U2 - 10.1021/ja029672a
DO - 10.1021/ja029672a
M3 - Article
C2 - 12926963
AN - SCOPUS:0042431983
SN - 0002-7863
VL - 125
SP - 10384
EP - 10393
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 34
ER -