title: Ab initio QM/MM study shows there is no general acid in the reaction catalyzed by 4-oxalocrotonate tautomerase.
abstract: 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.
authors.affiliation: Department of Chemistry, Duke University, Box 90346, Durham, North Carolina 27708-0346, USA.
authors.forename: G Andrés
authors.initials: GA
authors.lastname: Cisneros
authors.forename: Haiyan
authors.initials: H
authors.lastname: Liu
authors.forename: Yingkai
authors.initials: Y
authors.lastname: Zhang
authors.forename: Weitao
authors.initials: W
authors.lastname: Yang
mesh_terms: D000143:Acids / Q000737:chemistry / Q000378:metabolism; D002384:Catalysis; D003198:Computer Simulation; D007535:Isomerases / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D016958:Pseudomonas putida / Q000201:enzymology; D011789:Quantum Theory; D013816:Thermodynamics
chemical_list: D000143:Acids; C021918:4-oxalocrotonate tautomerase; D007535:Isomerases