title: A quantum chemical study of the ω-transaminase reaction mechanism.
abstract: ω-Transaminases are valuable tools in biocatalysis due to their stereospecificity and their broad substrate range. In the present study, the reaction mechanism of Chromobacterium violaceum ω-transaminase is investigated by means of density functional theory calculations. A large active site model is designed based on the recent X-ray crystal structure. The detailed energy profile for the half-transamination of (S)-1-phenylethylamine to acetophenone is calculated and the involved transition states and intermediates are characterized. The model suggests that the amino substrate forms an external aldimine with the coenzyme pyridoxal-5'-phosphate (PLP), through geminal diamine intermediates. The external aldimine is then deprotonated in the rate-determining step, forming a planar quinonoid intermediate. A ketimine is then formed, after which a hemiaminal is produced by the addition of water. Subsequently, the ketone product is obtained together with pyridoxamine-5'-phosphate (PMP). In the studied half-transamination reaction the ketone product is kinetically favored. The mechanism presented here will be valuable to enhance rational and semi-rational design of engineered enzyme variants in the development of ω-transaminase chemistry.
authors.affiliation: Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden. fahmi.himo@su.se.
authors.forename: Karim Engelmark
authors.initials: KE
authors.lastname: Cassimjee
authors.forename: Bianca
authors.initials: B
authors.lastname: Manta
authors.forename: Fahmi
authors.initials: F
authors.lastname: Himo
mesh_terms: D000098:Acetophenones / Q000737:chemistry; D000586:Amination; D020134:Catalytic Domain; D008958:Models, Molecular; D010627:Phenethylamines / Q000737:chemistry; D011789:Quantum Theory; D000637:Transaminases / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000098:Acetophenones; D010627:Phenethylamines; D000637:Transaminases; C038699:acetophenone