title: The reaction mechanism of phenylethanolamine N-methyltransferase: a density functional theory study.
abstract: Hybrid density functional theory methods were used to investigate the reaction mechanism of human phenylethanolamine N-methyltransferase (hPNMT). This enzyme catalyzes the S-adenosyl-L-methionine-dependent conversion of norepinephrine to epinephrine, which constitutes the terminal step in the catecholamine biosynthesis. Several models of the active site were constructed based on the X-ray structure. Geometries of the stationary points along the reaction path were optimized and the reaction barrier and energy were calculated and compared to the experimental values. The calculations demonstrate that the reaction takes place via an SN2 mechanism with methyl transfer being rate-limiting, a suggestion supported by mutagenesis studies. Optimal agreement with experimental data is reached using a model in which both active site glutamates are protonated. Overall, the mechanism of hPNMT is more similar to those of catechol O-methyltransferase and glycine N-methyltransferase than to that of guanidinoacetate N-methyltransferase in which methyl transfer is coupled to proton transfer.
authors.affiliation: Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, SE-106 91 Stockholm, Sweden.
authors.forename: Polina
authors.initials: P
authors.lastname: Georgieva
authors.forename: Qian
authors.initials: Q
authors.lastname: Wu
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McLeish
authors.forename: Fahmi
authors.initials: F
authors.lastname: Himo
mesh_terms: D019943:Amino Acid Substitution; D020134:Catalytic Domain; D002394:Catechol O-Methyltransferase / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D050938:Glycine N-Methyltransferase / Q000737:chemistry / Q000378:metabolism; D050937:Guanidinoacetate N-Methyltransferase / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010625:Phenylethanolamine N-Methyltransferase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D011994:Recombinant Proteins; C494506:GAMT protein, human; D050937:Guanidinoacetate N-Methyltransferase; C494510:GNMT protein, human; D050938:Glycine N-Methyltransferase; D010625:Phenylethanolamine N-Methyltransferase; D002394:Catechol O-Methyltransferase