Dataset Information

Kinetic Isotope Effects and Transition State Structure for Human Phenylethanolamine N-Methyltransferase.

ABSTRACT: Phenylethanolamine N-methyltransferase (PNMT) catalyzes the S-adenosyl-l-methionine (SAM)-dependent conversion of norepinephrine to epinephrine. Epinephrine has been associated with critical processes in humans including the control of respiration and blood pressure. Additionally, PNMT activity has been suggested to play a role in hypertension and Alzheimer's disease. In the current study, labeled SAM substrates were used to measure primary methyl-14C and 36S and secondary methyl-3H, 5'-3H, and 5'-14C intrinsic kinetic isotope effects for human PNMT. The transition state of human PNMT was modeled by matching kinetic isotope effects predicted via quantum chemical calculations to intrinsic values. The model provides information on the geometry and electrostatics of the human PNMT transition state structure and indicates that human PNMT catalyzes the formation of epinephrine through an early SN2 transition state in which methyl transfer is rate-limiting.

SUBMITTER: Stratton CF

PROVIDER: S-EPMC5553282 | biostudies-literature | 2017 Feb

REPOSITORIES: biostudies-literature

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Kinetic Isotope Effects and Transition State Structure for Human Phenylethanolamine N-Methyltransferase.

Stratton Christopher F CF Poulin Myles B MB Du Quan Q Schramm Vern L VL

ACS chemical biology 20161228 2

Phenylethanolamine N-methyltransferase (PNMT) catalyzes the S-adenosyl-l-methionine (SAM)-dependent conversion of norepinephrine to epinephrine. Epinephrine has been associated with critical processes in humans including the control of respiration and blood pressure. Additionally, PNMT activity has been suggested to play a role in hypertension and Alzheimer's disease. In the current study, labeled SAM substrates were used to measure primary methyl-<sup>14</sup>C and <sup>36</sup>S and secondary ...[more]

PMID: 27997103

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Project description:Protein lysine methyltransferases (PKMTs) catalyze the methylation of protein substrates, and their dysregulation has been linked to many diseases, including cancer. Accumulated evidence suggests that the reaction path of PKMT-catalyzed methylation consists of the formation of a cofactor(cosubstrate)-PKMT-substrate complex, lysine deprotonation through dynamic water channels, and a nucleophilic substitution (SN2) transition state for transmethylation. However, the molecular characters of the proposed process remain to be elucidated experimentally. Here we developed a matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) method and corresponding mathematic matrix to determine precisely the ratios of isotopically methylated peptides. This approach may be generally applicable for examining the kinetic isotope effects (KIEs) of posttranslational modifying enzymes. Protein lysine methyltransferase SET8 is the sole PKMT to monomethylate histone 4 lysine 20 (H4K20) and its function has been implicated in normal cell cycle progression and cancer metastasis. We therefore implemented the MS-based method to measure KIEs and binding isotope effects (BIEs) of the cofactor S-adenosyl-l-methionine (SAM) for SET8-catalyzed H4K20 monomethylation. A primary intrinsic 13C KIE of 1.04, an inverse intrinsic ?-secondary CD3 KIE of 0.90, and a small but statistically significant inverse CD3 BIE of 0.96, in combination with computational modeling, revealed that SET8-catalyzed methylation proceeds through an early, asymmetrical SN2 transition state with the C-N and C-S distances of 2.35-2.40 Å and 2.00-2.05 Å, respectively. This transition state is further supported by the KIEs, BIEs, and steady-state kinetics with the SAM analog Se-adenosyl-l-selenomethionine (SeAM) as a cofactor surrogate. The distinct transition states between protein methyltransferases present the opportunity to design selective transition-state analog inhibitors.

Dataset Information

Kinetic Isotope Effects and Transition State Structure for Human Phenylethanolamine N-Methyltransferase.

Publications

Kinetic Isotope Effects and Transition State Structure for Human Phenylethanolamine N-Methyltransferase.

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