Phenylethanolamine N-methyltransferase

 

Phenylethanolamine N-methyltransferase (PNMT) is an enzyme that catalyses the synthesis of epinephrine from norepinephrine (NE) utilizing the cofactor S-adenosyl-L-methionine (AdoMet) as a methyl donor. Epinephrine is a naturally occurring hormone that increases cardiac output and raises glucose levels in the blood.

 

Reference Protein and Structure

Sequence
P11086 UniProt (2.1.1.28) IPR000940 (Sequence Homologues) (PDB Homologues)
Biological species
Homo sapiens (Human) Uniprot
PDB
1hnn - CRYSTAL STRUCTURE OF HUMAN PNMT COMPLEXED WITH SK&F 29661 AND ADOHCY(SAH) (2.4 Å) PDBe PDBsum 1hnn
Catalytic CATH Domains
3.40.50.150 CATHdb (see all for 1hnn)
Click To Show Structure

Enzyme Reaction (EC:2.1.1.28)

(R)-noradrenaline(1+)
CHEBI:72587ChEBI
+
S-adenosyl-L-methionine zwitterion
CHEBI:59789ChEBI
→
hydron
CHEBI:15378ChEBI
+
(R)-adrenaline(1+)
CHEBI:71406ChEBI
+
S-adenosyl-L-homocysteine zwitterion
CHEBI:57856ChEBI
Alternative enzyme names: Noradrenaline N-methyltransferase, Norepinephrine N-methyltransferase, Norepinephrine methyltransferase, Phenethanolamine N-methyltransferase, Phenethanolamine methyltransferase,

Enzyme Mechanism

Introduction

Phenyl ethanolamine N-methyltransferase catalyses the synthesis of epinephrine. This reaction has three major steps: The first step is the deprotonation of protonation of protonated norepinephrine, the second and the rate limiting step is the methyl transferring step and the last step is the deprotonation of the methylated norepinephrine.

Catalytic Residues Roles

UniProt PDB* (1hnn)
Glu219 Glu219A Acts as a nucleophile and deprotonates AdoHcy in the last step of catalysis. proton acceptor
Glu185 Glu185A Acts as a nucleophile and deprotonates Noradrenaline in the first step of catalysis. proton acceptor
*PDB label guide - RESx(y)B(C) - RES: Residue Name; x: Residue ID in PDB file; y: Residue ID in PDB sequence if different from PDB file; B: PDB Chain; C: Biological Assembly Chain if different from PDB. If label is "Not Found" it means this residue is not found in the reference PDB.

Chemical Components

proton transfer, bimolecular nucleophilic substitution, rate-determining step, overall reactant used

References

  1. Hou QQ et al. (2012), Biochim Biophys Acta, 1824, 533-541. QM/MM studies on the catalytic mechanism of phenylethanolamine N-methyltransferase. DOI:10.1016/j.bbapap.2012.01.017. PMID:22326747.
  2. Mahmoodi N et al. (2020), J Am Chem Soc, 142, 14222-14233. Transition-State Analogues of Phenylethanolamine N-Methyltransferase. DOI:10.1021/jacs.0c05446. PMID:32702980.

Step 1. The amine of Noradrenaline is deprotonated by Glu185 via a bridging water.

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Catalytic Residues Roles

Residue Roles
Glu185A proton acceptor

Chemical Components

proton transfer

Step 2. SN2 nucleophilic attack from the amine to AdoHcyn. This causes transfer of methyl group from AdoHcyn to NE.

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Catalytic Residues Roles

Residue Roles

Chemical Components

ingold: bimolecular nucleophilic substitution, rate-determining step

Step 3. Glu219 deprotonates the amine of AdoHcy via a bridging water.

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Catalytic Residues Roles

Residue Roles
Glu219A proton acceptor

Chemical Components

overall reactant used, proton transfer
Download: Image, Marvin File

Step 1. The amine of Noradrenaline is deprotonated by Glu185 via a bridging water.

Step 2. SN2 nucleophilic attack from the amine to AdoHcyn. This causes transfer of methyl group from AdoHcyn to NE.

Step 3. Glu219 deprotonates the amine of AdoHcy via a bridging water.

Products.

Contributors

Yordanos Abeje, Antonio Ribeiro