Trimethylamine-N-oxide reductase (cytochrome c)

 

Trimethylamine N-oxide (TMAO) has been found in a variety of marine organisms including fish, molluscs, crustaceans and seaweed [PMID:16221580]. TMAO is found in marine organisms as an osmolyte in combination with urea. In sharks, who lack a swim bladder, TMAO and urea contribute to buoyancy. A number of marine-fish spoilage organisms use TMAO as an electron acceptor in anaerobic respiration [PMID:3904597]. Trimethylamine (TMA), the volatile product of this reaction, has the specific odour of rotting fish. In Escherichia coli, the TMAO respiratory chain consists of a quinol electron donor, a membrane-bound multiheme c-type cytochrome TorC, and a periplasmic terminal reductase TorA that contains bis(molybdopterin guanine dinucleotide)molybdenum cofactor (this entry). This molybdoenzyme belongs to the dimethyl sulfoxide (DMSO) reductase family.

 

Reference Protein and Structure

Sequence
O87948 UniProt (1.7.2.3) IPR011887 (Sequence Homologues) (PDB Homologues)
Biological species
Shewanella massilia (Bacteria) Uniprot
PDB
1tmo - TRIMETHYLAMINE N-OXIDE REDUCTASE FROM SHEWANELLA MASSILIA (2.5 Å) PDBe PDBsum 1tmo
Catalytic CATH Domains
3.40.228.10 CATHdb 3.40.50.740 CATHdb (see all for 1tmo)
Cofactors
Mo(=o)-bis(molybdopterin guanine dinucleotide)(4−) (1)
Click To Show Structure

Enzyme Reaction (EC:1.7.2.3)

iron(2+)
CHEBI:29033ChEBI
+
hydron
CHEBI:15378ChEBI
+
trimethylamine N-oxide
CHEBI:15724ChEBI
→
iron(3+)
CHEBI:29034ChEBI
+
water
CHEBI:15377ChEBI
+
trimethylammonium
CHEBI:58389ChEBI
Alternative enzyme names: TMAO reductase, TOR, Trimethylamine-N-oxide reductase (cytochrome c),

Enzyme Mechanism

Introduction

Mo(IV) is oxidised to Mo(VI) by two successive single electron transfers to the trimethylamine molecule. This transfer is stabilised by Ser149 and Trp118 that coordinate the molybdenum and the oxygen molecule which is transferred to the trimethylamine, respectively.

Catalytic Residues Roles

UniProt PDB* (1tmo)
Ser180, Trp149 Ser149(180)A, Trp118(149)A Forms part of the molybdenum binding site. electrostatic stabiliser
*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

redox reaction, electron transfer, bimolecular electrophilic addition, intermediate formation, overall product formed, intermediate collapse

References

  1. Czjzek M et al. (1998), J Mol Biol, 284, 435-447. Crystal structure of oxidized trimethylamine N-oxide reductase from Shewanella massilia at 2.5 A resolution. DOI:10.1006/jmbi.1998.2156. PMID:9813128.
  2. Fortino M et al. (2016), Phys Chem Chem Phys, 18, 8428-8436. Mechanistic investigation of trimethylamine-N-oxide reduction catalysed by biomimetic molybdenum enzyme models. DOI:10.1039/c5cp07278f. PMID:26932500.
  3. Cerqueira NM et al. (2015), J Biol Inorg Chem, 20, 323-335. Theoretical studies on mechanisms of some Mo enzymes. DOI:10.1007/s00775-015-1237-7. PMID:25698503.
  4. Iobbi-Nivol C et al. (2013), Biochim Biophys Acta Bioenerg, 1827, 1086-1101. Molybdenum enzymes, their maturation and molybdenum cofactor biosynthesis in Escherichia coli. DOI:https://doi.org/10.1016/j.bbabio.2012.11.007.
  5. Magalon A et al. (2011), Coord Chem Rev, 255, 1159-1178. Molybdenum enzymes in bacteria and their maturation. DOI:https://doi.org/10.1016/j.ccr.2010.12.031.
  6. McCrindle SL et al. (2005), Adv Microb Physiol, 50, 147-198. Microbial dimethylsulfoxide and trimethylamine-N-oxide respiration. DOI:10.1016/S0065-2911(05)50004-3. PMID:16221580.
  7. Johnson KE et al. (2001), J Biol Chem, 276, 13178-13185. An Active Site Tyrosine Influences the Ability of the Dimethyl Sulfoxide Reductase Family of Molybdopterin Enzymes to Reduce S-Oxides. DOI:10.1074/jbc.m010965200. PMID:11278798.
  8. Barrett EL et al. (1985), Annu Rev Microbiol, 39, 131-149. Bacterial reduction of trimethylamine oxide. DOI:10.1146/annurev.mi.39.100185.001023. PMID:3904597.

Step 1. The Ser149 stabilises the moco molybdenum by forming a coordination sphere and allowing the oxygen to donate electrons to the trimethylamine molecule. Trp118 also stabilises the transitional structure of the oxygen.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Ser149(180)A electrostatic stabiliser
Trp118(149)A electrostatic stabiliser, hydrogen bond donor

Chemical Components

redox reaction, electron transfer, ingold: bimolecular electrophilic addition, intermediate formation

Step 2. The transition state collapses by reducing the Mo5+ into a Mo4+ and releasing the oxygen atom to the trimethylamine turning it into trimethylamine N-oxide.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Ser149(180)A electrostatic stabiliser
Trp118(149)A electrostatic stabiliser

Chemical Components

overall product formed, redox reaction, intermediate collapse
Download: Image, Marvin File

Step 1. The Ser149 stabilises the moco molybdenum by forming a coordination sphere and allowing the oxygen to donate electrons to the trimethylamine molecule. Trp118 also stabilises the transitional structure of the oxygen.

Step 2. The transition state collapses by reducing the Mo5+ into a Mo4+ and releasing the oxygen atom to the trimethylamine turning it into trimethylamine N-oxide.

Products.

Contributors

Christian Drew, Craig Porter, Gemma L. Holliday, Marko Babić