Heterotetrameric sarcosine oxidase: structure of a diflavin metalloenzyme at 1.85 A resolution

J Mol Biol. 2006 Jul 28;360(5):1000-18. doi: 10.1016/j.jmb.2006.05.067. Epub 2006 Jun 15.


The crystal structure of heterotetrameric sarcosine oxidase (TSOX) from Pseudomonas maltophilia has been determined at 1.85 A resolution. TSOX contains three coenzymes (FAD, FMN and NAD+), four different subunits (alpha, 103 kDa; beta, 44 kDa; gamma, 21 kDa; delta, 11 kDa) and catalyzes the oxidation of sarcosine (N-methylglycine) to yield hydrogen peroxide, glycine and formaldehyde. In the presence of tetrahydrofolate, the oxidation of sarcosine is coupled to the formation of 5,10-methylenetetrahydrofolate. The NAD+ and putative folate binding sites are located in the alpha-subunit. The FAD binding site is in the beta-subunit. FMN is bound at the interface of the alpha and beta-subunits. The FAD and FMN rings are separated by a short segment of the beta-subunit with the closest atoms located 7.4 A apart. Sulfite, an inhibitor of oxygen reduction, is bound at the FMN site. 2-Furoate, a competitive inhibitor with respect to sarcosine, is bound at the FAD site. The sarcosine dehydrogenase and 5,10-methylenetetrahydrofolate synthase sites are 35 A apart but connected by a large internal cavity (approximately 10,000 A3). An unexpected zinc ion, coordinated by three cysteine and one histidine side-chains, is bound to the delta-subunit. The N-terminal half of the alpha subunit of TSOX (alphaA) is closely similar to the FAD-binding domain of glutathione reductase but with NAD+ replacing FAD. The C-terminal half of the alpha subunit of TSOX (alphaB) is similar to the C-terminal half of dimethylglycine oxidase and the T-protein of the glycine cleavage system, proteins that bind tetrahydrofolate. The beta-subunit of TSOX is very similar to monomeric sarcosine oxidase. The gamma-subunit is similar to the C-terminal sub-domain of alpha-TSOX. The delta-subunit shows little similarity with any PDB entry. The alphaA domain/beta-subunit sub-structure of TSOX closely resembles the alphabeta dimer of L-proline dehydrogenase, a heteroctameric protein (alphabeta)4 that shows highest overall similarity to TSOX.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Binding Sites
  • Catalytic Domain
  • Coenzymes / chemistry
  • Crystallography, X-Ray
  • Glycine / chemistry
  • Hydrogen Bonding
  • Leucovorin / chemistry
  • Models, Molecular*
  • Oxidation-Reduction
  • Protein Binding
  • Protein Conformation
  • Protein Subunits / chemistry
  • Pseudomonas / enzymology*
  • Sarcosine / chemistry
  • Sarcosine Oxidase / chemistry*
  • Sulfites / chemistry
  • Tetrahydrofolates / chemistry
  • Zinc / chemistry


  • Coenzymes
  • Protein Subunits
  • Sulfites
  • Tetrahydrofolates
  • 5,6,7,8-tetrahydrofolic acid
  • Sarcosine Oxidase
  • Zinc
  • Leucovorin
  • Glycine
  • Sarcosine

Associated data

  • PDB/2GAG
  • PDB/2GAH