Heterotetrameric sarcosine oxidase: structure of a diflavin metalloenzyme at 1.85 A resolution.
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.
Chen
Zhi-wei
ZW
Washington University School of Medicine, St. Louis, MO 63110, USA.
Hassan-Abdulah
Alshaimaa
A
Zhao
Gouhua
G
Jorns
Marilyn Schuman
MS
Mathews
F Scott
FS
D001665:Binding Sites; D020134:Catalytic Domain; D003067:Coenzymes / Q000737:chemistry; D018360:Crystallography, X-Ray; D005998:Glycine / Q000737:chemistry; D006860:Hydrogen Bonding; D002955:Leucovorin / Q000737:chemistry; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011485:Protein Binding; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry; D011549:Pseudomonas / Q000201:enzymology*; D012521:Sarcosine / Q000737:chemistry; D050879:Sarcosine Oxidase / Q000737:chemistry*; D013447:Sulfites / Q000737:chemistry; D013763:Tetrahydrofolates / Q000737:chemistry; D015032:Zinc / Q000737:chemistry
D003067:Coenzymes; D021122:Protein Subunits; D013447:Sulfites; D013763:Tetrahydrofolates; C030371:5,6,7,8-tetrahydrofolic acid; D050879:Sarcosine Oxidase; D015032:Zinc; D002955:Leucovorin; D005998:Glycine; D012521:Sarcosine