SSF51726

UROD/MetE-like

SUPERFAMILY entry
Member databaseSUPERFAMILY
SUPERFAMILY typehomologous superfamily

Description
Imported from IPR038071

Uroporphyrinogen decarboxylase (URO-D), the fifth enzyme of the haem biosynthetic pathway, catalyses the sequential decarboxylation of the four acetyl side chains of uroporphyrinogen to yield coproporphyrinogen
[3]
. URO-D deficiency is responsible for the human genetic diseases familial porphyria cutanea tarda (fPCT) and hepatoerythropoietic porphyria (HEP). The sequence of URO-D has been well conserved throughout evolution. The best conserved region is located in the N-terminal section; it contains a perfectly conserved hexapeptide. There are two arginine residues in this hexapeptide which could be involved in the binding, via salt bridges, to the carboxyl groups of the propionate side chains of the substrate.

Methionine synthases catalyse the the final step of methionine biosynthesis. Two apparently unrelated families of proteins catalyse this step: cobalamin-dependent methionine synthase, which catalyses the transfer of a methyl group from N5-methyltetrahydrofolate to L-homocysteine and requires cobalamin as a cofactor (MetH; 5-methyltetrahydrofolate:L-homocysteine S-methyltransferase;
2.1.1.13
) and cobalamin-independent methionine synthase, which catalyses the transfer of a methyl group from methyltetrahydrofolate to L-homocysteine without using an intermediate methyl carrier (MetE; 5-methyltetrahydropteroyltri-L-glutamate:L-homocysteine S-methyltransferase;
2.1.1.14
). These enzymes display no detectable sequence homology between them, but both require zinc for activation and binding to L-homocysteine. Organisms that cannot obtain cobalamin (vitamin B12) encode only the cobalamin-independent enzyme. Escherichia coli and many other bacteria express both enzymes
[2]
. Mammals utilise only cobalamin-dependent methionine synthase, while plants and yeasts utilise only the cobalamin-independent enzyme.

The crystal structure of human uroporphyrinogen decarboxylase (URO-D) shows it is comprised of a single domain containing a (β/α)8-barrel with a deep active site cleft formed by loops at the C-terminal ends of the barrel strands
[4]
. The cobalamin-independent methionine synthase MetE consists of a duplication of a related domain. Each domain is a (β/α)8-barrel with extended β-α loops. The barrels are arranged face to face and the extended β-α loops form the interface
[1]
.

References
Imported from IPR038071

1.Structural analysis of a fungal methionine synthase with substrates and inhibitors. Ubhi D, Kago G, Monzingo AF, Robertus JD. J. Mol. Biol. 426, 1839-47, (2014). View articlePMID: 24524835

2.Comparison of cobalamin-independent and cobalamin-dependent methionine synthases from Escherichia coli: two solutions to the same chemical problem. Gonzalez JC, Banerjee RV, Huang S, Sumner JS, Matthews RG. Biochemistry 31, 6045-56, (1992). View articlePMID: 1339288

3.Uroporphyrinogen decarboxylase in Saccharomyces cerevisiae. HEM12 gene sequence and evidence for two conserved glycines essential for enzymatic activity. Garey JR, Labbe-Bois R, Chelstowska A, Rytka J, Harrison L, Kushner J, Labbe P. Eur. J. Biochem. 205, 1011-6, (1992). View articlePMID: 1576986

4.Crystal structure of human uroporphyrinogen decarboxylase. Whitby FG, Phillips JD, Kushner JP, Hill CP. EMBO J. 17, 2463-71, (1998). View articlePMID: 9564029

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