reaction mechanism of the epimerase, overview. The reaction can be initiated by protonation of N-5 followed by deprotonation at the acidic C-19 of dihydroneopterin- or dihydromonapterin-type substrates. Epimerization at C-2 might result from reversal of the cleavage reaction without stereochemical control
reaction mechanism of the epimerase, overview. The reaction can be initiated by protonation of N-5 followed by deprotonation at the acidic C-19 of dihydroneopterin- or dihydromonapterin-type substrates. Epimerization at C-2 might result from reversal of the cleavage reaction without stereochemical control
the active site of FolX is predicted to comprise residues from two adjacent subunits, which suggests that the tetramer is essential for the activity of the enzyme. Formation of the octamer may play a role in the stability of enzyme FolX
enzymes, encoded by genes folX and folB, are involved in the tetrahydrofolate biosynthesis. The aldolase can use L-threo-dihydroneopterin and D-erythro-dihydroneopterin as substrates for the formation of 6-hydroxymethyldihydropterin, but it can also catalyze the epimerization of carbon 2' of dihydroneopterin and dihydromonapterinat appreciable velocity. The epimerase catalyzes the epimerization of carbon 2' in the triphosphates of dihydroneopterin and dihydromonapterin. The enzyme can also catalyze the cleavage of the position 6 side chain of several pteridine derivatives at a slow rate. The polarization of the 2'-hydroxy group of the substrate can serve as the initial reaction step for the aldolase as well as for the epimerase activity. Epimerase- as well as aldolase-type reactions can be catalyzed by both the FolB and FolX proteins
in Escherichia coli, L-monapterin is made from dihydromonapterin triphosphate after successive dephosphorylation and oxidation. Dihydromonapterin triphosphate is formed by an epimerase acting on C2' carbon of dihydroneopterin triphosphate, which is made from GTP by GTP cyclohydrolase I (EC 3.5.4.16)
tetrahydromonapterin formation requires both FolX and FolM, a dihydrofolate and dihydrobiopterin reductase. Tetrahydromonapterin is the physiological cofactor for phenylalanine hydroxylase, and tetrahydromonapterin can outrank folate as an end product of pterin biosynthesis, pterin pathway overview
tetrahydromonapterin formation requires both FolX and FolM, a dihydrofolate and dihydrobiopterin reductase. Tetrahydromonapterin is the physiological cofactor for phenylalanine hydroxylase, and tetrahydromonapterin can outrank folate as an end product of pterin biosynthesis, pterin pathway overview
the epimerase catalyzes one step of the tetrahydrofolate biosynthetic pathway, dihydroneopterin triphosphate is converted to dihydromonapterin triphosphate
enzymes, encoded by genes folX and folB, are involved in the tetrahydrofolate biosynthesis. The aldolase can use L-threo-dihydroneopterin and D-erythro-dihydroneopterin as substrates for the formation of 6-hydroxymethyldihydropterin, but it can also catalyze the epimerization of carbon 2' of dihydroneopterin and dihydromonapterinat appreciable velocity. The epimerase catalyzes the epimerization of carbon 2' in the triphosphates of dihydroneopterin and dihydromonapterin. The enzyme can also catalyze the cleavage of the position 6 side chain of several pteridine derivatives at a slow rate. The polarization of the 2'-hydroxy group of the substrate can serve as the initial reaction step for the aldolase as well as for the epimerase activity. Epimerase- as well as aldolase-type reactions can be catalyzed by both the FolB and FolX proteins
the enzyme protein is an octamer both in the crystal structure, and in solution formed by two tetramers. The monomeric enzyme structure comprises a four-stranded antiparallel sheet, composed of beta1 (residues 10-12 and 16-20), beta2 (residues 33-42), beta3 (residues 98-106) and beta4 (residues 114-121), structure comparisons, overview
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CRYSTALLIZATION (Commentary)
ORGANISM
UNIPROT
LITERATURE
purified recombinant enzyme, vapour diffusion method, mixing of 500 nl of 6 mg/ml protein in 20 mM Tris pH 7.5, 50 mM NaCl, with 500 nl of reservoir solution containing 40% v/v 1,2-propanediol, 100 mM HEPES, pH 7.5, 1 week, at room temperature, X-ray diffraction structure determination and analysis at 3.0 A resolution
construction of an Escherichia coli strain that lacks phenylalanine hydroxylase, PhhA, and in which the expression of Pseudomonas aeruginosa PhhA plus the recycling enzyme pterin 4a-carbinolamine dehydratase PhhB, rescues tyrosine auxotrophy. This rescue is abrogated by deleting folX or folM and restored by expressing the deleted gene from a plasmid. The folX deletion selectively eliminates tetrahydromonapterin production, the mutant strain lacks tetrahydromonapterin
deletion of tyrA (making PhhA the sole source of tyrosine) and folX results in a strain prototrophic for tyrosine, whereas the DELTAtyrA DELTAfolX strain is auxotrophic
deletion of tyrA (making PhhA the sole source of tyrosine) and folX results in a strain prototrophic for tyrosine, whereas the DELTAtyrA DELTAfolX strain is auxotrophic
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PURIFICATION (Commentary)
ORGANISM
UNIPROT
LITERATURE
native enzyme 954fold by ammonium sulfate fractionation, Cibacron blue 3GA affinity chromatography, hydrophobic interaction chromatography, methotrexate affinity chromatography, and ge filtration, to homogeneity
recombinant enzyme 2.7fold from Escherichia coli strain M15 by anion exchange chromatography, ultrafiltration, heat treatment at 80°C for 4 min, and gel filtration
Haumann, C.; Rohdich, F.; Schmidt, E.; Bacher, A.; Richter, G.
Biosynthesis of pteridines in Escherichia coli. Structural and mechanistic similarity of dihydroneopterin-triphosphate epimerase and dihydroneopterin aldolase
5.1.99.7 dihydroneopterin triphosphate 2'-epimerase
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