Information on EC 3.5.4.39 - GTP cyclohydrolase IV

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The expected taxonomic range for this enzyme is: Methanocaldococcus jannaschii

EC NUMBER
COMMENTARY hide
3.5.4.39
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RECOMMENDED NAME
GeneOntology No.
GTP cyclohydrolase IV
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REACTION
REACTION DIAGRAM
COMMENTARY hide
ORGANISM
UNIPROT
LITERATURE
GTP + H2O = 7,8-dihydroneopterin 2',3'-cyclic phosphate + formate + diphosphate
show the reaction diagram
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PATHWAY
BRENDA Link
KEGG Link
MetaCyc Link
6-hydroxymethyl-dihydropterin diphosphate biosynthesis II (Methanocaldococcus)
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6-hydroxymethyl-dihydropterin diphosphate biosynthesis V (Pyrococcus)
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6-hydroxymethyl-dihydropterin diphosphate biosynthesis
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SYSTEMATIC NAME
IUBMB Comments
GTP 7,8-8,9-dihydrolase (cyclizing, formate-releasing, diphosphate-releasing)
Requires Fe2+. A zinc protein. The enzyme is involved in methanopterin biosynthesis in methanogenic archaea. cf. GTP cyclohydrolase I (EC 3.5.4.16), GTP cyclohydrolase II (EC 3.5.4.25) and GTP cyclohydrolase IIa (EC 3.5.4.29).
ORGANISM
COMMENTARY hide
LITERATURE
UNIPROT
SEQUENCE DB
SOURCE
SUBSTRATE
PRODUCT                       
REACTION DIAGRAM
ORGANISM
UNIPROT
COMMENTARY
(Substrate) hide
LITERATURE
(Substrate)
COMMENTARY
(Product) hide
LITERATURE
(Product)
Reversibility
r=reversible
ir=irreversible
?=not specified
beta,gamma-methylene-GTP + H2O
?
show the reaction diagram
hydrolyzed at 10% of the specific activity compared to GTP
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?
GDP + H2O
?
show the reaction diagram
hydrolyzed at about 45% of the specific activity compared to GTP
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?
GTP + H2O
7,8-dihydroneopterin 2',3'-cyclic phosphate + formate + diphosphate
show the reaction diagram
GTP-gamma-S + H2O
?
show the reaction diagram
hydrolyzed at 130% of the specific activity compared to GTP
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?
additional information
?
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NATURAL SUBSTRATES
NATURAL PRODUCTS
REACTION DIAGRAM
ORGANISM
UNIPROT
COMMENTARY
(Substrate) hide
LITERATURE
(Substrate)
COMMENTARY
(Product) hide
LITERATURE
(Product)
REVERSIBILITY
r=reversible
ir=irreversible
?=not specified
GTP + H2O
7,8-dihydroneopterin 2',3'-cyclic phosphate + formate + diphosphate
show the reaction diagram
Q58185
the enzyme is involved in methanopterin biosynthesis in methanogenic archaea
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METALS and IONS
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
Fe2+
required. Mutation of conserved histidine residues H200N, H293N, and H295N, expected to be involved in Fe2+ binding, results in reduced enzymatic activity but no reduction in the amount of bound iron
Zn2+
0.5:1 molar ratio of zinc to enzyme monomer. The zinc content of the mutants H200N and H293N is similar to that of the wild type. Mutant H101N shows an increased amount of zinc (1:1 molar ratio of zinc to monomer)
INHIBITORS
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
7-methyl-GTP
included along with 2 mM GTP in the incubation mixture. 36% inhibition
dGTP
included along with 2 mM GTP in the incubation mixture. 28% inhibition
fapy-GMP
coincubation of MptA with fapyGMP (about 1 mM) and GTP (2 mM) results in a 5-fold reduction in activity
GMP
included along with 2 mM GTP in the incubation mixture. 43% inhibition
KM VALUE [mM]
SUBSTRATE
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
0.096
GTP
pH 7.2, 70°C
pH OPTIMUM
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
pH RANGE
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
6 - 7.5
pH 6.0: 55% of maximal activity, pH 7.5: about 40% of maximal activity
TEMPERATURE OPTIMUM
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
MOLECULAR WEIGHT
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
36300
2 * 36300, SDS-PAGE
37000
2 * 37000, SDS-PAGE
SUBUNITS
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
dimer
2 * 36300, SDS-PAGE; 2 * 37000, SDS-PAGE
TEMPERATURE STABILITY
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
80
10 min, 27% loss of activity
90
10 min, 60% loss of activity
100
10 min, 89% loss of activity
OXIDATION STABILITY
ORGANISM
UNIPROT
LITERATURE
the enzyme readily loses activity upon exposure to air. MptA loses all activity within 4 days at -20°C. This activity can be restored by adding specific divalent metal ions to the oxygen-inactivated enzyme under anaerobic conditions in the presence of dithiothreitol. Only Fe2+ is capable of restoring activity at the physiologically relevant concentrations of 0.020 mM. Higher concentrations of Mn2+ (0.2 mM) are able to restore activity to 24% of that seen with the Fe2+. At very high concentrations (2 mM) Mn2+ is able to restore MptA activity to a higher level than Fe2+. The Mn2+ enzyme is not inactivated by exposure to oxygen. The addition of reducing agents to the assay mixture is able to partially restore activity in oxygen inactivated MptA
685163
Purification/COMMENTARY
ORGANISM
UNIPROT
LITERATURE
Cloned/COMMENTARY
ORGANISM
UNIPROT
LITERATURE
expression in Escherichia coli
ENGINEERING
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
C163S-alkylcysteine
when incubated with N-ethylmaleimide, the enzyme loses 67% activity. Iodoacetamide reduces activity by 33%
E50D
no effect on specific activity of the enzyme
H101N
mutation does not affect the ability of the enzyme to form dihydro-D-neopterin 2',3'-cyclic phosphate nor does it have a reduced amount of iron
H200N/E50D
decrease in the specific activity
H293N
decrease in the specific activity
H295N
decrease in the specific activity; results in a majority of the protein being expressed in an insoluble form
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