1gtp: Difference between revisions

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GTP CYCLOHYDROLASE I

OverviewOverview

BACKGROUND: Tetrahydrobiopterin serves as the cofactor for enzymes involved in neurotransmitter biosynthesis and as regulatory factor in immune cell proliferation and the biosynthesis of melanin. The biosynthetic pathway to tetrahydrobiopterin consists of three steps starting from GTP. The initial reaction is catalyzed by GTP cyclohdrolase I (GTP-CH-I) and involves the chemically complex transformation of the purine into the pterin ring system. RESULTS: The crystal structure of the Escherichia coli GTP-CH-I was solved by single isomorphous replacement and molecular averaging at 3.0 A resolution. The functional enzyme is a homodecameric complex with D5 symmetry, forming a torus with dimensions 65 A x 100 A. The pentameric subunits are constructed via an unprecedented cyclic arrangement of the four-stranded antiparallel beta-sheets of the five monomers to form a 20-stranded antiparallel beta-barrel of 35 A diameter. Two pentamers are tightly associated by intercalation of two antiparallel helix pairs positioned close to the subunit N termini. The C-terminal domain of the GTP-CH-I monomer is topologically identical to a subunit of the homohexameric 6-pyruvoyl tetrahydropterin synthase, the enzyme catalyzing the second step in tetrahydrobiopterin biosynthesis. CONCLUSIONS: The active site of GTP-CH-I is located at the interface of three subunits. It represents a novel GTP-binding site, distinct from the one found in G proteins, with a catalytic apparatus that suggest involvement of histidines and, possibly, a cystine in the unusual reaction mechanism. Despite the lack of significant sequence homology between GTP-CH-I and 6-pyruvoyl tetrahydropterin synthase, the two proteins, which catalyze consecutive steps in tetrahydrobiopterin biosynthesis, share a common subunit fold and oligomerization mode. In addition, the active centres have an identical acceptor site for the 2-amino-4-oxo pyrimidine moiety of their substrates which suggests an evolutionarily conserved protein fold designed for pterin biosynthesis.

About this StructureAbout this Structure

1GTP is a Single protein structure of sequence from Escherichia coli with as ligand. Active as GTP cyclohydrolase I, with EC number 3.5.4.16 Full crystallographic information is available from OCA.

ReferenceReference

Atomic structure of GTP cyclohydrolase I., Nar H, Huber R, Meining W, Schmid C, Weinkauf S, Bacher A, Structure. 1995 May 15;3(5):459-66. PMID:7663943

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-[[Image:1gtp.gif|left|200px]]<br /><applet load="1gtp" size="450" color="white" frame="true" align="right" spinBox="true"
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 caption="1gtp, resolution 3.0&Aring;" />
 '''GTP CYCLOHYDROLASE I'''<br />
 ==Overview==
-BACKGROUND: Tetrahydrobiopterin serves as the cofactor for enzymes, involved in neurotransmitter biosynthesis and as regulatory factor in, immune cell proliferation and the biosynthesis of melanin. The, biosynthetic pathway to tetrahydrobiopterin consists of three steps, starting from GTP. The initial reaction is catalyzed by GTP cyclohdrolase, I (GTP-CH-I) and involves the chemically complex transformation of the, purine into the pterin ring system. RESULTS: The crystal structure of the, Escherichia coli GTP-CH-I was solved by single isomorphous replacement and, molecular averaging at 3.0 A resolution. The functional enzyme is a, homodecameric complex with D5 symmetry, forming a torus with dimensions 65, A x 100 A. The pentameric subunits are constructed via an unprecedented, cyclic arrangement of the four-stranded antiparallel beta-sheets of the, five monomers to form a 20-stranded antiparallel beta-barrel of 35 A, diameter. Two pentamers are tightly associated by intercalation of two, antiparallel helix pairs positioned close to the subunit N termini. The, C-terminal domain of the GTP-CH-I monomer is topologically identical to a, subunit of the homohexameric 6-pyruvoyl tetrahydropterin synthase, the, enzyme catalyzing the second step in tetrahydrobiopterin biosynthesis., CONCLUSIONS: The active site of GTP-CH-I is located at the interface of, three subunits. It represents a novel GTP-binding site, distinct from the, one found in G proteins, with a catalytic apparatus that suggest, involvement of histidines and, possibly, a cystine in the unusual reaction, mechanism. Despite the lack of significant sequence homology between, GTP-CH-I and 6-pyruvoyl tetrahydropterin synthase, the two proteins, which, catalyze consecutive steps in tetrahydrobiopterin biosynthesis, share a, common subunit fold and oligomerization mode. In addition, the active, centres have an identical acceptor site for the 2-amino-4-oxo pyrimidine, moiety of their substrates which suggests an evolutionarily conserved, protein fold designed for pterin biosynthesis.
+BACKGROUND: Tetrahydrobiopterin serves as the cofactor for enzymes involved in neurotransmitter biosynthesis and as regulatory factor in immune cell proliferation and the biosynthesis of melanin. The biosynthetic pathway to tetrahydrobiopterin consists of three steps starting from GTP. The initial reaction is catalyzed by GTP cyclohdrolase I (GTP-CH-I) and involves the chemically complex transformation of the purine into the pterin ring system. RESULTS: The crystal structure of the Escherichia coli GTP-CH-I was solved by single isomorphous replacement and molecular averaging at 3.0 A resolution. The functional enzyme is a homodecameric complex with D5 symmetry, forming a torus with dimensions 65 A x 100 A. The pentameric subunits are constructed via an unprecedented cyclic arrangement of the four-stranded antiparallel beta-sheets of the five monomers to form a 20-stranded antiparallel beta-barrel of 35 A diameter. Two pentamers are tightly associated by intercalation of two antiparallel helix pairs positioned close to the subunit N termini. The C-terminal domain of the GTP-CH-I monomer is topologically identical to a subunit of the homohexameric 6-pyruvoyl tetrahydropterin synthase, the enzyme catalyzing the second step in tetrahydrobiopterin biosynthesis. CONCLUSIONS: The active site of GTP-CH-I is located at the interface of three subunits. It represents a novel GTP-binding site, distinct from the one found in G proteins, with a catalytic apparatus that suggest involvement of histidines and, possibly, a cystine in the unusual reaction mechanism. Despite the lack of significant sequence homology between GTP-CH-I and 6-pyruvoyl tetrahydropterin synthase, the two proteins, which catalyze consecutive steps in tetrahydrobiopterin biosynthesis, share a common subunit fold and oligomerization mode. In addition, the active centres have an identical acceptor site for the 2-amino-4-oxo pyrimidine moiety of their substrates which suggests an evolutionarily conserved protein fold designed for pterin biosynthesis.
 ==About this Structure==
-GTP is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli] with SO4 as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/GTP_cyclohydrolase_I GTP cyclohydrolase I], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.5.4.16 3.5.4.16] Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1GTP OCA].
+GTP is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli] with <scene name='pdbligand=SO4:'>SO4</scene> as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/GTP_cyclohydrolase_I GTP cyclohydrolase I], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.5.4.16 3.5.4.16] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1GTP OCA].
 ==Reference==
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 [[Category: purine hydrolysis]]
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