AC   MF_00179;
DC   Protein; auto
TR   HAMAP; MF_00179; -; 1; level=0
XX
Names: RibA
XX
ID   RIBA
DE   RecName: Full=GTP cyclohydrolase-2;
DE            EC=3.5.4.25;
DE   AltName: Full=GTP cyclohydrolase II;
GN   Name=ribA;
XX
CC   -!- FUNCTION: Catalyzes the conversion of GTP to 2,5-diamino-6-
CC       ribosylamino-4(3H)-pyrimidinone 5'-phosphate (DARP), formate and
CC       pyrophosphate.
CC   -!- CATALYTIC ACTIVITY:
CC       Reaction=GTP + 4 H2O = 2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)-
CC         pyrimidine + formate + 3 H(+) + 2 phosphate; Xref=Rhea:RHEA:23704,
CC         ChEBI:CHEBI:15377, ChEBI:CHEBI:15378, ChEBI:CHEBI:15740,
CC         ChEBI:CHEBI:37565, ChEBI:CHEBI:43474, ChEBI:CHEBI:58614; EC=3.5.4.25;
CC   -!- COFACTOR:
CC       Name=Zn(2+); Xref=ChEBI:CHEBI:29105;
CC       Note=Binds 1 zinc ion per subunit.;
CC   -!- PATHWAY: Cofactor biosynthesis; riboflavin biosynthesis; 5-amino-6-(D-
CC       ribitylamino)uracil from GTP: step 1/4.
case <OC:Enterobacterales>
CC   -!- SUBUNIT: Homodimer.
end case
CC   -!- SIMILARITY: Belongs to the GTP cyclohydrolase II family.
XX
DR   Pfam; PF00925; GTP_cyclohydro2; 1; trigger=no
DR   NCBIfam; TIGR00505; RibA; 1; trigger=no
XX
KW   GTP-binding
KW   Hydrolase
KW   Metal-binding
KW   Nucleotide-binding
KW   Riboflavin biosynthesis
KW   Zinc
XX
GO   GO:0003935; F:GTP cyclohydrolase II activity
GO   GO:0008270; F:zinc ion binding
GO   GO:0009231; P:riboflavin biosynthetic process
XX
FT   From: RIBA_ECOLI (P0A7I7)
FT   BINDING         49..53
FT                   /ligand="GTP"
FT                   /ligand_id="ChEBI:CHEBI:37565"
FT   BINDING         92..94
FT                   /ligand="GTP"
FT                   /ligand_id="ChEBI:CHEBI:37565"
FT   Condition: E-G-R
FT   ACT_SITE        126
FT                   /note="Proton acceptor"
FT   Condition: D
FT   ACT_SITE        128
FT                   /note="Nucleophile"
FT   Condition: R
FT   BINDING         54
FT                   /ligand="Zn(2+)"
FT                   /ligand_id="ChEBI:CHEBI:29105"
FT                   /ligand_note="catalytic"
FT   Condition: C
FT   BINDING         65
FT                   /ligand="Zn(2+)"
FT                   /ligand_id="ChEBI:CHEBI:29105"
FT                   /ligand_note="catalytic"
FT   Condition: C
FT   BINDING         67
FT                   /ligand="Zn(2+)"
FT                   /ligand_id="ChEBI:CHEBI:29105"
FT                   /ligand_note="catalytic"
FT   Condition: C
FT   BINDING         70
FT                   /ligand="GTP"
FT                   /ligand_id="ChEBI:CHEBI:37565"
FT   Optional; Condition: Q
FT   BINDING         114
FT                   /ligand="GTP"
FT                   /ligand_id="ChEBI:CHEBI:37565"
FT   Condition: T
FT   BINDING         149
FT                   /ligand="GTP"
FT                   /ligand_id="ChEBI:CHEBI:37565"
FT   Condition: [TS]
FT   BINDING         154
FT                   /ligand="GTP"
FT                   /ligand_id="ChEBI:CHEBI:37565"
FT   Condition: K
XX
Size: 192-222;
Related: MF_01283!;
Template: P0A7I7; O08315;
Scope:
 Bacteria
 Archaea
Fusion:
 Nter: <ribB-like>; <Unknown>
 Cter: None
Duplicate: None
Plasmid: None
Comments: RibA and RibB are fused in some organisms (see MF_01283 for bifunctional RibBA).
 Some RibA are preceded by a ribB-like domain, which does not seem to code for DHBP synthase
 activity because it lacks all the residues important for activity.
 Fused with an unknown N-terminal domain in XYLFA and XYLFT.
 Possible wrong start in STRCO.
XX
# Revision 1.30 2023/06/01
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