GTP cyclohydrolase II, RibA (IPR000926)

Short name: RibA

Overlapping homologous superfamilies

Family relationships



GTP cyclohydrolase II (also known as ribA) catalyses the first committed step in the biosynthesis of riboflavin (vitamin b2). The enzyme converts GTP to 2,5-diamino-6-beta-ribosyl-4(3H)-pyrimidinone 5'-phosphate (APy), formate and pyrophosphate, and requires magnesium as a cofactor. In numerous bacteria and in plants, GTP cyclohydrolase II occurs in the C-terminal of a bifunctional enzyme known as ribBA, which also comprises an N-terminal 3,4-dihydroxy-2-butanone 4-phosphate synthase (DHBP_synthase, also known as RibB) (IPR000422). RibB catalyses the conversion of D-ribulose 5-phosphate to formate and 3,4-dihydroxy-2-butanone 4-phosphate [PMID: 10940330].

A paralogous protein is encoded in the genome of Streptomyces coelicolor, which converts GTP to 2-amino-5-formylamino-6-ribosylamino-4(3H)-pyrimidinone 5'-phosphate (FAPy), an activity that has otherwise been reported for unrelated GTP cyclohydrolases III [PMID: 17002314].

GO terms

Biological Process

GO:0009231 riboflavin biosynthetic process

Molecular Function

GO:0003935 GTP cyclohydrolase II activity

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.