GTP cyclohydrolase II, RibA (IPR000926)

Short name: RibA

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.