InterPro domain: IPR036144

This entry represents the RibA-like superfamily. Members in this superfamily includes GTP cyclohydrolase II, riboflavin biosynthesis protein RibBA and 3,4-dihydroxy-2-butanone 4-phosphate synthase.

GTP cyclohydrolase II (also known as ribA) catalyses the first committed step in the biosynthesis of riboflavin (vitamin b2). The enzyme converts GTP and water to formate, 2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)- pyrimidine andpyrophosphate, 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). RibB catalyses the conversion of D-ribulose 5-phosphate to formate and 3,4-dihydroxy-2-butanone 4-phosphate [ 1 ].

GTP cyclohydrolase II is absent in higher eukaryotes, which makes it a potential antimicrobial drug target. The structure of GTP cyclohydrolase II reveals both a different protein fold to eukaryotic GTP cyclohydrolase I and distinctive molecular recognition determinants for GTP [ 2 ].

1. Biosynthesis of vitamin b2 (riboflavin). Annu. Rev. Nutr. 20, 153-67
2. GTP cyclohydrolase II structure and mechanism. J. Biol. Chem. 280, 36912-9