This is a family of prokaryotic proteins with type I GTP cyclohydrolase activity. GTP cyclohydrolase I is the first enzyme of the de novo tetrahydrofolate biosynthetic pathway present in bacteria, fungi, and plants, and encoded in Escherichia coli by the folE gene; it is also the first enzyme of the biopterin (BH4) pathway in Homo sapiens[1]. The invariate, highly conserved glutamate residue at position 216 in Swiss:Q5F9K6 is likely to be the substrate ligand and the metal ligand is likely to be the cysteine at position 147. The enzyme is Zinc 2+ dependent [2].

1: Discovery of a new prokaryotic type I GTP cyclohydrolase family. El Yacoubi B, Bonnett S, Anderson JN, Swairjo MA, Iwata-Reuyl D, de Crecy-Lagard V; J Biol Chem. 2006;281:37586-37593. PMID:17032654

2: Zinc-independent folate biosynthesis: genetic, biochemical, and structural investigations reveal new metal dependence for GTP cyclohydrolase IB. Sankaran B, Bonnett SA, Shah K, Gabriel S, Reddy R, Schimmel P, Rodionov DA, de Crecy-Lagard V, Helmann JD, Iwata-Reuyl D, Swairjo MA; J Bacteriol. 2009;191:6936-6949. PMID:19767425