InterPro: IPR001468 Indole-3-glycerol phosphate synthase, central region

Indole-3-glycerol phosphate synthase (EC:4.1.1.48) (IGPS) catalyses the fourth step in the biosynthesis of tryptophan, the ring closure of 1-(2-carboxy-phenylamino)-1-deoxyribulose into indol-3-glycerol-phosphate. In some bacteria, IGPS is a single chain enzyme. In others, such as Escherichia coli, it is the N-terminal domain of a bifunctional enzyme that also catalyses N-(5'-phosphoribosyl)anthranilate isomerase (EC:5.3.1.24) (PRAI) activity (see IPR001240), the third step of tryptophan biosynthesis. In fungi, IGPS is the central domain of a trifunctional enzyme that contains a PRAI C-terminal domain and a glutamine amidotransferase (EC:2.4.2) (GATase) N-terminal domain (see IPR000991).

A structure of the IGPS domain of the bifunctional enzyme from the mesophilic bacterium E. coli (eIGPS) has been compared with the monomeric indole-3-glycerol phosphate synthase from the hyperthermophilic archaeon Sulfolobus solfataricus (sIGPS). Both are single-domain (beta/alpha)8 barrel proteins, with one (eIGPS) or two (sIGPS) additional helices inserted before the first beta strand [1].