Trifunctional enzyme that catalyzes three distinct reactions as part of the 'de novo' inosine monophosphate biosynthetic pathway. 5-phospho-beta-D-ribosylamine + ATP + glycine = ADP + H(+) + N(1)-(5-phospho-beta-D-ribosyl)glycinamide + phosphate (6S)-10-formyltetrahydrofolate + N(1)-(5-phospho-beta-D-ribosyl)glycinamide = (6S)-5,6,7,8-tetrahydrofolate + H(+) + N(2)-formyl-N(1)-(5-phospho-beta-D-ribosyl)glycinamide 2-formamido-N(1)-(5-O-phospho-beta-D-ribosyl)acetamidine + ATP = 5-amino-1-(5-phospho-beta-D-ribosyl)imidazole + ADP + H(+) + phosphate Binds 1 magnesium or manganese ion per subunit. Purine metabolism; IMP biosynthesis via de novo pathway; 5-amino-1-(5-phospho-D-ribosyl)imidazole from N(2)-formyl-N(1)-(5-phospho-D-ribosyl)glycinamide: step 2/2. Purine metabolism; IMP biosynthesis via de novo pathway; N(1)-(5-phospho-D-ribosyl)glycinamide from 5-phospho-alpha-D-ribose 1-diphosphate: step 2/2. Purine metabolism; IMP biosynthesis via de novo pathway; N(2)-formyl-N(1)-(5-phospho-D-ribosyl)glycinamide from N(1)-(5-phospho-D-ribosyl)glycinamide (10-formyl THF route): step 1/1. Homodimer. The N-terminal ATP-grasp domain carries the phosphoribosylamine--glycine ligase activity. The central AIRS domain carries the phosphoribosylformylglycinamidine cyclo-ligase activity. The C-terminal GART domain carries the phosphoribosylglycinamide formyltransferase activity. In the N-terminal section; belongs to the GARS family. In the central section; belongs to the AIR synthase family. In the C-terminal section; belongs to the GART family.