Purinosome

The purinosome is a dynamic, multi-enzyme complex responsible for the de novo biosynthesis of purine nucleotides in eukaryotic cells. It is composed of six core enzymes that catalyze the ten-step conversion of phosphoribosyl pyrophosphate (PRPP) to inosine monophosphate (IMP), including the trifunctional GART protein (which contains the glycinamide ribonucleotide formyltransferase or GARFT domain) and the bifunctional ATIC protein (5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/IMP cyclohydrolase). The formation of this complex is highly regulated and occurs primarily under conditions of high purine demand, such as during rapid cell division, by facilitating substrate channeling and increasing metabolic flux. In clinical practice, the purinosome is a major therapeutic target, particularly in oncology and rheumatology. Antifolate drugs like pemetrexed and methotrexate exert their effects by inhibiting the transformylase domains (GARFT and AICARFT) within the complex or by disrupting the physical assembly of the purinosome itself. This inhibition leads to the depletion of essential purine pools, resulting in the inhibition of DNA and RNA synthesis and subsequent apoptosis in malignant or overactive immune cells. Genetic deficiencies in components of the complex, such as ATIC, lead to rare metabolic disorders like AICA-ribosiduria, highlighting the critical role of this assembly in human physiology.

Other names

GART-ATIC complexDe novo purine biosynthesis complexGlycinamide ribonucleotide formyltransferase / ATIC complexMultienzyme purine biosynthetic complex

Inhibition of transformylase activities (GARFT and AICARFT domains) and disruption of protein-protein interactions within the multienzyme assembly, leading to depletion of intracellular purine pools and arrest of DNA synthesis.