NUDT5 regulates purine metabolism and thiopurine sensitivity by interacting with PPAT

Cells generate purine nucleotides through de novo purine biosynthesis (DNPB) and purine salvage. Purine salvage represses DNPB to prevent excessive purine nucleotide synthesis through mechanisms that are incompletely understood. We identified Nudix hydrolase 5 (NUDT5) as a DNPB regulator. During purine salvage, NUDT5 suppresses DNPB independently of its catalytic function but rather through interaction with phosphoribosyl pyrophosphate amidotransferase (PPAT), the rate-limiting enzyme in the DNPB pathway. The NUDT5-PPAT interaction promoted PPAT oligomerization, suppressed PPAT's enzymatic activity, and facilitated disassembly of the purinosome, a metabolon that functions in DNPB. Disrupting the NUDT5-PPAT interaction overcame DNPB suppression during purine salvage, permitting excessive DNPB and inducing thiopurine resistance. Therefore, NUDT5 governs the balance between DNPB and salvage to maintain appropriate cellular purine nucleotide concentrations.