PurD

PurD is a gene that encodes phosphoribosylglycinamide synthetase, commonly referred to as GAR synthetase, a key enzyme in the de novo purine biosynthesis pathway. In bacteria, archaea, and eukaryotes where PurD is present, the enzyme catalyzes the ATP-dependent condensation of glycine with phosphoribosylamine (PRA) to form glycinamide ribonucleotide (GAR). The reaction uses one ATP molecule and produces ADP and inorganic phosphate as byproducts. GAR then serves as a precursor for subsequent steps that ultimately generate inosine monophosphate (IMP), the branch point for synthesis of AMP and GMP.

Genetic and functional context: PurD is typically encoded by the purD gene and is often found within purine biosynthesis gene clusters, such as the pur operon in bacteria. The enzyme is essential for viability in organisms that rely on de novo purine synthesis; disruption of purD usually results in purine auxotrophy unless exogenous purines are supplied.

Structure and characteristics: PurD proteins are generally around 300 amino acids in bacteria and function as cytosolic enzymes. They belong to the family of ATP-dependent amidoligases and usually display conserved motifs associated with ATP binding and substrate recognition. The enzyme often operates as a homodimer or higher-order oligomer in solution, with activity dependent on divalent metal ions, commonly Mg2+.

Regulation and relevance: PurD expression is typically coordinated with other pur genes and can respond to purine availability. Because it is part of a central biosynthetic pathway, PurD is studied as a potential target for antimicrobial strategies, as selective inhibition can disrupt purine production in pathogens without directly affecting human enzymes.