PurN

PurN is a phosphoribosylglycinamide formyltransferase, an enzyme in de novo purine biosynthesis. It catalyzes the formylation of glycinamide ribonucleotide (GAR) to formylglycinamide ribonucleotide (FGAR) using 10-formyltetrahydrofolate as the one-carbon donor, releasing tetrahydrofolate. The reaction is GAR + 10-formyl-THF → FGAR + THF.

PurN is encoded by the purN gene in many bacteria and archaea and is a component of the purine biosynthesis operon. In contrast, some organisms possess an alternative GAR transformylase, PurT, which uses formate and ATP instead of 10-formyl-THF. PurN and PurT provide redundant GAR transformylase activity in different lineages.

Structure and mechanism: PurN belongs to the formyltransferase family; many bacterial PurN enzymes require metal ions (often Zn2+) in the active site and bind 10-formyl-THF and GAR to facilitate transfer of the formyl group. The enzyme generally forms a homodimer or homotetramer, with conserved active-site residues coordinating substrates.

Biological role: As a step in the early purine ribonucleotide biosynthesis pathway, PurN supplies FGAR for subsequent reactions leading to inosine monophosphate (IMP). Its activity is typically coordinated with other purine pathway enzymes and is subject to regulation by the cell’s purine nucleotide pool.

Clinical and research relevance: PurN is a potential target for antibiotics since it is essential in many bacteria but has structural differences from the human GART enzyme. Inhibitors of GAR transformylases have been explored in antimicrobial and metabolic cancer research.