Quinolinic acid (QA) is a common intermediate in the biosynthesis of nicotinamide adenine dinticleotide (NAD) and its derivatives in all organisms 1 that synthesize the molecule de novo. In most prokaryotes, it is formed from the condensation of dihydroxyacetone phosphate (DHAP) and aspartate-enamine by the action of quinolinate synthase (NadA). NadA contains a [4Fe-4S] cluster cofactor with a unique, non-cysteinyl-ligated, iron ion (Pea), which is proposed to bind the hydroxyl group, of a postulated intermediate in the last step of the reaction to facilitate a dehydration. However, direct evidence for this role in catalysis has yet to be provided. Herein, we present the structure of NadA in the presence Of the product of its reaction, QA. We find that Ni and the C7 carboxylate group of QA ligate to Pea in a bidentate fashion, which is confirmed by Hyperfine Sublevel Correlation (HYSCORE) spectroscopy. This binding mode would place the CS hydroxyl group of the postulated final intermediate distal to Fea and virtually incapable of Coordinating to. it. The structure shows that three strictly conserved amino acids, Glu198, Tyr109, and Tyr23, are in close proximity to the bound product. Substitution of these amino acids with Gln, Phe, and Phe, respectively, leads to complete loss of activity.