Crystallographic Trapping of Reaction Intermediates in Quinolinic Acid Synthesis by NadA

Anne Volbeda, Jaione Saez Cabodevilla, Claudine Darnault, Océane Gigarel, Thi-Hong-Lien Han, Oriane Renoux, Olivier Hamelin, Sandrine Ollagnier-de-Choudens, Patricia Amara, Juan C. Fontecilla-Camps

Index: 10.1021/acschembio.7b01104

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Abstract

NadA is a multifunctional enzyme that condenses dihydroxyacetone phosphate (DHAP) with iminoaspartate (IA) to generate quinolinic acid (QA), the universal precursor of the nicotinamide adenine dinucleotide (NAD(P)) cofactor. Using X-ray crystallography, we have (i) characterized two of the reaction intermediates of QA synthesis using a “pH-shift” approach and a slowly reacting Thermotoga maritima NadA variant and (ii) observed the QA product, resulting from the degradation of an intermediate analogue, bound close to the entrance of a long tunnel leading to the solvent medium. We have also used molecular docking to propose a condensation mechanism between DHAP and IA based on two previously published Pyrococcus horikoshi NadA structures. The combination of reported data and our new results provide a structure-based complete catalytic sequence of QA synthesis by NadA.