High-resolution neutron structure of nicotinamide adenine dinucleotide

The structure of the free-acid form of the coenzyme NAD⁺ was determined at 100 K from a single-crystal neutron experiment. NAD⁺ is the oxidized form of the coenzyme redox pair NAD⁺/NADH and plays an important role in the catalysis of biological processes. The molecule crystallizes in space group P1 with one NAD⁺ and four water molecules per unit cell. The structure is compared with the previous X-ray models of NAD⁺ [Reddy et al. (1981), J. Am. Chem. Soc. 103, 907–914; Parthasarathy & Fridey (1984b), Science, 226, 969–971; Guillot et al. (2000), Acta Cryst. C56, 726–728]. The crystal packing and the hydrogen-bond pattern are discussed as well as four short C—­H...O contacts involving the pyridine and adenine rings. The structure displays stereochemical distortions owing to the hydrogen bonding and crystal-packing constraints, reflecting the adaptability of the NAD⁺ molecule in various chemical environments.