Structural Analysis of the NH3-dependent NAD~+ Synthetase from Deinococcus radiodurans

摘要

Nicotinamide adenine dinucleotide (NAD) is a ubiquitous molecule involved in both redox reactions as a cofactor and numerous regulatory processes as a substrate such as cell cycle, calcium signaling, immune response, and DNA repair.1 The biosynthesis of NAD~+ is vitally important in all living organisms and has been studied extensively in variety of species for antibiotic drug development. The NAD~+ is synthesized through two metabolic processes which are de novo and salvage pathways. Despite some variations in the early steps of two pathways, the final step of NAD~+ synthesis from nicotinic acid adenine dinucleotide (NaAD) to NAD~+ is highly conserved. NAD~+ synthetase (NADS, EC. 6.3.5.1) catalyzes conversion of NaAD to NAD~+ through two steps; first step is the adenylation of NaAD in the presence of ATP and Mg~(2+); second, the NAD-adenylate intermediate is attacked by nucleophilic ammonia leading to generate NAD~+ and AMP (Fig. 1(a)). The NADS family is categorized into two subgroups: (i) NH3-dependent NADS present only in prokaryotes, which has only synthetase domain (S-domain), and (ii) glutamine-dependent NADS present in all eukaryotes and some prokaryotes, which has an additional glutamine amide transfer domain (GAT-domain).