Structure Guided Understanding of NAD<sup>+</sup> Recognition in Bacterial DNA Ligases Sushmita D. Lahiri Rong-Fang Gu Ning Gao Irene Karantzeni Grant K. Walkup Scott D. Mills 10.1021/cb200392g.s001 https://acs.figshare.com/articles/journal_contribution/Structure_Guided_Understanding_of_NAD_sup_sup_Recognition_in_Bacterial_DNA_Ligases/2539324 NAD<sup>+</sup>-dependent DNA ligases (LigA) are essential bacterial enzymes that catalyze phosphodiester bond formation during DNA replication and repair processes. Phosphodiester bond formation proceeds through a 3-step reaction mechanism. In the first step, the LigA adenylation domain interacts with NAD<sup>+</sup> to form a covalent enzyme-AMP complex. Although it is well established that the specificity for binding of NAD<sup>+</sup> resides within the adenylation domain, the precise recognition elements for the initial binding event remain unclear. We report here the structure of the adenylation domain from <i>Haemophilus influenzae</i> LigA. This structure is a first snapshot of a LigA-AMP intermediate with NAD<sup>+</sup> bound to domain 1a in its open conformation. The binding affinities of NAD<sup>+</sup> for adenylated and nonadenylated forms of the <i>H. influenzae</i> LigA adenylation domain were similar. The combined crystallographic and NAD<sup>+</sup>-binding data suggest that the initial recognition of NAD<sup>+</sup> is via the NMN binding region in domain 1a of LigA. 2016-02-21 17:23:32 NAD Phosphodiester bond formation proceeds adenylation domain LigA adenylation domain catalyze phosphodiester bond formation Haemophilus influenzae LigA NMN binding region influenzae LigA adenylation domain domain 1 DNA