This domain is found at the C-terminal end of Pyrimidine/purine nucleotide 5'-monophosphate nucleosidase from Escherichia coli (PpnN, also known as YgdH) and similar proteins mainly found in gammaproteobacteria. PpnN is a nucleosidase that catalyses the hydrolysis of the N-glycosidic bond of diverse pyrimidine and purine nucleotide 5'-monophosphates. The binding of (p)ppGpp, an alarmone molecule that plays a role in the bacterial stringent response, gives rise to a large conformational change in the terminal region that leads to the exposure of the catalytic pocket. This domain shows a completely alpha-helical fold with an extension that wraps around the central domain [1, 2].

1: (p)ppGpp Regulates a Bacterial Nucleosidase by an Allosteric Two-Domain Switch. Zhang YE, Baerentsen RL, Fuhrer T, Sauer U, Gerdes K, Brodersen DE; Mol Cell. 2019;74:1239-1249. PMID:31023582

2: Nontargeted in vitro metabolomics for high-throughput identification of novel enzymes in Escherichia coli. Sevin DC, Fuhrer T, Zamboni N, Sauer U; Nat Methods. 2017;14:187-194. PMID:27941785