This is a conserved domain containing the catalytic zinc-metallopeptidase (HExxH) catalytic motif. Proteins containing this domain are found in some archaebacteria, as well as Helicobacter pylori. The proteins are 190-240 amino acids long, with the C terminus being the most conserved region, containing three conserved histidines [1,2,3,4]. This domain is found in YgjP from E. coli [4], a predicted metal-dependent hydrolase that hydrolyses UTP to UMP and diphosphate in vitro; and in MJ0123 from Methanocaldococcus jannaschii (also referred to as projannalysin) [3].

1: MALDI-TOF MS and CD spectral analysis for identification and structure prediction of a purified, novel, organic solvent stable, fibrinolytic metalloprotease from Bacillus cereus B80. Saxena R, Singh R; Biomed Res Int. 2015;2015:527015. PMID:25802851

2: Remote homology and the functions of metagenomic dark matter. Lobb B, Kurtz DA, Moreno-Hagelsieb G, Doxey AC; Front Genet. 2015;6:234. PMID:26257768

3: A novel family of soluble minimal scaffolds provides structural insight into the catalytic domains of integral membrane metallopeptidases. Lopez-Pelegrin M, Cerda-Costa N, Martinez-Jimenez F, Cintas-Pedrola A, Canals A, Peinado JR, Marti-Renom MA, Lopez-Otin C, Arolas JL, Gomis-Ruth FX; J Biol Chem. 2013;288:21279-21294. PMID:23733187

4: 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