This entry represents a group of metalloproteases. The tertiary structure of the Escherichia coli TdlD/TdlE complex has been solved, and shows that the TdlD subunit is the active peptidase, binding a single zinc ion at an HEXXXH motif in which the glutamic acid is a substrate-binding residue and the two histidines are zinc ligands. The third zinc ligand is a cysteine, C-terminal to the HEXXXH motif. The TldE (also known as PmbA) by itself has no catalytic activity, does not bind zinc, and does not carry the HEXXXH motif [1]. TldD and TldE were originally identified as regulators of DNA gyrase. Later, they are shown to be metalloproteases involved in CcdA degradation [2-3].

1: The Origins of Specificity in the Microcin-Processing Protease TldD/E. Ghilarov D, Serebryakova M, Stevenson CEM, Hearnshaw SJ, Volkov DS, Maxwell A, Lawson DM, Severinov K; Structure. 2017;25:1549-1561. PMID:28943336

2: An archaeal protein evolutionarily conserved in prokaryotes is a zinc-dependent metalloprotease. Hu Y, Peng N, Han W, Mei Y, Chen Z, Feng X, Liang YX, She Q; Biosci Rep. 2012;32:609-618. PMID:22950735

3: The highly conserved TldD and TldE proteins of Escherichia coli are involved in microcin B17 processing and in CcdA degradation. Allali N, Afif H, Couturier M, Van Melderen L; J Bacteriol. 2002;184:3224-3231. PMID:12029038