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Putative catalytic domain, repeat 2, of Yersinia pestis murine toxin-like proteins Putative catalytic domain, repeat 2, of Yersinia pestis murine toxin (Ymt), a plasmid-encoded phospholipase D (PLD, EC 3.1.4.4), and similar proteins. Ymt is important in order for Yersinia pestis to survive and spread. It is toxic to mice and rats but not to other animals. It is not a conventional secreted exotoxin, but a cytoplasmic protein that is released upon bacterial lysis. Ymt may be active as a dimer. The monomeric Ymt consists of two catalytic domains, each of which contains one copy of the conserved HKD motif (H-x-K-x(4)-D, where x represents any amino acid residue). Two HKD motifs from two domains form a single active site. Ymt has PLD-like activity and has been classified into the PLD superfamily. It hydrolyzes the terminal phosphodiester bond in several phospholipids, with preference for phosphatidylethanolamine (PE) over phosphatidylcholine (PC) and phosphatidylserine (PS). Like other PLD enzymes, Ymt may utilize a common two-step ping-pong catalytic mechanism involving an enzyme-substrate intermediate to cleave phosphodiester bonds. The two histidine residues from the two HKD motifs play key roles in the catalysis. Upon substrate binding, a histidine residue from one HKD motif could function as the nucleophile, attacking the phosphodiester bond to create a covalent phosphohistidine intermediate, while the other histidine residue from the second HKD motif could serve as a general acid, stabilizing the leaving group. In terms of sequence similarity, Ymt is closely related to Streptomyces PLDs. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",