Putative catalytic domain, repeat 2, of vertebrate phospholipase PLD3
Putative catalytic domain, repeat 2, of phospholipase D3 (PLD3, EC 3.1.4.4). The human protein is also known as Hu-K4 or HUK4 and it was identified as a human homolog of the vaccinia virus protein K4, which is encoded by the HindIII K4L gene. PLD3 is found in many human organs with highest expression levels found in the central nervous system. Due to the presence of two copies of the conserved HKD motif (H-x-K-x(4)-D, where x represents any amino acid residue), PLD3 has been assigned to the PLD superfamily although no catalytic activity has been detected experimentally. PLD3 is a membrane-bound protein that colocalizes with protein disulfide isomerase, an endoplasmic reticulum (ER) protein. Like other homologs of protein K4, PLD3 might alter the lipid content of associated membranes by selectively hydrolyzing phosphatidylcholine (PC) into the corresponding phosphatidic acid, which is thought to be involved in the regulation of lipid movement.
Comment:Based on similarity with Streptomyces sp. phospholipase D, which functions as a bi-lobed monomer with two catalytic domains. Each domain carries one copy of the conserved HKD motif and two domains form a single active site.
Comment:The HKD signature motif (expanded to H-x-K-x(4)-D-x(6)-G-T-x-N in this subfamily, where x represents any amino acid residue) characterizes the PLD superfamily.
Comment:Most residues in the HKD motif are part of the active site.
Jiyao W et al.(2023). "The conserved domain database in 2023.",