Putative catalytic domain, repeat 2, of vertebrate phospholipase PLD4
Putative catalytic domain, repeat 2, of vertebrate phospholipases D4 (PLD4, EC 3.1.4.4), homologs of the vaccinia virus protein K4 which is encoded by the HindIII K4L gene. 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), PLD4 has been assigned to PLD superfamily although no catalytic activity has been detected to date. Unlike PLD1 and PLD2, PLD4 does not contain Phox (PX) and Pleckstrin homology (PH) domains but has a putative transmembrane domain. Like other vertebrate homologs of protein K4, PLD4 might be associated with Golgi membranes and alter their lipid content by selectively hydrolyze phosphatidylcholine (PC) into 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.",