Catalytic domain, repeat 2, of uncharacterized bacterial proteins with similarity to vertebrate phospholipases, PLD1 and PLD2
Catalytic domain, repeat 2, of uncharacterized bacterial counterparts of vertebrate, yeast and plant phospholipase D (PLD, EC 3.1.4.4). PLDs hydrolyze the terminal phosphodiester bond of phospholipids with the formation of phosphatidic acid and alcohols. They also catalyze the transphosphatidylation of phospholipids to acceptor alcohols, by which various phospholipids can be synthesized. Instead of the regulatory C2 (calcium-activated lipid binding) domain in plants and the adjacent Phox (PX) and the Pleckstrin homology (PH) N-terminal domains in most mammalian and yeast PLDs, many members in this subfamily contain a SNARE associated C-terminal domain, whose functional role is unclear. Like other PLD enzymes, members in this subfamily contain two copies of the conserved HKD motif (H-x-K-x(4)-D, where x represents any amino acid residue), that may play an important role in the catalysis.
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-S-x-N, where x represents any amino acid residue) characterizes the PLD superfamily.
Comment:Most residues in the HKD motif are part of the active site.
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