Catalytic domain, repeat 2, of eukaryotic phosphatidylglycerophosphate synthases
Catalytic domain, repeat 2, of eukaryotic phosphatidylglycerophosphate (PGP) synthases, also called CDP-diacylglycerol--glycerol-3-phosphate 3-phosphatidyltransferase (EC 2.7.8.5). Eukaryotic PGP synthases are different and unrelated to prokaryotic PGP synthases and yeast phosphatidylserine synthase. They catalyze the synthesis of PGP from CDP-diacylglycerol and sn-glycerol 3-phosphate, the committed and rate-limiting step in the biosynthesis of cardiolipin (CL), which is an essential component of many mitochondrial functions in eukaryotes. Members in this subfamily all have two HKD motifs (H-x-K-x(4)-D, where x represents any amino acid residue) that characterizes the phospholipase D (PLD) superfamily. They may utilize a common two-step ping-pong catalytic mechanism involving a substrate-enzyme intermediate to cleave phosphodiester bonds. The two motifs are suggested to constitute the active site involved in the phosphatidyl group transfer.
Comment:Based on similarity with Haemophilus Influenzae phosphatidylserine synthase, which contains a single active site at the interface of two catalytic domains; each domain contains one HKD motif.
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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