Catalytic domain, repeat 2, of Escherichia coli cardiolipin synthase ybhO and similar proteins
Catalytic domain, repeat 2, of Escherichia coli cardiolipin (CL) synthase ybhO and similar proteins. In Escherichia coli, there are two genes, f413 (ybhO) and o493 (ymdC), which are homologous to gene cls that encodes the Escherichia coli CL synthase. The prototype of this subfamily is Escherichia coli CL synthase ybhO specified by the f413 (ybhO) gene. ybhO is a membrane-bound protein that catalyzes the formation of cardiolipin (CL) by transferring phosphatidyl group between two phosphatidylglycerol molecules. It can also catalyze phosphatidyl group transfer to water to form phosphatidate. In contrast to the Escherichia coli CL synthase encoded by the cls gene (EcCLS), ybhO does not hydrolyze CL. Moreover, ybhO lacks an N-terminal segment encoded by Escherichia coli cls, which makes ybhO easy to denature. The monomer of ybhO consists of two catalytic domains. Each catalytic domain contains one copy of the conserved HKD motif (H-x-K-x(4)-D, where x represents any amino acid residue) that characterizes the phospholipase D (PLD) superfamily. Two HKD motifs from two domains form a single active site involved in phosphatidyl group transfer. ybhO can be stimulated by phosphate and inhibited by CL, the product of the reaction, and by phosphatidate. Phosphate stimulation may be unique to enzymes with CL synthase activity belonging to the PLD superfamily.
Comment:Based on similarity with 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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