Abstract
Diacylglycerol kinases (DagKs) are key enzymes in lipid metabolism that function to reintroduce diacylglycerol formed from the hydrolysis of phospholipids into the biosynthetic pathway. Bacillus subtilis is a prototypical Gram-positive bacterium with a lipoteichoic acid structure containing repeating units of sn-glycerol-1-P groups derived from phosphatidylglycerol head groups. The B. subtilis homolog of the prokaryotic DagK gene family (dgkA; Pfam01219) was not a DagK but rather was an undecaprenol kinase. The three members of the soluble DagK protein family (Pfam00781) in B. subtilis were tested by complementation of an E. coli dgkA mutant, and only the essential yerQ gene possessed DagK activity. This gene was dubbed dgkB, and the soluble protein product was purified, and its DagK activity was verified in vitro. Conditional inactivation of dgkB led to the accumulation of diacylglycerol and the cessation of lipoteichoic acid formation in B. subtilis. This study identifies a soluble protein encoded by the dgkB (yerQ) gene as an essential kinase in the diacylglycerol cycle that drives lipoteichoic acid production.
Highlights
PtdGro by DgkA [4]
DgkA is an essential gene in cells growing in an osmotically challenging environment, and lethality is induced in DagK gene family (dgkA) mutants by including arbutin in the medium, which acts as an artificial sugar acceptor of glycerol-P groups from PtdGro [11, 12]
Because B. subtilis has a homolog of the E. coli dgkA gene, it has been assumed that the product of this gene is the Diacylglycerol kinases (DagKs) that carries out this function; dgkA is not an essential gene in B. subtilis [21]
Summary
DgkA was dispensable was somewhat surprising and stimulated our investigation of phospholipid turnover in B. subtilis. This work shows that the B. subtilis dgkA gene does not encode a DagK but rather is an undecaprenol kinase (UdpK). The authentic DagK is identified as the product of the essential yerQ (dgkB) gene that encodes a soluble DagK belonging to the eukaryotic DagK protein superfamily (Pfam00781). DgkB is directly tied to the recycling of DAG in vivo (Fig. 1) based on the analysis of lipid metabolism and LTA formation in a conditional dgkB (yerQ) knock-out strain
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