The pgpA and pgpB genes of Escherichia coli are not essential: evidence for a third phosphatidylglycerophosphate phosphatase

Abstract

To further define the genes and gene products responsible for the in vivo conversion of phosphatidylglycerophosphate to phosphatidylglycerol in Escherichia coli, we disrupted two genes (pgpA and pgpB) which had previously been shown to encode gene products which carried out this reaction in vitro (T. Icho and C. R. H. Raetz, J. Bacteriol. 153:722-730, 1983). Strains with either gene or both genes disrupted had the same properties as the original mutants isolated with mutations in these genes, i.e., reduced in vitro phospholipid phosphatase activities, normal growth properties, and an increase in the level of phosphatidylglycerophosphate (1.6% versus <0.1% in wild-type strains). These results demonstrate that these genes are not required for either normal cell growth or the biosynthesis of phosphatidylglycerol in vivo. In addition, the total phosphatidylglycerophosphate phosphatase activity in the doubly disrupted mutant was reduced by only 50%, which indicates that there is at least one other gene that encodes such an activity and thus accounts for the lack of a dramatic effect on the biosynthesis of anionic phospholipids in these mutant strains. The phosphatidic acid and lysophosphatidic acid phosphatase activities of the pgpB gene product were also significantly reduced in gene-interrupted mutants, but the detection of residual phosphatase activities in these mutants indicated that additional genes encoding such phosphatases exist. The lack of a significant phenotype resulting from disruption of the pgpA and pgpB genes indicates that these genes may be required only for nonessential cell function and leaves the biosynthesis of phosphatidylglycerophosphate as the only step in E. coli phospholipid biosynthesis for which a gene locus has not been identified.Phosphatidylglycerol (PG) is a multifunctional phospholipid in Escherichia coli (30). As the major anionic membrane phospholipid, PG makes up roughly 20% of the total phospholipid in actively growing cells and is turned over to a significant extent in vivo. PG serves as a precursor for a variety of cellular metabolites, including cardiolipin (14), several outer membrane lipoproteins (see reference 11 for a list of references) including the major murein lipoprotein (5), and membrane-derived oligosaccharides (36). It is also a critical component in the SecA-dependent translocation of proteins across the cytoplasmic membrane (21,22). PG is synthesized from CDP-diacylglycerol in two steps. Phosphatidylglycerophosphate (PGP) is first synthesized by transfer of the phosphatidyl backbone from CDP-diacylglycerol to sn-glycerol-3-phosphate (19). PGP is then rapidly dephosphorylated by PGP phosphatase (PGP-tase) to produce PG. Under normal circumstances PGP does not accumulate, which suggests that the regulation of acidic phospholipid biosynthesis occurs before the phosphatase step (18). Our laboratory has previously shown that the gene (pgsA) encoding PGP synthase is essential, thus establishing that acidic phospholipids are necessary for cell growth (12). As a consequ...

Comparative genomics and evolution of eukaryotic phospholipid biosynthesis

“…coli has a second enzyme that participates in PGP dephosphorylation determined as PgpA [57]. Moreover, genetic experiments strongly support the existence of a third E. coli gene that catalyzes the dephosphorylation of PGP [58]. Although PgpA and PgpB enzymes catalyze the same reaction they have no sequence similarity: PgpA homologues are restricted to bacteria whereas PgpB belongs to the universal PAP2 family of enzymes.…”

Understanding phospholipid function: Why are there so many lipids?

“…However, double mutants still carried out PG and CL synthesis. We established that a third gene, pgpC, was responsible for anionic phospholipid biosynthesis (36). Chris later cloned pgpC and characterized mutants and the gene product (37).…”

Conservation of the PTEN catalytic motif in the bacterial undecaprenyl pyrophosphate phosphatase, BacA/UppP

“…The E. coli pgpB gene product was first proposed as one of three phosphatidylglycerol phosphate (PGP) phosphatases critical in the generation of phosphatidylglycerol (Dillon et al, 1996;Funk et al, 1992;Lu et al, 2011). Interestingly, bacteria with disruption of all three PGP phosphatase genes, pgpA, pgpB and pgpC (Lu et al, 2011), are not viable.…”