Three Phosphatidylglycerol-phosphate Phosphatases in the Inner Membrane of Escherichia coli

Abstract

The phospholipids of Escherichia coli consist mainly of phosphatidylethanolamine, phosphatidylglycerol (PG), and cardiolipin. PG makes up ϳ25% of the cellular phospholipid and is essential for growth in wild-type cells. PG is synthesized on the inner surface of the inner membrane from cytidine diphosphate-diacylglycerol and glycerol 3-phosphate, generating the precursor phosphatidylglycerol-phosphate (PGP). This compound is present at low levels (ϳ0.1% of the total lipid). Dephosphorylation of PGP to PG is catalyzed by several PGPphosphatases. The pgpA and pgpB genes, which encode structurally distinct PGP-phosphatases, were identified previously. Double deletion mutants lacking pgpA and pgpB are viable and still make PG, suggesting the presence of additional phosphatase(s). We have identified a third PGP-phosphatase gene (previously annotated as yfhB but renamed pgpC) using an expression cloning strategy. A mutant with deletions in all three phosphatase genes is not viable unless covered by a plasmid expressing either pgpA, pgpB, or pgpC. When the triple mutant is covered with the temperature-sensitive plasmid pMAK705 expressing any one of the three pgp genes, the cells grow at 30 but not 42°C. As growth slows at 42°C, PGP accumulates to high levels, and the PG content declines. PgpC orthologs are present in many other bacteria.

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

“…Of particular note, based on complete BLAST searches, obvious homologues/orthologues of YbjG and YeiU are not found in Gram-positive bacteria, whilst the PgpB and BacA/UppP proteins are present extensively in the older bacterial phyla. The presence of PgpB across a wide range of eubacteria may be due to its importance as a PGP phosphatase (Lu et al, 2011;Touzé et al, 2008a). The high level of identity for BacA/UppP (63 %) demonstrates clearly the evolutionary pressure to maintain the functionality of this protein and also raises further questions about the biological relevance of the other proteins.…”

“…Also included recently in the PTP-lipid phosphatase family is a class 3 VH1-like DUSP mitochondrial enzyme, PTPMT1, whose preferred substrate is PGP (Tonks, 2013;Xiao et al, 2011;Zhang et al, 2011). Interestingly, PGP also serves as the substrate for the bacterial enzymes, PgpA, PgpB and PgpC (Lu et al, 2011), whilst, as noted previously, PgpB also contains partial undecaprenyl pyrophosphate phosphatase activity (Touzé et al, 2008a). The substrates for PTEN, BacA/UppP and PTPMT1 are shown in Fig.…”

“…Interestingly, bacteria with disruption of all three PGP phosphatase genes, pgpA, pgpB and pgpC (Lu et al, 2011), are not viable. However, Touzé et al (2008a) have argued that PgpB functions as a periplasmic undecaprenyl pyrophosphate phosphatase even though their data demonstrates a 100-fold higher activity towards PGP.…”

“…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.…”

Specific roles of phosphatidylglycerols in hosts and microbes

“…Bacterial pgsA and eukaryotic homologues PGS1 (12;13) encode the enzymes that displace CDP by glycerol-phosphate to provide PG-phosphate, which is further dephosphorylated by a phosphatase to form PG. There are three pgp genes in the E. coli genome (pgpA, pgpB and pgpC), perhaps not all to serve exclusively for PG phosphate hydrolysis (14). In eukaryotes, multiple PG phosphatase genes also exist (15;16), and enzymatic activity has been detected in mitochondria matrix (17).…”