9.B.261. The Phospho-Glycerol/Phospho-Glycerate Transferase (PGT) Family
Phosphoglycerol transferase I, MdoB, OpgO or YjjO, an enzyme of the inner, cytoplasmic membrane of E. coli, catalyzes the transfer of phosphoglycerol residues from phosphatidylglycerol to membrane-derived oligosaccharides. The products are a phosphoglycerol diester derivative of membrane-derived oligosaccharides and sn-1,2-diglyceride. This enzyme has its active site on the outer surface of the inner membrane. A mutant makes membrane-derived oligosaccharides devoid of phosphoglycerol residues (Jackson et al. 1984).
Membrane-derived oligosaccharides (MDOs) may comprise up to 7% of the cells dry weight. The biosynthesis of MDO is osmoregulated and linked to the metabolism of phospholipids. This leads to substitution of MDO with sn-1-phosphoglycerol and phosphoethanolamine. MDOs also contain succinate in O-ester linkage. The ethanolamine content of MDOs isolated from a mdoB mutant strain is elevated, whereas the number of succinate residues is not affected. The only phenotype of mdoB mutants is a dramatic reduction of the diglyceride content (Fiedler and Rotering 1985).