Regulation of the synthesis of membrane-derived oligosaccharides in Escherichia coli. Assay of phosphoglycerol transferase I in vivo.
Membrane-derived oligosaccharides are periplasmic constituents of Escherchia coli and other Gram-negative bacteria. Oligosaccharides in this family may be variously substituted with O-succinyl ester residues, and with sn-1-phosphoglycerol and phosphoethanolamine residues derived from membrane phospholipids. Membrane-derived oligosaccharides appear to be important in osmoregulation, because their synthesis is under strict control (Kennedy, E.P. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 1092-1095). Maximum rate of synthesis is at very low osmolarity of the medium. Phosphoglycerol residues are transferred from phosphatidylglycerol to membrane-derived oligosaccharides, or to certain beta-glucoside acceptors, in a reaction catalyzed by phosphoglycerol transferase I, an enzyme of the inner membrane (Jackson, B. J., and Kennedy, E.P. (1983) J. Biol. Chem. 258, 2394-2398). We now report that this enzyme catalyzes the transfer of phosphoglycerol residues to arbutin (p-hydroxyphenyl-beta-D-glucoside) added to the medium with Km similar to that observed with the cell-free enzyme. The active site of the enzyme must therefore be on the periplasmic face of the inner membrane. We assayed phosphoglycerol transferase I in vivo and found that it is present and completely active even in cells growing in medium of very high osmolarity, in which the synthesis of membrane-derived oligosaccharides is severely reduced. We conclude that osmotic regulation must occur at the stage of the synthesis of oligosaccharide chains. A study of the kinetics of transfer of phosphoglycerol residues to membrane-derived oligosaccharides in vivo revealed that synthesis of the polyglucose chains must stop abruptly upon transfer of cells from medium of low to high osmolarity, inconsistent with a model postulating simple dilution of some rate-limiting enzyme during growth at the higher osmolarity.
D001104:Arbutin / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology; D004926:Escherichia coli / Q000201:enzymology*; D005990:Glycerol / Q000378:metabolism; D007700:Kinetics; D009844:Oligosaccharides / Q000096:biosynthesis*; D009994:Osmolar Concentration; D010770:Phosphotransferases / Q000378:metabolism*; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*; D017855:Transferases (Other Substituted Phosphate Groups)
D009844:Oligosaccharides; D011135:Polysaccharides, Bacterial; D001104:Arbutin; D010770:Phosphotransferases; D017855:Transferases (Other Substituted Phosphate Groups); C037247:phosphatidylglycerol - membrane-oligosaccharide glycerophosphotransferase; D005990:Glycerol