The biosynthesis of membrane-derived oligosaccharides. A membrane-bound phosphoglycerol transferase.

Abstract

Membrane-derived oligosaccharides, found in the Escherichia coli periplasmic space (Schulman, H., and Kennedy, E. P. (1979) J. Bacteriol. 137, 686-688), are composed of 8-10 units of glucose, the sole sugar, in beta 1 leads to 2 and beta 1 leads to 6 linkages (Schneider, J. E., Reinhold, V., Rumley, M. K., and Kennedy, E. P. (1979) J. Biol. Chem. 254, 10135-10138). Oligosaccharides in this family are variously substituted with succinyl ester residues, as well as with sn-1-phosphoglycerol and phosphoethanolamine, both derived from membrane phospholipids. These negatively charged oligosaccharides may function in cellular osmoregulation since their synthesis is under osmotic control (Kennedy, E. P. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 1092-1095). We now report initial characterization of an enzyme catalyzing transfer of phosphoglycerol residues from phosphatidylglycerol to membrane-derived oligosaccharides or to synthetic beta-glucoside acceptors. The products are sn-1,2-diglyceride and beta-glucoside-6-phosphoglycerol. Localized in the inner membrane, the transferase has a requirement for divalent cations, of which manganese is most effective, and a pH optimum of 8.9 in vitro.