Characterization of the physiological substrate for lipopolysaccharide heptosyltransferases I and II

L-Glycero-D-manno-heptopyranose is a characteristic compound of many lipopo lysaccharide (LPS) core structures of Gram-negative bacteria. In Escherichi a coli two heptosyltransferases, namely WaaC and WaaF, are known to transfe r L-glycero-D-manno-heptopyranose to Re-LPS and Rd(2)-LPS, respectively. It had been proposed that both reactions involve ADPL-glycero-D-manno-heptose as a sugar donor; however, the structure of this nucleotide sugar had neve r been completely elucidated. In the present study, ADPL-glycero-D-manno-he ptose was isolated from a heptosyltransferase-deficient E. coli mutant. and its structure was determined by nuclear magnetic resonance spectroscopy an d matrix-assisted laser-desorption/ionization time-of-flight mass spectrome try as ADPL-glycero-beta -D-manno-heptopyranose. This compound represented the sole constituent of the bacterial extract that was accepted as a sugar donor by heptosyltransferases I and II in vitro.