title: Purification and properties of lipid A disaccharide synthase of Escherichia coli.
abstract: Lipid A disaccharide synthase of Escherichia coli catalyzes the reaction 2,3-diacyl-GlcN-1-P + UDP-2,3-diacyl-GlcN----2',3'-diacyl-GlcN (beta,1'----6)2,3-diacyl-GlcN-1-P + UDP (Ray, B. L., Painter, G., and Raetz, C. R. H. (1984) J. Biol. Chem. 259, 4852-4859). Using a strain that overproduces the enzyme about 200-fold we have devised a simple purification to near homogeneity, utilizing two types of dye-ligand resins and heparin-agarose. The overall purification starting with membrane-free extracts was 54-fold (16,000-fold relative to wild-type extracts) with a 31% yield. The subunit molecular mass determined by sodium dodecyl sulfate gel electrophoresis is approximately 42,000 daltons, and the native enzyme appears to be a dimer. The amino-terminal sequence is (X)-(Thr)-Glu-Gln-(X)-Pro-Leu-Thr-Ie-Ala..., consistent with the results predicted from the DNA sequence, Met-Thr-Glu-Gln-Arg-Pro-Leu-Thr-Ile-Ala.... The purified enzyme displays a strong kinetic preference for sugar substrates bearing two fatty acyl moieties, but it is, nevertheless, very useful for the semisynthetic preparation of many lipid A analogs. Gel filtration studies demonstrate that the natural substrates (2,3-diacyl-GlcN-1-P and UDP-2,3-diacyl-GlcN) form micelles (n approximately equal to 300), rather than bilayers, under conditions used to assay the enzyme. Unlike most enzymes of glycerophospholipid synthesis, the lipid A disaccharide synthase does not require the presence of a detergent for catalytic activity. At 1 mM UDP-2,3-diacyl-GlcN the Vmax and Km values for 2,3-diacyl-GlcN-1-P are 14,028 +/- 513 nmol/min/mg and 0.27 +/- 0.02 mM. When 2,3-diacyl-GlcN-1-P is maintained at 1 mM, they are 12,368 +/- 472 nmol/min/mg and 0.11 +/- 0.01 mM for UDP-2,3-diacyl-GlcN.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D005796:Genes; D005798:Genes, Bacterial; D006602:Hexosyltransferases / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D007700:Kinetics; D008050:Lipid A / Q000096:biosynthesis; D008823:Micelles; D015394:Molecular Structure; D009154:Mutation; D017351:N-Acetylglucosaminyltransferases; D013379:Substrate Specificity
chemical_list: D000596:Amino Acids; D008050:Lipid A; D008823:Micelles; D006602:Hexosyltransferases; D017351:N-Acetylglucosaminyltransferases; C050305:lipid A disaccharide synthase