Lipopolysaccharides of polymyxin B-resistant mutants of Escherichia coli are extensively substituted by 2-aminoethyl pyrophosphate and contain aminoarabinose in lipid A.
Lipopolysaccharides (LPS) of two polymyxin-resistant (pmr) mutants and the corresponding parent strain of Escherichia coli were chemically analysed for composition and subjected to 31P-NMR (nuclear magnetic resonance) for assessment of phosphate substitution. Whereas the saccharide portions, fatty acids, and phosphate contents were similar in wild-type and pmr LPS, the latter contained two- to threefold higher amounts of 2-aminoethanol. The pmr LPS also contained 4-amino-4-deoxy-L-arabinopyranose (L-Arap4N), which is normally not a component of E. coli LPS. This aminopentose has been assigned to be linked to the 4'-phosphate of lipid A. Comparative 31P-NMR analysis of the de-O-acylated LPS of the wild-type and pmr strains revealed that phosphate groups of the pmr LPS were mainly (71-79%) diphosphate diesters, which accounted for only 20% in the wild-type LPS. Diphosphate monoesters were virtually nonexistent in the pmr LPS, whereas they accounted for 42% of all phosphates in wild-type LPS. In the lipid A of the pmr strains, the 4'-phosphate was to a significant degree (35%) substituted by L-Arap4N, whereas in the wild-type LPS the L-ArapN was absent. In the pmr lipid A, 2-aminoethanol was completely substituting the glycosidic pyrophosphate but not the glycosidic monophosphate, forming a diphosphate diester linkage at this position in 40% of lipid A molecules. In the wild-type LPS the glycosidic position of lipid A carried mostly unsubstituted monophosphate and pyrophosphate. Thus the polymyxin resistance was shown to be associated, along with the esterification of the lipid A 4'-monophosphate by aminoarabinose, with extensive esterification of diphosphates in LPS by 2-aminoethanol.
Nummila
K
K
Department of Bacterial Vaccine Research and Molecular Biology, National Public Health Institute, Helsinki, Finland.
Kilpeläinen
I
I
Zähringer
U
U
Vaara
M
M
Helander
I M
IM
D000606:Amino Sugars / Q000302:isolation & purification; D001089:Arabinose / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D011756:Diphosphates / Q000737:chemistry / Q000378:metabolism; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019856:Ethanolamine; D004983:Ethanolamines / Q000737:chemistry / Q000378:metabolism; D008050:Lipid A / Q000737:chemistry* / Q000378:metabolism; D008070:Lipopolysaccharides / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D009154:Mutation; D010710:Phosphates / Q000737:chemistry / Q000378:metabolism; D011112:Polymyxin B / Q000494:pharmacology*
D000606:Amino Sugars; D011756:Diphosphates; D004983:Ethanolamines; D008050:Lipid A; D008070:Lipopolysaccharides; D010710:Phosphates; C016982:aminoarabinose; C040134:4-amino-4-deoxyarabinose; D019856:Ethanolamine; D001089:Arabinose; D011112:Polymyxin B