Moran A P, Lindner B, Walsh E J
Department of Microbiology, University College, Galway, Ireland.
J Bacteriol. 1997 Oct;179(20):6453-63. doi: 10.1128/jb.179.20.6453-6463.1997.
The chemical structure of free lipid A isolated from rough- and smooth-form lipopolysaccharides (R-LPS and S-LPS, respectively) of the human gastroduodenal pathogen Helicobacter pylori was elucidated by compositional and degradative analysis, nuclear magnetic resonance spectroscopy, and mass spectrometry. The predominant molecular species in both lipid A components are identical and tetraacylated, but a second molecular species which is hexaacylated is also present in lipid A from S-LPS. Despite differences in substitution by acyl chains, the hydrophilic backbone of the molecules consisted of beta(1,6)-linked D-glucosamine (GlcN) disaccharide 1-phosphate. Because of microheterogeneity, nonstoichiometric amounts of ethanolamine-phosphate were also linked to the glycosidic hydroxyl group. In S-LPS, but not in R-LPS, the hydroxyl group at position 4' was partially substituted by another phosphate group. Considerable variation in the distribution of fatty acids on the lipid A backbone was revealed by laser desorption mass spectrometry. In tetraacyl lipid A, the amino group of the reducing GlcN carried (R)-3-hydroxyoctadecanoic acid (position 2), that of the nonreducing GlcN carried (R)-3-(octadecanoyloxy)octadecanoic acid (position 2'), and ester-bound (R)-3-hydroxyhexadecanoic acid was attached at position 3. Hexaacyl lipid A had a similar substitution by fatty acids, but in addition, ester-bound (R)-3-(dodecanoyloxy)hexadecanoic acid or (R)-3(tetradecanoyloxy)hexadecanoic acid was attached at position 3'. The predominant absence of ester-bound 4'-phosphate and the presence of tetraacyl lipid A with fatty acids of 16 to 18 carbons in length differentiate H. pylori lipid A from that of other bacterial species and help explain the low endotoxic and biological activities of H. pylori LPS.
通过组成和降解分析、核磁共振光谱法以及质谱法，阐明了从人胃十二指肠病原体幽门螺杆菌的粗糙型和光滑型脂多糖（分别为R-LPS和S-LPS）中分离出的游离脂质A的化学结构。两种脂质A成分中的主要分子种类相同，均为四酰化，但六酰化的第二种分子种类也存在于S-LPS的脂质A中。尽管酰基链的取代存在差异，但分子的亲水性主链由β(1,6)-连接的D-葡萄糖胺（GlcN）二糖1-磷酸组成。由于微不均一性，非化学计量的磷酸乙醇胺也与糖苷羟基相连。在S-LPS中，而非R-LPS中，4'位的羟基部分被另一个磷酸基团取代。激光解吸质谱法揭示了脂质A主链上脂肪酸分布的显著差异。在四酰化脂质A中，还原型GlcN的氨基携带(R)-3-羟基十八烷酸（位置2），非还原型GlcN的氨基携带(R)-3-(十八烷酰氧基)十八烷酸（位置2'），酯键连接的(R)-3-羟基十六烷酸连接在位置3。六酰化脂质A具有类似的脂肪酸取代，但此外，酯键连接的(R)-3-(十二烷酰氧基)十六烷酸或(R)-3-(十四烷酰氧基)十六烷酸连接在位置3'。酯键连接的4'-磷酸的主要缺失以及存在长度为16至18个碳的脂肪酸的四酰化脂质A，使幽门螺杆菌脂质A与其他细菌种类的脂质A不同，并有助于解释幽门螺杆菌LPS的低内毒素和生物活性。
