Structure and biosynthesis of free lipid A molecules that replace lipopolysaccharide in Francisella tularensis subsp novicida
Structure and biosynthesis of free lipid A molecules that replace lipopolysaccharide in Francisella tularensis subsp novicida
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DOI：
10.1021/bi061767s
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发表时间：
2006-12-05
期刊：
影响因子：
2.9
通讯作者：
Raetz, Christian R. H.
中科院分区：
文献类型：
--
作者：
Wang, Xiaoyuan;Ribeiro, Anthony A.;Raetz, Christian R. H.
土拉热弗朗西斯菌亚种novicidaU 112磷脂是未经水解而提取的，主要由磷脂酰乙醇胺、磷脂酰甘油、磷脂酰胆碱和两种脂质A物质（命名为A1和A2）组成。这些脂质A物质以7：1的比例存在，占总磷脂的15%，如通过32 Pi标记所判断的。虽然在F.土拉热亚种novicida U112，不到5%的总脂质A共价连接到它。A1和A2通过电喷雾电离和基质辅助激光解吸电离质谱，气相色谱/质谱和NMR光谱分析。这两种化合物都是葡糖胺的二糖，在2、3和2'位被一级3-羟基硬脂酰链酰化，在2'位被二级棕榈酰残基酰化。还存在少量同量异位物质和一些含有3-羟基棕榈酰基链代替3-羟基硬脂酸酯的脂质A分子。A1和A2的4 '-和3'-位置未衍生化，并且3-脱氧-D-甘露-辛酮糖酸（Kdo）不可检测。如NMR光谱和气相色谱/质谱所示，A1和A2的1-磷酸基团均被α-连接的半乳糖胺残基修饰。α-连接的葡萄糖部分连接至A2的6 '-位。F.土拉热亚种杀novicida脂多糖仅由组分A1组成。F.土拉热亚种缺乏arnT基因的杀线虫突变体在其脂质A上不含半乳糖胺残基。F.土拉热亚种novicida可能是由一个不寻常的Kdo水解酶存在于这种生物体的膜启动。
Francisella tularensis subsp. novicida U112 phospholipids, extracted without hydrolysis, consist mainly of phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, and two lipid A species, designated A1 and A2. These lipid A species, present in a ratio of 7: 1, comprise 15% of the total phospholipids, as judged by 32Pi labeling. Although lipopolysaccharide is detectable in F. tularensis subsp. novicida U112, less than 5% of the total lipid A is covalently linked to it. A1 and A2 were analyzed by electrospray ionization and matrix-assisted laser desorption ionization mass spectrometry, gas chromatography/ mass spectrometry, and NMR spectroscopy. Both compounds are disaccharides of glucosamine, acylated with primary 3-hydroxystearoyl chains at positions 2, 3, and 2' and a secondary palmitoyl residue at position 2'. Minor isobaric species and some lipid A molecules containing a 3-hydroxypalmitoyl chain in place of 3-hydroxystearate are also present. The 4'- and 3'-positions of A1 and A2 are not derivatized, and 3-deoxy-D-manno-octulosonic acid (Kdo) is not detectable. The 1-phosphate groups of both A1 and A2 are modified with an alpha-linked galactosamine residue, as shown by NMR spectroscopy and gas chromatography/ mass spectrometry. An alpha-linked glucose moiety is attached to the 6'- position of A2. The lipid A released by mild acid hydrolysis of F. tularensis subsp. novicida lipopolysaccharide consists solely of component A1. F. tularensis subsp. novicida mutants lacking the arnT gene do not contain a galactosamine residue on their lipid A. Formation of free lipid A in F. tularensis subsp. novicida might be initiated by an unusual Kdo hydrolase present in the membranes of this organism.