Structure and biosynthesis of free lipid A molecules that replace lipopolysaccharide in Francisella tularensis subsp novicida

被引:100
作者
Wang, Xiaoyuan
Ribeiro, Anthony A.
Guan, Ziqiang
McGrath, Sara C.
Cotter, Robert J.
Raetz, Christian R. H. [1 ]
机构
[1] Duke Univ, Med Ctr, Dept Biochem, Durham, NC 27710 USA
[2] Duke Univ, Med Ctr, Duke NMR Spect Ctr, Durham, NC 27710 USA
[3] Duke Univ, Med Ctr, Dept Radiol, Durham, NC 27710 USA
[4] Johns Hopkins Univ, Sch Med, Dept Pharmacol & Mol Sci, Baltimore, MD 21205 USA
关键词
D O I
10.1021/bi061767s
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
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.
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页码:14427 / 14440
页数:14
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