STUDY OF NEISSERIA MENINGITIDIS LIPOOLIGOSACCHARIDE

脑膜炎双球菌脑膜炎仍然是世界范围内的一个重大健康问题。脑膜炎奈瑟菌的脂寡糖(LOS)是其外膜的主要成分，也是其主要毒力因子。已有研究表明，LOS的寡糖链模仿红细胞和其他组织表面的人类糖鞘糖脂抗原。脑膜炎奈瑟菌的LOS表达也存在时相变化，这与细菌感染的发病机制有关。首次在淋病奈瑟菌中发现了编码糖基转移酶的LGT基因，并对126E(L1)、MC58(L3)和Z2491三株脑膜炎奈瑟菌的LGT同源基因进行了测序。到目前为止，还没有关于脑膜炎奈瑟氏菌其他9种免疫类型的LGT基因座的序列信息。 在两株脑膜炎奈瑟菌M978和A1中，观察到L8-LOS免疫型表达的时相变化和稳定性。为了了解这两个菌株的阶段变异和稳定性的遗传基础，我们从这两个菌株的PCR产物中测定了LGT基因座的核苷酸序列。通过与数据库中脑膜炎奈瑟氏菌和淋病奈瑟菌的LGT序列比较，在这两个菌株中鉴定出两个新的遗传组织。菌株M978含有5个与lgtC、A、B、E同源的开放阅读框，5‘端有一个由部分lgtA和lgtB组成的嵌合ORF，而菌株A1只含有lgtA和lgtE两个基因。这些数据表明，LGT的遗传成分和排列是决定相变和相稳定性的重要因素之一。其他9种免疫类型的LGT基因座的DNA测序已经完成，目前正在对序列进行评估。进一步的工作是从疫苗候选菌株OP-构建htrB突变体，OP-是脑膜炎奈瑟菌M986-NCV的截短LOS突变体，通过从脂质A中去除两种脂肪酸来降低LOS的毒性。

Meningococcal meningitis remains a significant health problem worldwide. The lipooligosaccharide (LOS) of N. meningitidis is a major component of the outer membrane and a major virulence factor. It has been shown that the oligosaccharide chain of LOS mimics human glycosphingolipid antigen on the surfaces of erythrocytes and other tissues. LOS expression in N. meningitidis is also subject to phase variation, which is related to the pathogenesis during the bacterial infection. A genetic locus called lgt encoding glycosyltransferase, responsible for the biosynthesis of oligosaccharide chain, was first identified in Neisseria gonorrhoeae and the lgt homologues have been sequenced for three strains of N. meningitidis, 126E (L1), MC58 (L3) and Z2491. No sequence information on the lgt locus is available for the other 9 immunotypes of N. meningitidis so far. Phase variation and stability in the expression of L8-LOS immunotype was observed in two N. meningitidis strains, M978 and A1. In order to understand the genetic basis of phase variation and stability, we have determined the nucleotide sequences of lgt locus from PCR products for theses two strains. Two novel genetic organizations have been identified in these two strains by comparing them to the lgt sequences of N. meningitidis and N. gonorrhoeae in the databases. Strain M978 contains 5 open reading frames that had homology to lgtC, A, B, E and a mosaic ORF consisted of the partial lgtA and lgtB at the 5'-end, whereas stain A1 contain only two genes included lgtA and lgtE. The data demonstrated that the lgt genetic components and arrangement is one of the important factors to determine phase variation and phase stability. DNA sequencing of lgt loci for other 9 immunotypes have been finished and the sequences are currently being evaluated. The further work is to construct a htrB mutant from a vaccine candidate strain OP-, a truncated LOS mutant of N. meningitidis M986-NCV, to reduce the toxicity of the LOS by removing two of fatty acids from lipid A.