Genetics of Neisseria meningitidis lipooligosaccharide

摘要：脑膜炎球菌性脑膜炎仍然是世界范围内的一个重大卫生问题。低脂寡糖（LOS）是脑膜炎奈索菌外膜的主要成分，也是主要的毒力因子。研究表明，LOS的低聚糖链在红细胞和其他组织表面模拟人的鞘糖脂。根据寡糖链结构的抗原变异，将脑膜炎奈索菌的LOS分为L1-L12型。在淋病奈瑟菌中首次发现了编码糖基转移酶的3个染色体位点上的7个轻基因，这些基因负责低聚糖链的生物合成。对3株脑膜炎奈索菌126E （L1）、MC58 （L3）和Z2491 （L9）的轻同源物进行了测序。观察了M978和A1两株脑膜炎奈索菌在不同生长条件下L8-LOS免疫型表达的变化和稳定性。这两个菌株的lgt位点的核苷酸序列已经确定。通过与数据库中脑膜炎奈瑟菌和淋病奈瑟菌的轻序列进行比较，在这两种菌株中发现了两个新的遗传组织。菌株M978含有5个与lgtC、A、B、E同源的ORF和一个由部分lgtA和lgtB组成的镶嵌ORF （lgtZ）。菌株A1只包含两个基因，lgtA和lgtH。结果表明，轻遗传成分和排列是决定脑膜炎奈索菌LOS表达变异和稳定性的重要因素之一。其余9种免疫型的3个轻型基因座的DNA序列也已确定。为了比较，我们还用PCR和DNA杂交的方法检测了非致病性奈瑟菌的lgt基因。基于lgt基因在三个染色体位点上的组成和组织，提出了LOS基因分型方案。对致病性和非致病性奈瑟菌中lgt基因的系统发育关系和进化历史进行了评价。目前正在利用与2001年加拿大魁北克省脑膜炎球菌病暴发有关的血清C组菌株，将LOS基因分型系统应用于流行病学调查。

Summary: 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 glycosphingolipids on the surfaces of erythrocytes and other tissues. The LOS of N. meningitidis was divided into 12 immonotypes (L1-L12) based on antigenic variations in the structure of the oligosaccharide chains. Seven lgt genes at three chromosomal loci encoding glycosyltransferase, responsible for the biosynthesis of oligosaccharide chains, were first identified in Neisseria gonorrhoeae. The lgt homologues have been sequenced for three strains of N. meningitidis, 126E (L1), MC58 (L3) and Z2491 (L9). Variation and stability in expression of the L8-LOS immunotype was observed in two N. meningitidis strains, M978 and A1, under different growth conditions. The nucleotide sequences of the lgt locus for theses two strains have been determined. 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 ORFs that had homology to lgtC, A, B, E and a mosaic ORF (lgtZ) consisting of the partial lgtA and lgtB. Strain A1 contains only two genes, lgtA and lgtH. The data demonstrated that the lgt genetic components and arrangement is one of the important factors to determine variation and stability of expression of N. meningitidis LOS. DNA sequences of three lgt loci for the remaining 9 immunotypes have now been determined as well. For comparison, the lgt genes in nonpathogenic Neisseria species were also detected by PCR and DNA hybridization. A LOS genetic typing scheme was proposed based on the composition and organization of the lgt genes at three chromosomal loci. The phylogenetic relationships and evolutionary history of the lgt genes in pathogenic and nonpathogenic Neisseria species were evaluated. Application of the LOS genetic typing system for the epidemiological investigation is currently being worked on using Serogroup C strains associated with the 2001 meningococcal disease outbreak in Quebec, Canada.