Study on the transport of the Opolysaccharide in Escherichia

革兰氏阴性菌的O-多糖具有结构多态，因此它们被用作血清学分型的O-抗原。O多糖是脂多糖(LPS)的一部分，通过核心-寡糖部分与脂类A共价结合。大肠杆菌O9a菌株F719的Wb*基因簇由8个基因组成，其中2个与GDP-甘露糖合成有关，2个与ABC转运蛋白相关，3个与甘露糖转移酶相关，1个功能未知。利用突变的质粒和互补试验对wbdD基因进行功能研究。Tn1000插入的质粒合成了O9a多糖，但它们没有转运到细胞表面，而是在细胞质中发现。用抗O9a多糖的单抗进行的电子显微镜分析证实了这种多糖的分布。克隆的wbdD基因补充了突变，但当克隆的基因在lac启动子的控制下过表达时，合成的O多糖长度变短。根据这些结果，可能存在除由该簇中的基因所揭示的ABC运输系统之外的另一种运输系统。此外，多糖长度的变化表明，新的转运系统可能与合成的O多糖转移到脂多糖的核心低聚糖的时间有关。为了证实这一假设，需要进行更详细的分析。

O polysaccharides of Gram-negative bacteria are structurally polymorphic, and consequently, they are utilized as the O-antigen for serological typing. The O polysaccharide is part of lipopolysaccharides (LPS) and covalently binds to lipid A through the core-oligosaccharide portion. The wb* gene cluster is responsible for the O polysaccharide synthesis.The wb* cluster of Escherichia coll O9a strain F719 is constituted of eight genes, two for GDP-mannose synthesis, two for the putative ABC-transporter, three for mannosyltransferases, and one whose function is unknown. The gene, wbdD, was investigated its function using mutated plasmid and the complementation test. Tn1000 inserted plasmid synthesized the O9a polysaccharides but they did not transport to the cell surface instead found in cell cytoplasm. Electron microscopic analysis using a monoclonal antibody against the O9a polysaccharide confirmed this distribution of the polysaccharides. Cloned wbdD gene complemented the mutation, however, when the cloned gene was over expressed under the control of the lac promoter, the length of the O polysaccharides synthesized became shorter. Based on these results, the possibility was shown that there might be another transport system in addition to the ABC-transport system revealed by the genes in the cluster. Moreover, the change in the polysaccharide length suggested that the novel transport system might be correlated with the timing that the synthesized O polysaccharides are transferred to the core-oligosaccharide of LPS. More detailed analyzes would be necessary to confirm the hypothesis.