Robertson B D, Frosch M, van Putten J P
Max-Planck-Institut für Biologie, Abteilung Infektionsbiologie, Tübingen, Germany.
J Bacteriol. 1994 Nov;176(22):6915-20. doi: 10.1128/jb.176.22.6915-6920.1994.
Neisseria gonorrhoeae synthesizes a rough lipopolysaccharide that does not contain any of the repetitive units characteristic of the smooth lipopolysaccharide of members of the family Enterobacteriaceae. Three gonococcal homologs of Salmonella serovar typhimurium genes involved in the synthesis of the rhamnose component of the repetitive subunits have been isolated. Gonococcal homologs for rfbB, rfbA, and rfbD were found downstream of the galE gene in a region of the chromosome which shows overall homology with the meningococcal capsule gene complex region D. Sequence alignment demonstrated that the gonococcal gene products have 69, 65, and 54% amino acid identity with the Salmonella proteins RfbB, RfbA, and RfbD. The gonococcal RfbB and RfbA amino acid sequences share even more identical residues (73 and 65%, respectively) with the amino acid sequences derived from Escherichia coli genes o355 and o292, respectively. These genes are clustered with the genes involved in the biosynthesis of enterobacterial common antigen, and o355 is listed in the GenBank and Swiss Protein data banks as rffE (encoding UDP-GlcNAc-2-epimerase). However, complementation studies demonstrated that o355 does not encode the enzyme UDP-GlcNAc-2-epimerase. Gonococcal strains constructed with null mutations in the rfbBAD genes were unchanged in lipopolysaccharide phenotype and in the synthesis of gonococcal carbohydrate-containing C antigen. We were unable to detect any changes in gonococcal phenotype with respect to lipopolysaccharide sialylation, monoclonal-antibody binding, serum sensitivity, or interaction with eukaryotic cells in vitro. We conclude that the absence of a homolog for rfbC precludes the existence of a functional dTDP-rhamnose biosynthesis pathway in the gonococcal strains examined and that these genes are only maintained in N. gonorrhoeae either because of the presence of the galE gene or because of another as yet unrecognized function.
淋病奈瑟菌合成一种粗糙型脂多糖，该脂多糖不包含肠杆菌科成员光滑型脂多糖所特有的任何重复单元。已分离出鼠伤寒沙门氏菌血清型中参与重复亚基鼠李糖成分合成的三个基因的淋病奈瑟菌同源物。在染色体的一个区域中，发现淋病奈瑟菌rfbB、rfbA和rfbD的同源物位于galE基因下游，该区域与脑膜炎奈瑟菌荚膜基因复合体区域D总体同源。序列比对表明，淋病奈瑟菌基因产物与沙门氏菌蛋白RfbB、RfbA和RfbD的氨基酸同一性分别为69%、65%和54%。淋病奈瑟菌的RfbB和RfbA氨基酸序列与分别源自大肠杆菌基因o355和o292的氨基酸序列具有更多相同残基（分别为73%和65%）。这些基因与参与肠杆菌共同抗原生物合成的基因聚集在一起，o355在GenBank和瑞士蛋白质数据库中列为rffE（编码UDP-GlcNAc-2-表异构酶）。然而，互补研究表明o355不编码UDP-GlcNAc-2-表异构酶。在rfbBAD基因中构建了无效突变的淋病奈瑟菌菌株，其脂多糖表型和含淋病奈瑟菌碳水化合物的C抗原合成未发生变化。我们在体外未检测到淋病奈瑟菌在脂多糖唾液酸化、单克隆抗体结合、血清敏感性或与真核细胞相互作用方面的任何表型变化。我们得出结论，在所检测的淋病奈瑟菌菌株中，缺乏rfbC同源物排除了功能性dTDP-鼠李糖生物合成途径的存在，并且这些基因仅在淋病奈瑟菌中得以保留，要么是因为galE基因的存在，要么是因为另一种尚未被认识的功能。
