Genetic basis for Rhizobium etli CE3 O-antigen O-methylated residues that vary according to growth conditions.
Genetic basis for Rhizobium etli CE3 O-antigen O-methylated residues that vary according to growth conditions.
复制标题
根瘤菌 CE3 O-抗原 O-甲基化残基的遗传基础根据生长条件而变化。
DOI：
10.1128/jb.01154-09
复制
发表时间：
2010
影响因子：
3.2
通讯作者：
Noel,KDale
中科院分区：
文献类型：
--
作者：
Ojeda,KristyleaJ;Box,JodieM;Noel,KDale
根瘤菌CE 3 O抗原是一种固定长度的杂聚物，O甲基化是糖修饰的主要类型。平均每个完整的O抗原有两个O-甲基化残基：一个重复单元内的多个O-甲基化末端岩藻糖和岩藻糖残基的2-O甲基化。当细菌在宿主植物菜豆或其种子分泌物存在下生长时，甲基化末端岩藻糖的量减少，2-O-甲基岩藻糖的量增加。插入诱变用于鉴定这些O-甲基化残基存在所需的开放阅读框。甲基化末端岩藻糖的存在需要基因wreA、wreB、wreC、wreD和wreF，而内部岩藻糖的2-O甲基化需要双功能基因wreM的甲基转移酶结构域。仅缺乏甲基化末端岩藻糖、仅缺乏2-O甲基化或同时缺乏甲基化末端岩藻糖和2-O甲基化的突变体没有表现出其他脂多糖结构缺陷。因此，正常的O-抗原长度、运输或组装成最终的脂多糖都不需要这些修饰。这与某些肠道细菌形成鲜明对比，其中末端装饰的缺乏严重影响O抗原长度和转运。R.在与寄主菜豆的共生过程中，只缺乏甲基化末端岩藻糖的突变体没有改变，而只缺乏2-O-甲基岩藻糖的突变体在共生过程中表现出根瘤发育的延迟。这些结果支持了先前的结论，甲基化的终端岩藻糖是共生的，而2-O甲基化的内部岩藻糖以某种方式促进共生的早期事件。
TheRhizobium etliCE3 O antigen is a fixed-length heteropolymer with O methylation being the predominant type of sugar modification. There are two O-methylated residues that occur, on average, once per complete O antigen: a multiply O-methylated terminal fucose and 2-O methylation of a fucose residue within a repeating unit. The amount of the methylated terminal fucose decreases and the amount of 2-O-methylfucose increases when bacteria are grown in the presence of the host plant,Phaseolus vulgaris, or its seed exudates. Insertion mutagenesis was used to identify open reading frames required for the presence of these O-methylated residues. The presence of the methylated terminal fucose required geneswreA,wreB,wreC,wreD, andwreF, whereas 2-O methylation of internal fucoses required the methyltransferase domain of bifunctional genewreM. Mutants lacking only the methylated terminal fucose, lacking only 2-O methylation, or lacking both the methylated terminal fucose and 2-O methylation exhibited no other lipopolysaccharide structural defects. Thus, neither of these decorations is required for normal O-antigen length, transport, or assembly into the final lipopolysaccharide. This is in contrast to certain enteric bacteria in which the absence of a terminal decoration severely affects O-antigen length and transport.R. etlimutants lacking only the methylated terminal fucose were not altered in symbiosis with hostPhaseolus vulgaris, whereas mutants lacking only 2-O-methylfucose exhibited a delay in nodule development during symbiosis. These results support previous conclusions that the methylated terminal fucose is dispensable for symbiosis, whereas 2-O methylation of internal fucoses somehow facilitates early events in symbiosis.