The essential tacF gene is responsible for the choline-dependent growth phenotype of Streptococcus pneumoniae
The essential tacF gene is responsible for the choline-dependent growth phenotype of Streptococcus pneumoniae
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DOI：
10.1128/jb.00681-07
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发表时间：
2007-10-01
影响因子：
3.2
通讯作者：
Vollmer, Waldemar
中科院分区：
文献类型：
--
作者：
Damjanovic, Marlen;Kharat, Arun S.;Vollmer, Waldemar
肺炎链球菌对胆碱具有绝对的营养需求，并且已知胆碱分子仅掺入细菌的细胞壁和膜磷壁酸中。我们在这里描述了分离菌株R6的突变体，其中基因tacF（以前命名为spr 1150）中的单个G -> T点突变负责产生胆碱非依赖性表型。通过用PCR产物或用携带突变tacF基因的质粒进行遗传转化，可以将胆碱非依赖性表型转移到实验室菌株R6和包囊菌株D39中。tacF基因产物属于多糖跨膜转运蛋白（翻转酶）的蛋白质家族。提出了一个模型，其中TacF是需要跨细胞质膜的磷壁酸亚基的运输。根据该模型，野生型TacF对含胆碱的亚基具有严格的特异性，而存在于胆碱非依赖性突变株中的TacF能够运输含胆碱和无胆碱的磷壁酸链。建议的运输特异性的亲本型TacF含胆碱的亚基将确保加载的细胞壁与磷壁酸链装饰胆碱残基，这似乎是必不可少的这种病原体的毒力。
Streptococcus pneumoniae has an absolute nutritional requirement for choline, and the choline molecules are known to incorporate exclusively into the cell wall and membrane teichoic acids of the bacterium. We describe here the isolation of a mutant of strain R6 in which a single G -> T point mutation in the gene tacF (formerly designated spr1150) is responsible for generating a choline-independent phenotype. The choline-independent phenotype could be transferred to the laboratory strain R6 and to the encapsulated strain D39 by genetic transformation with a PCR product or with a plasmid carrying the mutated tacF gene. The tacF gene product belongs to the protein family of polysaccharide transmembrane transporters (flippases). A model is presented in which TacF is required for the transport of the teichoic acid subunits across the cytoplasmic membrane. According to this model, wild-type TacF has a strict specificity for choline-containing subunits, whereas the TacF present in the choline-independent mutant strain is able to transport both choline-containing and choline-free teichoic acid chains. The proposed transport specificity of parental-type TacF for choline-containing subunits would ensure the loading of the cell wall with teichoic acid chains decorated with choline residues, which appear to be essential for the virulence of this pathogen.