转录因子FabT介导的肺炎链球菌荚膜多糖合成调控的分子机制

Capsule is the key virulence factor of streptococcus pneumoniae(S.pn).It was discovered by Griffith F in 1928 that the amount of capsule in S.pn was regulated by environmental signal. However, the molecular mechanism of this phenomenon was barely understood. Our previous results showed that the synthesis of capsular polysaccharide was negatively regulated by transcription factor FabT and affected by two-component system(TCS) YycFG which could feel the environmental signal stimulation. As it has been proved that YycF could play a negative regulation role in FabT expression, we hypothesize that while stimulated by environmental signal, YycFG could affect the synthesis of pneumococcal capsular polysaccharide by regulating the expression of FabT. To comfirm the synthesis, a mutant streptococcus pneumoniae strain of related genes and gene promoter sequences is intended to be constructed in this study and be cultured in different internal and external environment together with wild-type strain. The regulation of YycFG-FabT pathway on the synthesis of capsular polysaccharide and related environmental signals would be confirmed by comparing the amount of capsular polysaccharide ,expression of related genes and phospholaration of YycFG in these two strains. This study would provide experimental evidences for the further understanding of molecular mechanisms on bacteria’s adaptation to the different internal environment and consequent change of virulence, also for answering the scientific question of how S.pn regulate the expression of capsule.

荚膜是肺炎链球菌（S.pn）的一种关键毒力因子，1928年Griffith F就发现S.pn的荚膜含量受环境信号的调控，但这个“古老”现象的分子机制至今未能阐明。本课题组前期发现转录因子FabT可负调控S.pn荚膜多糖的合成，能感受环境信号刺激的双组份系统YycFG可影响S.pn荚膜多糖的合成。文献已证实YycF可负调控FabT的表达。因此推测，YycFG受环境信号刺激后，可调控FabT的表达而影响S.pn荚膜多糖的合成。为验证该假说，本研究拟构建启动子序列及其相关基因的S.pn突变菌株，在不同体内、外环境培养这些突变菌与野生菌，比较其荚膜多糖含量、相关基因表达及YycFG的磷酸化水平，以确定YycFG-FabT通路对S.pn荚膜多糖合成的调控以及参与调控的环境信号。本研究为理解细菌适应体内不同环境、导致毒力改变的机制、并为回答S.pn调控荚膜多糖合成这个“古老”的科学问题提供实验证据。

荚膜是肺炎链球菌（S.pn）的一种关键毒力因子，其含量受环境信号的调控，如在血液中荚膜增厚以更好的逃避免疫细胞的吞噬，而在鼻咽呼吸道粘液中往往荚膜减少以增加粘附，但其分子机制至今未能阐明。本课题组前期发现转录因子FabT可影响S.pn荚膜多糖的合成，而该因子被报道能被双组份系统YycFG调控，后者可以感受环境信号的变化。因此本研究拟探索YycFG是否通过FabT调节S.pn荚膜多糖的合成，参与感受环境信号对荚膜的调控。本研究结果表明FabT可通过调节细菌相变的方式正调控肺炎链球菌的CPS含量，进而调控细菌的毒力。确证了YycFG可负调控细菌CPS含量，调控细菌的毒力，但不是通过FabT通路实现的，也不是通过cps基因座的转录调控实现的。体内模拟环境（血清培养）可使肺炎链球菌的荚膜增加，但不依赖于cps基因座的调控，也与FabT和YycFG不相关，很可能与碳水化合物代谢途径的调控相关。本研究结果为回答S.pn荚膜多糖合成调控这个“古老”的科学问题提供了新的实验证据，并为理解细菌适应体内不同环境、导致毒力改变的机制提供了新的线索。