sepM突变在变异链球菌变链素IV形成中的作用及其分子调控机制

龋病是危害居民口腔健康最常见的疾病之一。变异链球菌（SM）是导致龋病发生的重要病原菌，而格氏链球菌（SG）是抑制SM生长的非致龋菌。变链素IV是SM产生的拮抗SG生长、推动龋病发生的重要细菌素。研究报道，SepM是SM表达的正调控变链素IV形成的关键蛋白质。我们预实验发现，该蛋白编码基因sepM的G533A和G661A突变与变链素IV的形成呈正相关，并且G533A临床突变株的致龋性显著高于对照组。因此，本项目计划围绕“SM的sepM基因G533A和G661A突变是否在变链素IV的形成中起重要促进作用”这一科学问题，探索这些突变调控变链素IV形成的能力，并分析突变对sepM基因转录、SepM蛋白表达和剪切活性、下游ComDE双组份调控系统磷酸化水平、变链素IV编码基因nlmA和nlmB的转录水平及启动子活性的影响，进一步揭示口腔定植菌交互作用调控龋病发生的机制，为临床龋病防治提供理论依据。

Dental caries is one of the most common diseases that damage the oral health of residents. Streptococcus mutans (SM) is recognized as an important pathogen causing dental caries, while Streptococcus gordonii (SG) is a non-cariogenic bacterium which can inhibit the growth of SM. Mutacin IV is an important bacteriocin produced by SM to antagonize SG growth and promote dental caries. It has been reported that SepM is a key protein produced by SM that positively regulates the formation of mutacin IV. Our preliminary studies showed that G533A and G661A mutations of sepM gene coding for SepM protein were positively correlated with the production of mutacin IV, and the cariogenic capacity of the clinical isolate with G533A mutation was significantly higher than that of the control group. Therefore, this study aims to focus on the scientific issue of "whether G533A and G661A mutations of sepM gene play an important role in promoting the formation of mutacin IV in SM", verify the role of these mutations in the formation of mutansin IV, analyze the effects of mutations on the transcription of sepM gene, the expression level and shear activity of SepM protein, the phosphorylation level of downstream ComDE two-component regulatory system, and the expression levels and the promoter activity of the code genes (nlmA and nlmB) of mutacin IV. This project further reveals the mechanism of the interaction of oral colonization bacteria in the regulation of the onset of dental caries, and provides a theoretical basis for the prevention and treatment of clinical caries.