Regulation of gbpC expression in Streptococcus mutans
Regulation of gbpC expression in Streptococcus mutans
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DOI：
10.1128/jb.00825-07
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发表时间：
2007-09-01
影响因子：
3.2
通讯作者：
Biswas, Saswati
中科院分区：
文献类型：
--
作者：
Biswas, Indranil;Drake, Laura;Biswas, Saswati
变形链球菌（Streptococcus mutans）是龋病的主要致病菌，其产生的四种葡聚糖结合蛋白（Gbp）在细菌粘附和致病中起主要作用。这些蛋白质之一，GbpC，是参与生物膜形成的重要细胞表面蛋白。GbpC对龋齿发生、菌血症和感染性心内膜炎也很重要。在这项研究中，我们研究了gbpC在S.变异株UA 159。我们发现，gbpC的表达达到最高水平，在指数生长中期，和转录的半衰期小于2分钟。从PgbpC的表达进行了测量，使用PgbpC-gusA转录融合报告，并在各种应力条件下进行了分析，包括热，渗透，和酸应力。gbpC的表达诱导条件下的热应力，但在低pH值的生长过程中被抑制，而渗透压应力对PgbpC的表达没有影响。使用半定量逆转录-PCR分析进一步证实了表达分析的结果。我们的研究结果还揭示了CovR，一种在许多链球菌属中的全局反应调节因子，在转录水平抑制gbpC表达。我们证明，纯化的CovR蛋白直接结合到PgbpC的启动子区，以抑制gbpC的表达。使用DNase I保护试验，我们表明CovR与PgbpC周围碱基-68至28（其中碱基1是转录的起点）的DNA序列结合。总之，我们的研究结果表明，各种压力条件下调节gbpC的表达和CovR负调控gbpC基因的表达，直接结合到启动子区。
Streptococcus mutans, the principal causative agent of dental caries, produces four glucan-binding proteins (Gbp) that play major roles in bacterial adherence and pathogenesis. One of these proteins, GbpC, is an important cell surface protein involved in biofilm formation. GbpC is also important for cariogenesis, bacteremia, and infective endocarditis. In this study, we examined the regulation of gbpC expression in S. mutans strain UA159. We found that gbpC expression attains the maximum level at mid-exponential growth phase, and the half-life of the transcript is less than 2 min. Expression from PgbpC was measured using a PgbpC-gusA transcriptional fusion reporter and was analyzed under various stress conditions, including thermal, osmotic, and acid stresses. Expression of gbpC is induced under conditions of thermal stress but is repressed during growth at low pH, whereas osmotic stress had no effect on expression from PgbpC. The results from the expression analyses were further confirmed using semiquantitative reverse transcription-PCR analysis. Our results also reveal that CovR, a global response regulator in many Streptococcus spp., represses gbpC expression at the transcriptional level. We demonstrated that purified CovR protein binds directly to the promoter region of PgbpC to repress gbpC expression. Using a DNase I protection assay, we showed that CovR binds to DNA sequences surrounding PgbpC from bases -68 to 28 (where base 1 is the start of transcription). In summary, our results indicate that various stress conditions modulate the expression of gbpC and that CovR negatively regulates the expression of the gbpC gene by directly binding to the promoter region.