The Riboswitch Regulates a Thiamine Pyrophosphate ABC Transporter of the Oral Spirochete Treponema denticola
The Riboswitch Regulates a Thiamine Pyrophosphate ABC Transporter of the Oral Spirochete Treponema denticola
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DOI：
10.1128/jb.00386-11
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发表时间：
2011-08-01
影响因子：
3.2
通讯作者：
Li, Chunhao
中科院分区：
文献类型：
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作者：
Bian, Jiang;Shen, Hongwu;Li, Chunhao
焦磷酸硫胺素 (TPP) 是硫胺素（维生素 B-1）的一种生物活性形式，是所有生命系统中必需的辅助因子。微生物要么通过从头生物合成途径合成TPP，要么通过特定转运蛋白从环境中摄取外源硫胺素。口腔螺旋体齿垢密螺旋体是与人类牙周病相关的重要病原体。它缺乏从头TPP生物合成途径，需要外源TPP才能生长，这表明它可能通过硫胺素转运蛋白获得外源TPP。在这项研究中，我们鉴定了一个编码 TPP ABC 转运蛋白的基因簇，该转运蛋白由 TPP 结合蛋白 (TDE0143)、跨膜通透酶 (TDE0144) 和胞质 ATP 酶 (TDE0145) 组成。转录和翻译分析表明，编码这三种蛋白质的基因被共转录并形成由 sigma(70) 样启动子启动的操纵子 (tbpABC(Td))。该操纵子的表达水平受外源 TPP 负调节，并由 TPP 感应核糖开关 (Td(thi-box)) 介导。遗传和生化研究表明，TDE0143缺失突变体（T. denticola Delta tbpA）转运外源TPP的能力下降，当外源TPP不足时，突变体无法生长。这些结果综合表明，tbpABC(Td)操纵子编码吸收外源TPP所需的ABC转运蛋白，并且该操纵子的表达由TPP结合核糖开关通过反馈抑制机制调节。
Thiamine pyrophosphate (TPP), a biologically active form of thiamine (vitamin B-1), is an essential cofactor in all living systems. Microorganisms either synthesize TPP via de novo biosynthesis pathways or uptake exogenous thiamine from the environment via specific transporters. The oral spirochete Treponema denticola is an important pathogen that is associated with human periodontal diseases. It lacks a de novo TPP biosynthesis pathway and needs exogenous TPP for growth, suggesting that it may obtain exogenous TPP via a thiamine transporter. In this study, we identified a gene cluster that encodes a TPP ABC transporter which consists of a TPP-binding protein (TDE0143), a transmembrane permease (TDE0144), and a cytosolic ATPase (TDE0145). Transcriptional and translational analyses showed that the genes encoding these three proteins are cotranscribed and form an operon (tbpABC(Td)) that is initiated by a sigma(70)-like promoter. The expression level of this operon is negatively regulated by exogenous TPP and is mediated by a TPP-sensing riboswitch (Td(thi-box)). Genetic and biochemical studies revealed that the TDE0143 deletion mutant (T. denticola Delta tbpA) had a decreased ability to transport exogenous TPP, and the mutant failed to grow when exogenous TPP was insufficient. These results taken together indicate that the tbpABC(Td) operon encodes an ABC transporter that is required for the uptake of exogenous TPP and that the expression of this operon is regulated by a TPP-binding riboswitch via a feedback inhibition mechanism.