Osmotic Control of opuA Expression in Bacillus subtilis and Its Modulation in Response to Intracellular Glycine Betaine and Proline Pools
Osmotic Control of opuA Expression in Bacillus subtilis and Its Modulation in Response to Intracellular Glycine Betaine and Proline Pools
复制标题
DOI：
10.1128/jb.01505-12
复制
发表时间：
2013-02-01
影响因子：
3.2
通讯作者：
Bremer, Erhard
中科院分区：
文献类型：
--
作者：
Hoffmann, Tamara;Wensing, Annette;Bremer, Erhard
甘氨酸甜菜碱是一种有效的枯草芽孢杆菌芽孢保护剂。它的进口到渗透胁迫的细胞导致大池的积累，其大小是由所施加的渗透胁迫的程度敏感地确定。甘氨酸甜菜碱的积累抑制了脯氨酸的胁迫适应性库的形成，而脯氨酸是B的唯一的植物保护剂。subtilis可以从头合成。ABC转运蛋白OpuA是B的主要甜菜碱摄取系统。枯草芽孢杆菌opuA的表达上调响应突然和持续增加的外部渗透压。非离子型渗透剂比离子型渗透剂对转录产生更强的诱导作用，这反映在相应OpuA介导的甘氨酸甜菜碱池的发展中。引物延伸分析和定点突变确定了渗透压控制的opuA启动子。SigA型启动子的共有序列的偏差用于在不存在渗透胁迫的情况下保持opuA启动子的低转录活性。opuA的表达被下调，在一个微调的方式在细胞内甘氨酸甜菜碱池的增加，无论这种甜菜碱保护剂是进口或新合成的胆碱。这种作用也是由肉毒碱，一种有效的维生素保护剂B。枯草芽孢杆菌，其不是OpuA转运蛋白的底物。opuA表达在a B中上调。枯草杆菌突变体不能合成脯氨酸响应渗透胁迫。总的来说，我们的数据表明，细胞内溶质池是opuA表达的渗透控制的关键决定因素。
Glycine betaine is an effective osmoprotectant for Bacillus subtilis. Its import into osmotically stressed cells led to the buildup of large pools, whose size was sensitively determined by the degree of the osmotic stress imposed. The amassing of glycine betaine caused repression of the formation of an osmostress-adaptive pool of proline, the only osmoprotectant that B. subtilis can synthesize de novo. The ABC transporter OpuA is the main glycine betaine uptake system of B. subtilis. Expression of opuA was upregulated in response to both sudden and sustained increases in the external osmolarity. Nonionic osmolytes exerted a stronger inducing effect on transcription than ionic osmolytes, and this was reflected in the development of corresponding OpuA-mediated glycine betaine pools. Primer extension analysis and site-directed mutagenesis pinpointed the osmotically controlled opuA promoter. Deviations from the consensus sequence of SigA-type promoters serve to keep the transcriptional activity of the opuA promoter low in the absence of osmotic stress. opuA expression was downregulated in a finely tuned manner in response to increases in the intracellular glycine betaine pool, regardless of whether this osmoprotectant was imported or was newly synthesized from choline. Such an effect was also exerted by carnitine, an effective osmoprotectant for B. subtilis that is not a substrate for the OpuA transporter. opuA expression was upregulated in a B. subtilis mutant that was unable to synthesize proline in response to osmotic stress. Collectively, our data suggest that the intracellular solute pool is a key determinant for the osmotic control of opuA expression.