茶碱激活型RNA分子开关的构建及在枯草芽胞杆菌中调节外源基因表达的性能

Construction and application of theophylline-activated RNA switches in the regulation of expression of recombinant proteins in Bacillus subtilis

摘要:

枯草芽胞杆菌Bacillus subtilis在工业生物技术以及合成生物学领域作为一种重要的微生物可广泛用作代谢工程、重组蛋白表达以及新型基因电路的底盘。在B. subtilis中构建基于非编码RNA的高精准调节元件，能够实现不依赖蛋白质因子的基因表达调控，丰富B. subtilis基因表达通用工具。通过基因工程手段，设计了基于茶碱适体域的核糖开关E和适体核酶AZ调节元件，并与不同的B. subtilis内源组成型启动子适配，构建出茶碱激活型基因表达控制元件。测定这两种调节元件与6种组成型启动子组合匹配下报告基因GFP的荧光强度，鉴定并分析各调控元件的工作性能。并进一步以红色荧光蛋白mCherry和普鲁兰酶两种不同的异源蛋白验证核糖开关或适体核酶与启动子的最优组合。结果表明，同一种RNA调节元件与不同启动子组合呈现不同水平的调控效率。在核糖开关与启动子的组合中，启动子PsigW和核糖开关E组合 (sigWE) 对GFP表达的诱导率最高，达到16.8。在适体核酶与启动子的组合中，AZ与启动子P43、PrpoB组合 (P43AZ和rpoBAZ) 的诱导率最高，分别达到了6.1和6.2。进一步验证结果显示，sigWE调控mCherry的诱导率最高 (9.2)，而P43E调控普鲁兰酶的诱导率最高 (32.8)，产酶水平达到了81 U/mL。核糖开关和适体核酶对GFP、mCherry、普鲁兰酶均能实现调控，但是不同元件组合的调控性能有所差异，对不同基因的调控效果也不尽相同。

Abstract:

Bacillus subtilis can be widely used as an important microorganism for metabolic engineering and recombinant proteins expression in industrial biotechnology and synthetic biology. However, it is difficult to make accurate regulation of exogenous gene by biological tools in B. subtilis, which limits the application of B. subtilis in synthetic biology. The purpose of this study is to develop regulatory tools for precise control of gene expression by using non-coding RNAs, by which the activation of heterologous gene could be achieved without the auxiliary protein factors. We constructed the synthetic riboswitch E and aptazyme AZ using the theophylline aptamer. Six different native promoters from B. subtilis were functionally adapted with the E and AZ to fabricate an array of novel regulatory elements activated by theophylline. Then, we determined the performance of these elements using green fluorescence protein as reporter, and then further verified using red fluorescence protein and pullulanase as cargo proteins. Results showed that the same kind of RNA elements with different promoters showed different levels of efficiency. Promoter PsigW and E combination (sigWE) had the highest induction rate in B. subtilis. Compared with the control group, it can produce the induction rate of 16.8. Promoter PrpoB and AZ combination (rpoBAZ) showed the highest induction rate of 6.2. SigWE mediated mCherry induction rate was 9.2, and P43E mediated pullulanase induction rate was 32.8, in which enzyme activity reached 81 U/mL. This study confirmed that GFP, mCherry and pullulan can all be regulated by riboswitch and aptazyme, but there were differences between different combinations of promoters with RNA regulators.