DnaB Split Intein高表达载体及其介导的环肽库构建

Construction and Evaluation of DnaB Split Intein High Expression Vector and a Six Amino Acids Cyclic Peptide Library

以pET28a为起始质粒,构建高表达DnaB split intein的重组质粒。将质粒pVmut上的编码IntC-dnaB-N-IntN片段克隆至pET28a,得到表达载体pEV,在T7启动子的作用下可使融合DnaB split intein大量表达;并在split intein介导下发生催化DnaB-N的剪接反应,生成环化的DnaB-N蛋白。将合成的包含随机编码5肽的大小为115 bp的片段插入质粒pEV DnaB-N位置,转化大肠杆菌后得到一个编码含有6肽(含5个随机氨基酸和1个Cys)的包含约103个克隆的表达载体pEV-IS库。随机挑取20个克隆,测序证明均按正确阅读框插入了不同的小肽序列;挑取其中9个克隆进行表达,结果表明可产生大量的融合蛋白,90%的融合蛋白在16oC表达20 h后发生体内剪接。将在30oC表达3 h的融合蛋白用His柱进行纯化,通过MALDI-TOF质谱检测到了目的环肽分子量。

A library with potential to produce six amino acids cyclic peptides was prepared using pET-28a as the starting plasmid. pVmut was used to amplify the Intc-dnaB-N-IntN fragment that was inserted into pET28a to give pEV. On pEV, DnaB split intein was expressed under the strong T7 promoter. Analyses of Escherichia coli transformed with pEV showed that DnaB split intein was produced in large quantity and the fusion protein self-spliced efficiently to produce cyclized DnaB-N. A synthesized 115 bp fragment mixture encoding 5 random amino acids was inserted into pEV to generate pEV-IS. The ligation mixture was transformed into E. coli A library of 10^3 clones was obtained, 20 randomly picked clones were sequenced. All of them contain different sequences. Nine clones were chosen for further analysis. Split-intein-ISs were expressed in large quantity, and 90% of them self-spliced under 16℃ in 20 hours. After induction at 30℃ for 3 hours, the expressed DnaB split intein was purified using His-column, and then a molecular weight of target cyclic peptide was detected by MALDI-TOF-MS.