金荞麦苯丙氨酸解氨酶基因FdPAL 的克隆及原核表达

目的:克隆金荞麦苯丙氨酸解氨酶(FdPAL)基因DNA和全长cDNA序列,对该基因进行序列分析,原核表达及其活性相关研究.方法:采用同源克隆和RT-PCR技术扩增苯丙氨酸解氨酶基因的DNA序列和全长cDNA序列并对其进行生物信息学分析；构建PAL原核表达载体pET30b(+)-FdPAL,在大肠杆菌Escherich coli BL21( DE3)中进行诱导表达,使用分光光度计法定量测定其酶活,使用薄层色谱法鉴定其催化活性.结果:金养麦PAL基因DNA序列全长2 583 bp,由2个外显子,1个内含子构成(命名为FdPAL,GenBank登录号为HM628904)；cDNA序列包含1个2 169 bp的开放阅读框(ORF),编码722个氨基酸,理论相对标准分子质量78.31 kDa,等电点5.94.SDS-PAGE分析表明,诱导后的新生蛋白质相对标准分子质量为75.37 kDa;诱导4h后,表达产物的苯丙氨酸解氨酶比活力最高,达到4 386 nmol·g-1·min-；薄层色谱结果表明,诱导表达产物具有催化苯丙氨酸转化为肉桂酸的活性.结论:首次从金荞麦中克隆到PAL基因,该基因具有植物PAL同源基因的典型特征；重组的金荞麦PAL基因表达载体[pET30b(+)-FdPAL]能有效地在大肠杆菌Ecoli BL21 (DE3)中表达,并形成具有一定催化功能的酶.

Molecular cloning and prokaryotic expression of phenylalanine ammonia- lyase gene FdPAL from Fagopyrum dibotrys

Objective: To clone and characterize the DNA and cDNA sequences of phenylalanine ammonia-lyase gene (PAL) from Fagopyrum dibotrys, and investigate the biological activity of the obtained PAL. Method: Using homology cloning and RT-PCR techniques, the DNA and full-length cDNA sequences of PAL gene were amplified from F. dibotrys. The obtained sequences were analyzed by bioinformatics software. The ORF of PAL gene was cloned into expression vector pET-30b(+) and transformed into Escherichia coli BL21(DE3) for expression the recombined protein. The catalytic activity of the recombined protein was determined by spectrophotometer and thin layer chromatography (TLC) methods. Result: The DNA sequence of PAL gene (designated as FdPAL, GenBank accession number: HM628904) was 2 583 bp in size, of which consisted two extrons and a single intron, and the full-length cDNA of FdPAL was 2 169 bp in size, which contained an ORF. The deduced protein of FdPAL contained 722 amino acids with calculated molecular weight (MW) of 78.31 kDa and an isoelectric point (pI) of 5.94. The SDS-PAGE results showed that the molecular weight of recombinant FdPAL protein was 75.37 kDa,which is consistent with the predictions. After 4 hours of induction, the enzymatic specific activity of FdPAL reached the summit, up to 4 386 nmol·g^-1·min^-1. The reaction products were also identified by TLC, using L-Phe and trans-cinnamic acid as the internal standard. Conclusion: The PAL gene (both DNA sequence and full-length cDNA sequence) was cloned from F. dibotrys, and it has the same classic characters as other PALs in plants. The recombinant FdPAL was efficiently expressed in E. coli and had the activity for catalyzing the conversion from L-phenylalanine to cinnamic acid.