【摘要】 【目的】转酮酶是非氧化磷酸戊糖途径中的关键酶。从北京棒杆菌(Corynebacterium pekinense PD-67)中克隆转酮酶(transketolase,EC2.2.1.1,TK)基因,并将转酮酶基因在C.pekinense PD-67中进行表达,研究增加转酮酶活性对C.pekinense PD-67生理特性的影响。【方法】分别以C.pekinense野生株AS1.299和突变株PD-67的基因组为模板,用PCR方法扩增tkt的全基因序列和前端控制序列;通过pAK6载体提高tkt基因在C.pekinense PD-67中的拷贝数,从而提高C.pekinense PD-67中转酮酶的活性。【结果】tkt基因核苷酸序列及其编码的氨基酸序列与结构分析结果表明,C.pekinense突变株PD-67与野生株AS1.299相比较,二者调控序列及结构基因核苷酸序列完全一致。与谷氨酸棒杆菌ATCC13032相比较,突变株PD-67的氨基酸序列有5个氨基酸差异,其中4个位于与辅因子硫胺素焦磷酸结合的结构域内。突变株PD-67来源的tkt基因在北京棒杆菌PD-67中得到了表达,重组菌转酮酶比活力比对照菌株提高了2倍。C.pekinense PD-67(pTK3)与对照菌株PD-67(pAK6)相比,生长加快,L-色氨酸的最终积累量也较高。【结论】本工作从C.pekinense1.299和PD-67中克隆到tkt基因,并实现tkt基因的同源表达。适当提高菌株转酮酶活力,有助于菌体生长和色氨酸积累。更多还原

【Abstract】 [Objective]Transketolase (EC 2. 2. 1. 1;TK) is the key enzyme in non-oxidative phosphate pentose pathway. We cloned tkt gene from Corynebacterium pekinense AS 1. 299 and its mutant PD-67 in order to investigate the effect of gene expression on physiological characteristics of C. pekinense. PD-67. [Methods]According to the homology between Corynebacterium glutamicum ATCC13032 and C. pekinense,we designed a pair of PCR primers to clone the tkt gene from wild-type C. pekinense AS1. 299 and its mutant PD-67,then the mutant tkt gene was expressed in C. pekinense PD-67 by subcloning the PCR fragment into plasmid pAK6. The physiological characteristics of the recombinant C. pekinense PD-67 was investigated by fermentation. [Results]Analysis of PCR fragments reveals that,besides the regulatory sequence,they contain the whole structure of tkt gene. There is no base change all over the structure genes and regulatory sequences between C. pekinense AS1. 299 and PD-67. Comparing with Corynebacterium glutamicum ATCC 13032,there exist 5 amino acids change in amino acid sequence. Four of them were located in the motifs involved in thiamine pyrophosphate binding sites. The tkt gene from C. pekinense PD-67 was expressed homogenously,and the specific enzyme activity of TK in C. pekinense PD-67(pTK3) is two times over that of the control strain C. pekinense PD-67(pAK6). The recombinant C. pekinense PD-67 exhibits higher cell mass and accumulation of more tryptophan. [Conclusion ] The moderate amplification of TK activity resulted in increase of L-tryptophan production without affecting the cell growth.更多还原