理性设计和构建过量合成莽草酸的大肠杆菌代谢工程菌

Rational design and construction of an overproducing shikimic acid Escherichia coli by metabolic engineering

摘要:

利用代谢工程手段理性改造野生大肠杆菌的莽草酸 (SA) 合成途径及相关代谢节点，以构建高产莽草酸的工程菌株。根据细胞代谢网络分析，利用Red-Xer重组系统连续删除了野生型大肠杆菌CICIM B0013的莽草酸激酶基因 (aroL、aroK)，葡萄糖磷酸转移酶系统 (PTS) 的关键组分EIICBglc的编码基因 (ptsG) 以及奎宁酸/莽草酸脱氢酶基因 (ydiB) 并系统评价了基因删除对细胞的生长、葡萄糖代谢和莽草酸积累的影响。aroL、aroK的删除阻断了莽草酸进一步转化成为莽草酸-3-磷酸，初步提高莽草酸的累积。删除ptsG基因使大肠杆菌PTS系统部分缺失，细胞通过GalP-glk (半乳糖透性酶-葡萄糖激酶) 途径，利用ATP将葡萄糖磷酸化后进入细胞。利用该途径运输葡萄糖能够减少PEP的消耗，使得更多的碳代谢流进入莽草酸合成途径，从而显著提高了莽草酸的产量。在此基础上删除ydiB基因，阻止了莽草酸合成的前体物质3-脱氢奎宁酸转化为副产物奎宁酸 (Quinic acid，QA)，进一步提高了莽草酸的累积。初步发酵显示4个基因缺失的大肠杆菌代谢工程菌生产莽草酸的能力比原始菌提高了90多倍。

Abstract:

Shikimic acid (SA), as a hydroaromatic intermediate in the common pathway of aromatic amino acid biosynthesis, is the starting material for the synthesis of neuraminidase inhibitors and other useful compounds. The fermentative production of SA by metabolically engineered microorganisms is an excellent alternative to the extraction from fruits of the Illicium plant. In this study, Escherichia coli was metabolically engineered by rational design and genetic manipulation for fermentative production of SA. First, blocking the aromatic amino acid pathway after the production of SA was carried out by deletion of aroL and aroK genes encoding SA kinase. Second, the ptsG gene encoding protein EIICBglc were removed in the aroL/aroK mutant strain to make the phosphotransferase system (PTS) system default. In the resulting strain, the phosphoenolpyruvate-dependent PTS pathway, a main pathway for glucose transport, were replaced by ATP-dependent GalP (galactose permease). Thus, more PEP flux was used to produce SA as a critical precursor of SA. Furthermore, ydiB gene (encoding quinic acid/SA dehydrogenase) was deleted to prevent SA precursors of 3-dehyroquinic acid into the byproduct of quinic acid. Thus, the engineered strain with four genes deletion was constructed and 576 mg/L SA was produced in the shake flask fermentation. Results show that SA produciton was increased 90 times compared to the parent strain E. coli CICIM B0013.