Part:BBa_K1088004
IspG (1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate synthase)
1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate synthase (IspG) is part of the bacterial MEP (methylerythritol phosphate) pathway used for production of isoprenoids.
From ecocyc: "IspG catalyzes the conversion of 2C-methyl-D-erythritol 2,4-cyclodiphosphate into 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate. IspG activity depends on as-yet unidentified additional proteins, most likely involved in the oxidation portion of the reaction" [http://www.ecocyc.org/ECOLI/NEW-IMAGE?type=GENE&object=EG10370 (Link)]
Usage and Biology
Characterized by SEFLS_SHANGHAI
Construction of the plasmids pET-IAY, pET-IAY-CN, pET-HIAY and pMEP-DG
1. Obtain the target fragments YSS, DXS, ispH, ispG and IIA(rbs-idi-rbs-ispA)
Gene dxs, ispH and ispG were obtained by PCR from E. coli, and IIA fragment was obtained by PCR using plasmid p35151 as template. The following figure shows the fragment YSS, ispH, DXS, ispG and IIA after gel recycling.
2. Conduct double enzyme digestion on the skeleton vectors pBBR1MCS-2, pETDuet-1 and pET-YN, respectively. pBBR1MCS-2 is the skeleton of pMEP-DG, pETDuet-1 is the skeleton of pET-IAY and pET-HIAY, and pET-YN is the skeleton of pET-IAY-CN.
3. The plasmid skeleton recovered by enzyme digestion and the target fragment recovered by gel were verified by electrophoresis. The results are shown below:
4. Connect the homologous recombinant fragment with the corresponding backbone, the ligation reaction system is as follows:
pET-IAYďź The enzyme digestion product of pET Duet-1 +IIA+YSS
pET-HIAYďź The enzyme digestion product of pET Duet-1 +ispH+IIA+YSS
pET-IAY-CNďź The enzyme digestion product of pET-YN + IIA+YSS
pMEP-DGďź The enzyme digestion product of pBBR1MCS-2 +dxs+ispG
During transformation, we encountered some difficulties, for example, there were many clones on the plate, but none of them is the positive transformant. Later, we solved this problem by adding DpnI enzyme to the PCR product and speculated that the concentration of plasmid template added was too high when preparing the PCR reaction solution, resulting in excessive negative transformant growing on the plate. We encountered situation where there was no clone on the plate. After increasing the concentration of products from plasmid enzyme digestion and decreasing the concentration of products from gel recycling, this problem is resolved. We speculated that the problem may be due to the low concentration of products from plasmid enzyme digestion and the high concentration of fragment from gel recycling, which affected the accuracy of the ligation reaction system. The addition of plasmids and ligated fragments that are not in the proper range may lead to the failure of ligation reactions.
5. Monoclones on the transformation plate were selected for bacterial solution PCR verification, and the verification results were as follows, indicating that plasmids pET-IAY, pET-IAY-CN, pET-HIAY and pMEP-DG were successfully constructed.
The genes dxs and ispG were placed on the backbone of low-copy plasmid pBBR1MCS-2, and the promoter was medium strength lac promoters, to construct plasmid pBBR1MCS-2-dxs-ispG (pMEP-DG).
Genes ispH, idi, and ispA were placed on the backbone of high-copy plasmid pETDuet-1, and the promoter was strong promoter T7 to construct plasmid pETDuet-1-1T7-IspH-Idi-IspA-Yss (pET-HIAY).
When Dxs and IspG were overexpressed, the squalene yield increased by 4.3 times. We speculated that the overexpressed gene ispG was constructed on low-copy plasmids and was controlled by promoters of medium strength, so it didnât produce large amounts of harmful intermediate HMBPP. And overexpressing Dxs promoted the metabolic flow, increasing the squalene yield.
H3: p35151/pET-HIAY
H5: p35151/pMEP-DG/pET-HIAY
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