کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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6456506 | 1420185 | 2016 | 10 صفحه PDF | دانلود رایگان |
- Bicistronic coexpression platform for conversion of substrates which translocate poorly through the outer E. coli membrane.
- Quantification of outer membrane pore, FhuA Î1-160 Strep, through a fluorescent label enables to compare specific translocation efficiencies.
- Translocation efficiencies of aromatics andterpenes increased by a factor of up to five.
- Final concentration of oxidized aromatics and terpenes was doubled in E. coli expressing FhuA Î1-160 along with cytochrome P450.
- Bicistronic coexpression platform can likely be extended to other enzyme classes and substrates.
Biocatalysis with cytochrome P450 enzymes are important for the industrial production of fine chemicals, pharmaceuticals, fragrance and flavor compounds since chemoselective hydroxylation of aromatics and terpenes are chemically difficult to achieve. A few P450 based industrial processes have been developed based on whole cell catalysis. However, the outer membrane of microbial cells forms an effective barrier, which reduces the uptake of hydrophobic substrates. The coexpression of outer membrane proteins in E. coli such as the ferric hydroxamate uptake protein (FhuA) can provide alternative solutions to chemical or physical methods for increasing compound flux through the outer membrane of E. coli and thereby to boost productivities. In this study we employed an engineered FhuA Î1-160 variant in which the “cork domain” was removed (first 160 residues are deleted); FhuA Î1-160 has a cross-section of 39-46 à with a “free” inner diameter of about 14 à that serves as passive diffusion channel. FhuA WT and Î1-160 were coexpressed on a bicistronic system with two P450 BM3 variants for regiospecific hydroxylation of aromatic compounds toluene and anisole as well as for oxidation of two terpenes (α)-pinene and (R)-(+)-limonene. The presence of FhuA Î1â160 resulted in a doubled product concentration for toluene (35 μ to 50 μM), anisole (25 μM to 45 μM), pinene (12 μM to 20 μM) and limonene (12 μM to 25 μM) and five times higher for the coumarin derivative BCCE. In order to characterizes and compensate for expression variations a quantification method based on Chromeo546-labled StrepTactinII was developed to quantify the number of FhuA Î1-160 in the outer E. coli membrane (â¼44000 of FhuA Î1-160 per cell). Morphology studies showed that a 6% E. coli surface coverage can be achieved with FhuA Î1â160 without significantly influencing the E. coli rod shape. In summary, FhuA Î1-160 efficiently increases uptake of hydrophobic aromatics and terpenes for whole-cell biotransformations and can likely be used for other enzymes and/or substrates.
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Journal: Journal of Molecular Catalysis B: Enzymatic - Volume 134, Part B, December 2016, Pages 285-294