Biosynthetic Pathway for the Cyanide-Free Production of Phenylacetonitrile in Escherichia coli by Utilizing Plant Cytochrome P450 79A2 and Bacterial Aldoxime Dehydratase

The biosynthetic pathway for the production of phenylacetonitrile (PAN), which has a wide variety of uses in chemical and pharmaceutical industries, was constructed in Escherichia coli utilizing enzymes from the plant glucosinolate-biosynthetic and bacterial aldoxime-nitrile pathways. First, the single-step reaction to produce E,Z-phenylacetaldoxime (PAOx) from l-Phe was constructed in E. coli by introducing the genes encoding cytochrome P450 (CYP) 79A2 and CYP reductase from Arabidopsis thaliana, yielding the E,Z-PAOx-producing transformant. Second, this step was expanded to the production of PAN by further introducing the aldoxime dehydratase (Oxd) gene from Bacillus sp. strain OxB-1, yielding the PAN-producing transformant. The E,Z-PAOx-producing transformant also produced phenethyl alcohol and PAN as by-products, which were suggested to be the metabolites of E,Z-PAOx produced by E. coli enzymes, while the PAN-producing transformant accumulated only PAN in the culture broth, which suggested that the CYP79A2 reaction (the conversion of l-Phe to E,Z-PAOx) was a potential bottleneck in the PAN production pathway. Expression of active CYP79A2 and concentration of biomass were improved by the combination of the autoinduction method, coexpression of groE, encoding the heat shock protein GroEL/GroES, N-terminal truncation of CYP79A2, and optimization of the culture conditions, yielding a >60-fold concentration of E,Z-PAOx (up to 2.9 mM). The concentration of PAN was 4.9 mM under the optimized conditions. These achievements show the potential of this bioprocess to produce nitriles and nitrile derivatives in the absence of toxic chemicals.