Desaturase Module

After absorption of exogenous fatty acids from the environment, the enzymes, Δ9- Δ12-and Δ15-desaturases catalyze the conversion of fatty acids (stearic acid) into α-linolenic acid, ALA (Qiu, 2002). Because E. coli originally lacks the genes encoding the desaturases, we have to construct and transform the recombinant DNA plasmid containing them into E. coli..

The gene sequences of the three desaturases can be obtained from Synechocystis, and optimized for expression in E. coli. After transformation of the constructed plasmid, the bacterium is able to produce the corresponding enzymes. Δ9 desaturase removes two hydrogen atoms from carbon 9 and carbon 10 of the fatty acid and a double bond will be formed there.

Similarly, Δ12 desaturase works between carbon 12 and carbon 13 while Δ15 desaturase works between carbon 15 and carbon 16. After completion of the reactions, the fatty acid (stearic acid) will be converted into ALA (Figure 1). When ALA is released from E. coli and absorbed by human cells, ALA will be further converted into docosahexaenoic acid, DHA. Since human cells contain genes encoding the remaining desaturases and elongases that are necessary for the conversion of ALA into DHA (Innis, 2007), which is our final target product.

Figure 1. Conversion of stearic acid into α-linolenic acid by three desaturases.

References:

Innis, S. M. (2007). Dietary (n-3) fatty acids and brain development. The Journal of Nutrition. 137: 855.

Qiu, X. (2003). Biosynthesis of docosahenaenoic acid (DHA, 22:6-4, 7, 10, 13, 16, 19): Two distinct pathways. Prostaglandins, Leukotrienes and Essential Fatty Acids. 68(2003): 181-182.