Abstract
Omega-3 long chain polyunsaturated fatty acids (ω3 LC-PUFAs) such as eicosapentaenoic acid (EPA; 20:5ω3) and docosahexaenoic acid (DHA; 22:6ω3) are important fatty acids for human health. These ω3 LC-PUFAs are produced from their ω3 precursors by a set of desaturases and elongases involved in the biosynthesis pathway and are also converted from ω6 LC-PUFA by omega-3 desaturases (ω3Ds). Here, we have investigated eight ω3-desaturases obtained from a cyanobacterium, plants, fungi and a lower animal species for their activities and compared their specificities for various C18, C20 and C22 ω6 PUFA substrates by transiently expressing them in Nicotiana benthamiana leaves. Our results showed hitherto unreported activity of many of the ω3Ds on ω6 LC-PUFA substrates leading to their conversion to ω3 LC-PUFAs. This discovery could be important in the engineering of EPA and DHA in heterologous hosts.
Highlights
Long chain polyunsaturated fatty acids such as arachidonic acid (ARA; 20:4ω6), eicosapentaenoic acid (EPA; 20:5ω3) and docosahexaenoic acid (DHA; 22:6ω3) are essential fatty acids for human health
Arachidonic acid is mainly located in the brain, skeletal muscles and liver, while EPA and DHA are rich in the brain, retina and skin
Beneficial effects on infant growth and development have been shown for ω6 LC-PUFAs such as ARA, but they have been associated with blood coagulating and pain initiating properties, whereas ω3 LC-PUFAs have anti-thrombotic and anti-inflammatory properties
Summary
Long chain polyunsaturated fatty acids such as arachidonic acid (ARA; 20:4ω6), eicosapentaenoic acid (EPA; 20:5ω3) and docosahexaenoic acid (DHA; 22:6ω3) are essential fatty acids for human health. The human body produces only a low level of LC-PUFA from the consumption of shorter chained fatty acids from plant and animal sources. The ω3D from an EPA-rich fungus, Saprolgenia diclina, when expressed in yeast, did not recognize C18 substrates and was active only on C20 ω6 fatty acid substrates [11]. The transient expression of exogenous ω3Ds clearly showed higher conversion rates for GLA than the endogenous ω3D in the control and were 55.2 ± 9.7%, 37.3 ± 2.2%, 25.5 ± 6.0%, 15.3 ± 0.6%, 27.2 ± 4.2%. Application of gamma-linolenic acid (GLA) to the ω3D expressing leaf tissues resulted in the production of stearidonic acid, indicating the ω3D activities on another C18 ω6 substrate, GLA (Figure 2). IInntteerreessttiinnggllyy,, CCee--ωω33DD sshhoowweedd ssttrroonngg aaccttiivviittiieessfoforralalltlhtehetetsetesdtedC1C81, 8C,2C0 2a0ndanCd22Cs2u2bssutrbastetrsa, treasn,griannggfirnogmfr5o8m% t5o8%75%to. 7A5m%o. nAgmthoensge tehigehset ωeig3Dhts,ωC3eD-ωs, 3CDe-hωa3dDthheadhitghheehstigchoensvtecrosniovnerrsaitoenforart1e8f:o3ωr 168.:3ω6
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