Abstract
Background
Thraustochytrids are marine microeukaryotes known for the ability to accumulate high levels of the fatty acid docosahexaenoic acid (DHA, 22:6 n-3). Due to the remarkable benefits of DHA to human health, there is an increasing demand for sustainable DHA sources. Fatty acid profiles are different among several thraustochytrid genera and species. Palmitoleic acid (C16:1 n-7) and vaccenic acid (C18:1 n-7) are synthesized by Aurantiochytrium sp. T66 (T66), but not by Aurantiochytrium limacinum SR21. However, the genome of T66 does not contain proteins homologous to any known Δ9-desaturase, the enzyme converting palmitic acid (C16:0) to C16:1 n-7. Moreover, T66 encodes a protein with a high degree of homology to known Δ12-desaturases. An identical protein from Thraustochytrium sp. ATCC 26185 was shown not to have Δ12-desaturase activity by expression in Escherichia coli (Meesapyodsuk and Qiu, 2016).
Objectives
Since it is important to comprehensively understand the fatty acid synthesis pathways of thraustochytrids to enhance DHA production. In this study, we aimed to identify the enzyme that desaturates the C16:0 fatty acid to C16:1 n-7.
Methods
Heterologous expression of the T66 protein homologous to Δ12-desaturases in A. limacinum SR21 was performed, followed by fatty acid profiling. The potential evolutionary processes of the protein were analyzed by phylogenetic analyses.
Results
We demonstrated that the T66 protein homologous to Δ12-desaturases, is a Δ9-desaturase that synthesizes C16:1 n-7 using C16:0 as a substrate. C18:1 n-7 can then be produced from the elongation of C16:1 n-7. The protein was named T66Des9.The result provides substantial knowledge of the differences of unsaturated fatty acid metabolic pathways among thraustochytrid strains, which is an asset in optimizing strain engineering strategies. Furthermore, T66des9 probably evolved from a Δ12-desaturase-encoding gene, suggesting the prediction of desaturase functions can be challenging without considering potential evolutionary processes, which might affect the interpretation of unsaturated fatty acid metabolic pathways in the organisms of interest.
Thraustochytrids are marine microeukaryotes known for the ability to accumulate high levels of the fatty acid docosahexaenoic acid (DHA, 22:6 n-3). Due to the remarkable benefits of DHA to human health, there is an increasing demand for sustainable DHA sources. Fatty acid profiles are different among several thraustochytrid genera and species. Palmitoleic acid (C16:1 n-7) and vaccenic acid (C18:1 n-7) are synthesized by Aurantiochytrium sp. T66 (T66), but not by Aurantiochytrium limacinum SR21. However, the genome of T66 does not contain proteins homologous to any known Δ9-desaturase, the enzyme converting palmitic acid (C16:0) to C16:1 n-7. Moreover, T66 encodes a protein with a high degree of homology to known Δ12-desaturases. An identical protein from Thraustochytrium sp. ATCC 26185 was shown not to have Δ12-desaturase activity by expression in Escherichia coli (Meesapyodsuk and Qiu, 2016).
Objectives
Since it is important to comprehensively understand the fatty acid synthesis pathways of thraustochytrids to enhance DHA production. In this study, we aimed to identify the enzyme that desaturates the C16:0 fatty acid to C16:1 n-7.
Methods
Heterologous expression of the T66 protein homologous to Δ12-desaturases in A. limacinum SR21 was performed, followed by fatty acid profiling. The potential evolutionary processes of the protein were analyzed by phylogenetic analyses.
Results
We demonstrated that the T66 protein homologous to Δ12-desaturases, is a Δ9-desaturase that synthesizes C16:1 n-7 using C16:0 as a substrate. C18:1 n-7 can then be produced from the elongation of C16:1 n-7. The protein was named T66Des9.The result provides substantial knowledge of the differences of unsaturated fatty acid metabolic pathways among thraustochytrid strains, which is an asset in optimizing strain engineering strategies. Furthermore, T66des9 probably evolved from a Δ12-desaturase-encoding gene, suggesting the prediction of desaturase functions can be challenging without considering potential evolutionary processes, which might affect the interpretation of unsaturated fatty acid metabolic pathways in the organisms of interest.