Formation of Conjugated Δ8,Δ10-Double Bonds by Δ12-Oleic-acid Desaturase-related Enzymes

By E. Cahoon, K. G. Ripp, S. Hall, A. Kinney. Journal of Biological Chemistry, 2001

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Divergent forms of the plant Δ12-oleic-acid desaturase (FAD2) have previously been shown to catalyze the formation of acetylenic bonds, epoxy groups, and conjugated Δ11,Δ13-double bonds by modification of an existing Δ12-double bond in C18 fatty acids. Here, we report a class of FAD2-related enzymes that modifies a Δ9-double bond to produce the conjugatedtrans-Δ8,trans-Δ10-double bonds found in calendic acid (18:3Δ8 trans ,10 trans ,12 cis ), the major component of the seed oil of Calendula officinalis. Using an expressed sequence tag approach, cDNAs for two closely related FAD2-like enzymes, designated CoFADX-1 and CoFADX-2, were identified from a C. officinalis developing seed cDNA library. The deduced amino acid sequences of these polypeptides share 40–50% identity with those of other FAD2 and FAD2-related enzymes. Expression of either CoFADX-1 or CoFADX-2 in somatic soybean embryos resulted in the production of calendic acid. In embryos expressing CoFADX-2, calendic acid accumulated to as high as 22% (w/w) of the total fatty acids. In addition, expression of CoFADX-1 and CoFADX-2 in Saccharomyces cerevisiae was accompanied by calendic acid accumulation when induced cells were supplied exogenous linoleic acid (18:2Δ9 cis ,12 cis ). These results are thus consistent with a route of calendic acid synthesis involving modification of the Δ9-double bond of linoleic acid. Regiospecificity for Δ9-double bonds is unprecedented among FAD2-related enzymes and further expands the functional diversity found in this family of enzymes.

Subfields: Biochemistry, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/960cc98a7be81f51cf5922f318d9820e9d7b51f6

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Co-expression of the borage Δ6 desaturase and the Arabidopsis Δ15 desaturase results in high accumulation of stearidonic acid in the seeds of transgenic soybean (2006, methodology): “FAMES were analyzed by gas chromatography with Xame ionization detection as previously described (Cahoon et al. 2001).”