Formation of conjugated Δ810-double bonds by Δ12-oleic-acid desaturase-related enzymes. Biosynthetic origin of calendic acid

Edgar B. Cahoon, Kevin G. Ripp, Sarah E. Hall, Anthony J. Kinney

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Abstract

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 Δ1113-double bonds by modification of an existing Δ12-double bond in C 18 fatty acids. Here, we report a class of FAD2-related enzymes that modifies a Δ9-double bond to produce the conjugated trans-Δ8, trans-Δ10-double bonds found in calendic acid (18:3Δ8trans, 10trans, 12cis), 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: 2Δ9cis,12cis). 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.

Original languageEnglish (US)
Pages (from-to)2637-2643
Number of pages7
JournalJournal of Biological Chemistry
Volume276
Issue number4
DOIs
StatePublished - Jan 26 2001

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ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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