Delta or Omega? Δ12 (ω6) fatty acid desaturases count 3C after the pre-existing double bond

• Published in: Biochimie 2020-12, Vol.179, p.46-53
• Main Authors: Starikov, Alexander Y., Sidorov, Roman A., Mironov, Kirill S., Goriainov, Sergei V., Los, Dmitry A.
• Format: Article
• Language: English
• Subjects: Desaturation; Fatty acid desaturases; Fatty acids; Gloeobacter violaceus; Synechococcus elongatus; Synechocystis sp. PCC 6803; Δ12-FAD
• ISSN: 0300-9084; 1638-6183
• DOI: 10.1016/j.biochi.2020.09.009

Fatty acid desaturases (FADs) represent a class of oxygen-dependent enzymes that dehydrogenate C–C bonds in the fatty acids (FAs) producing unsaturated CC double bonds that markedly change the properties of biological membranes. FADs are highly specific towards their acyl substrates, the position and configuration of the introduced double bonds. The double bond positioning of soluble acyl-carrier-protein Δ9-FADs was determined relative to the carboxyl end of a FA. Similar mode was suggested for the acyl-lipid Δ12-FADs (also known as ω6-FADs), however, their exact counting order remain unknown. Here we used monounsaturated odd- (17:1Δ10) and even-chain (18:1Δ11) FAs to show that acyl-lipid Δ12-FADs of, at least, two cyanobacterial species, Gloeobacter violaceus and Synechocystis sp. strain PCC 6803, use neither end of the fatty acid (Δ or ω) as a counting reference point; but count three carbons toward the methyl end from an existing double bond in the monoene precursors irrespective of a FA chain length. •Two cyanobacterial acyl-lipid Δ12-FADs were expressed in another cyanobacterium to produce dienoic fatty acids.•Δ12-FADs “count” 3C toward the methyl end from an existing double bond in the monoene precursors.•This counting does not depend on the chain length of a fatty acid.