A novel Δ9 acyl-lipid desaturase, DesC2, from cyanobacteria acts on fatty acids esterified to the sn−2 position of glycerolipids

Abstract

Acyl-lipid desaturases are enzymes that convert a C–C single bond into a C=C double bond in fatty acids that are esterified to membrane-bound glycerolipids. Four types of acyl-lipid desaturase, namely DesA, DesB, DesC, and DesD, acting at the Δ12, Δ15, Δ9, and Δ6 positions of fatty acids respectively, have been characterized in cyanobacteria. These enzymes are specific for fatty acids bound to the sn−1 position of glycerolipids. In the present study, we have cloned two putative genes for a Δ9 desaturase, designated desC1 and desC2, from Nostoc species. The desC1 gene is highly similar to the desC gene that encodes a Δ9 desaturase that acts on C18 fatty acids at the sn−1 position. Homologues of desC2 are found in genomes of cyanobacterial species in which Δ9-desaturated fatty acids are esterified to the sn−2 position. Heterologous expression of the desC2 gene in Synechocystis sp. PCC 6803, in which a saturated fatty acid is found at the sn−2 position, revealed that DesC2 could desaturate this fatty acid at the sn−2 position. These results suggest that the desC2 gene is a novel gene for a Δ9 acyl-lipid desaturase that acts on fatty acids esterified to the sn-2 position of glycerolipids.