A novel Delta9 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 Delta12, Delta15, Delta9, and Delta6 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 Delta9 desaturase, designated desC1 and desC2, from Nostoc species. The desC1 gene is highly similar to the desC gene that encodes a Delta9 desaturase that acts on C18 fatty acids at the sn-1 position. Homologues of desC2 are found in genomes of cyanobacterial species in which Delta9-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 Delta9 acyl-lipid desaturase that acts on fatty acids esterified to the sn-2 position of glycerolipids.

Figure 1. Alignment of the complete deduced amino acid sequences of DesC1 and DesC2 of cyanobacteria, grouped on the basis of the distribution of fatty acids at sn− positions

Amino acid residues that are conserved in DesC2 are highlighted in black boxes.The eight domains that are conserved in DesC2 are indicated by square brackets. The deduced amino acid sequences were obtained from databases (GenBank®, EMBL and DDBJ) and the sequences were aligned using CLUSTAL W version 1.83 software. The accession number of each DesC sequence and the name of corresponding cyanobacterium are indicated on the left.

Figure 1. Alignment of the complete deduced amino acid sequences of DesC1 and DesC2 of cyanobacteria, grouped on the basis of the distribution of fatty acids at sn− positions

Amino acid residues that are conserved in DesC2 are highlighted in black boxes.The eight domains that are conserved in DesC2 are indicated by square brackets. The deduced amino acid sequences were obtained from databases (GenBank®, EMBL and DDBJ) and the sequences were aligned using CLUSTAL W version 1.83 software. The accession number of each DesC sequence and the name of corresponding cyanobacterium are indicated on the left.

Figure 1. Alignment of the complete deduced amino acid sequences of DesC1 and DesC2 of cyanobacteria, grouped on the basis of the distribution of fatty acids at sn− positions

Amino acid residues that are conserved in DesC2 are highlighted in black boxes.The eight domains that are conserved in DesC2 are indicated by square brackets. The deduced amino acid sequences were obtained from databases (GenBank®, EMBL and DDBJ) and the sequences were aligned using CLUSTAL W version 1.83 software. The accession number of each DesC sequence and the name of corresponding cyanobacterium are indicated on the left.

Figure 2. Phylogenetic tree determined on the basis of deduced amino acid sequences of DesC homologues in cyanobacteria

The amino acids sequences corresponding to the desC genes in cyanobacteria were obtained from databases (GenBank, EMBL and DDBJ) and the sequences were aligned with CLUSTAL W version 1.83 (as shown in Figure 1). The phylogenetic tree was drawn with NJjplot (http://pbil.univ-lyon1.fr/software/njplot.html) using PHYLIP (phylogeny inference package) version 3.5c. The accession number of each desC homologue is indicated beside the name of the corresponding cyanobacterium. Bootstrap values (expressed relative to 1000 replications; [3]) are given at the respective nodes.