Site-directed mutagenesis of histidine residues in the Δ12 acyl-lipid desaturase of Synechocystis

AbstractIn the cyanobacterium Synechocystis sp. PCC 6803, there are four acyl-lipid desaturases that are, respectively, specific to the Δ6, Δ9, Δ12 and ω3 positions of fatty acids. The desA gene for the Δ12 acyl-lipid desaturase was modified by site-directed mutagenesis, such that four of the histidine residues that are conserved in the four desaturases and one histidine residue that is not conserved were replaced by arginine, and the mutated desA genes were overexpressed in Escherichia coli. All of these mutations eliminated the Δ12 desaturase activity. These results demonstrate that the five histidine residues are essential for the activity of the Δ12 desaturase, perhaps by providing the ligands for the catalytic Fe center