Enzymatic and physiological characterization of fatty acid activation in Synechocystis sp. PCC6803

Free fatty acids are typically activated by thioesterification processes and catalyzed by the fatty acyl-CoA synthetase or fatty acyl-ACP synthetase. However, the routes for fatty acid activation in cyanobacteria are not well understood. In this investigation, the slr1609 gene, which encodes the fatty acid activation enzyme, was cloned from Synechocystis sp. PCC6803. This gene was identified by heterologous expression and in vitro enzymatic activity analyses. Different from previous reports stating that free fatty acids are only activated through the fatty acyl-ACP synthetases encoded by these genes in cyanobacteria, this gene was also proven to possess a fatty acyl-CoA synthetase activity, by in vitro enzymatic activity analyses and in vivo complementation experiments. The protein Slr1609 is located in both the cell membrane and the cytosol of Synechocystis sp. PCC6803. The differences in the transcriptional profiles between the wild type and the slr1609 deletion mutant strain were evaluated using microarray analyses. These analyses indicated that 299 differentially expressed genes are involved in fatty acid metabolism, photosynthesis, carbon fixation, stress tolerance and other metabolic processes. Our experiments demonstrate the observed compositional changes in the unsaturated fatty acids from the membrane lipids of the slr1609 deletion mutant when shifted from 30 to 24 °C.