Cloning and characterization of a Δ9-desaturase gene of the Antarctic fish Chionodraco hamatus and Trematomus bernacchii
Chionodraco hamatus and Trematomus bernacchii are perciforms, members of the fish suborder Notothenioidei that live in the Antarctic Ocean and experience very cold and persistent environmental temperature. These fish have biochemical and molecular features that allow them to live at these extreme cold temperatures. Fine tuning of the level of unsaturated fatty acids content in membrane is a key mechanism of living organisms to adapt to cold and high temperatures. Desaturases are key enzymes that synthesize unsaturated fatty acyl-CoAs from saturated fatty acids. We cloned and sequenced a Δ9-desaturase gene and its cDNA of C. hamatus, and the cDNA of T. bernacchii. The coded proteins are virtually identical and share homology to other Δ9-desaturase fish sequences. These proteins contain, in the first trans-membrane domain, two cysteine residues that may form a disulfur bond present in the corresponding membrane region of Δ9-desaturase proteins of other Antarctic fish but not in Eleginops maclovinus that experiences higher environmental temperatures and in all other Δ9-desaturase genes of mammals present in data bases. C. hamatus Δ9-desaturase gene complements a Saccharomyces cerevisiae mutant lacking Δ9-desaturase (Ole1) gene. Analysis of sequence homology of the trans-membrane domains of Δ9-desaturase and the cytoplasmic region of the same proteins of Antarctic fish, non-Antarctic fish and mammals suggest that the significant differences found in the homologous sequences of the first trans-membrane domain may be due to the specific lipid content of their membrane.