Cytochrome b 5 Coexpression Increases Tetrahymena thermophila Δ6 Fatty Acid Desaturase Activity in Saccharomyces cerevisiae

Very-long-chain polyunsaturated fatty acids such as arachidonic, eicosapentaenoic, and docosahexaenoic acids, are important to the physiology of many microorganisms and metazoans and are vital to human development and health. The production of these and related fatty acids depends on Δ6 desaturases, the final components of an electron transfer chain that introduces double bonds into 18-carbon fatty acid chains. When a Δ6 desaturase identified from the ciliated protistTetrahymena thermophila was expressed inSaccharomyces cerevisiae cultures supplemented with the 18:2Δ9,12 substrate, only 4% of the incorporated substrate was desaturated. Cytochromeb 5 protein sequences identified from the genome ofT. thermophila included one sequence with two conserved cytochromeb 5 domains. Desaturation by the Δ6 enzyme increased as much as 10-fold whenT. thermophila cytochromeb 5 s were coexpressed with the desaturase. Coexpression of a cytochromeb 5 fromArabidopsis thaliana with the Δ6 enzyme also increased desaturation. A split ubiquitin growth assay indicated that the strength of interaction between cytochromeb 5 proteins and the desaturase plays a vital role in fatty acid desaturase activity, illustrating the importance of protein-protein interactions in this enzyme activity.