Dahmen Jeremy L, Olsen Rebecca, Fahy Deirdre, Wallis James G, Browse John
Institute of Biological Chemistry Washington State University, Pullman, Washington, USA.
Eukaryot Cell. 2013 Jun;12(6):923-31. doi: 10.1128/EC.00332-12. Epub 2013 Apr 12.
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 protist Tetrahymena thermophila was expressed in Saccharomyces cerevisiae cultures supplemented with the 18:2(Δ9,12) substrate, only 4% of the incorporated substrate was desaturated. Cytochrome b₅ protein sequences identified from the genome of T. thermophila included one sequence with two conserved cytochrome b₅ domains. Desaturation by the Δ6 enzyme increased as much as 10-fold when T. thermophila cytochrome b₅s were coexpressed with the desaturase. Coexpression of a cytochrome b₅ from Arabidopsis thaliana with the Δ6 enzyme also increased desaturation. A split ubiquitin growth assay indicated that the strength of interaction between cytochrome b₅ proteins and the desaturase plays a vital role in fatty acid desaturase activity, illustrating the importance of protein-protein interactions in this enzyme activity.
超长链多不饱和脂肪酸，如花生四烯酸、二十碳五烯酸和二十二碳六烯酸，对许多微生物和后生动物的生理功能很重要，对人类发育和健康也至关重要。这些脂肪酸及相关脂肪酸的产生取决于Δ6去饱和酶，它是将双键引入18碳脂肪酸链的电子传递链的最终组成部分。当在添加了18:2(Δ9,12)底物的酿酒酵母培养物中表达从纤毛虫嗜热栖热菌中鉴定出的Δ6去饱和酶时，只有4%的掺入底物被去饱和。从嗜热栖热菌基因组中鉴定出的细胞色素b₅蛋白序列包括一个具有两个保守细胞色素b₅结构域的序列。当嗜热栖热菌细胞色素b₅与去饱和酶共表达时，Δ6酶的去饱和作用增加了多达10倍。拟南芥的细胞色素b₅与Δ6酶共表达也增加了去饱和作用。一种分裂泛素生长试验表明，细胞色素b₅蛋白与去饱和酶之间相互作用的强度在脂肪酸去饱和酶活性中起着至关重要的作用，说明了蛋白质-蛋白质相互作用在这种酶活性中的重要性。
