Sayanova O, Shewry P R, Napier J A
IACR-Long Ashton Research Station, Department of Agricultural Sciences, University of Bristol, Bristol BS41 9AF, United Kingdom.
Plant Physiol. 1999 Oct;121(2):641-6. doi: 10.1104/pp.121.2.641.
Unlike most other plant microsomal desaturases, the Delta6-fatty acid desaturase from borage (Borago officinalis) contains an N-terminal extension that shows homology to the small hemoprotein cytochrome (Cyt) b5. To determine if this domain serves as a functional electron donor for the Delta6-fatty acid desaturase, mutagenesis and functional analysis by expression in transgenic Arabidopsis was carried out. Although expression of the wild-type borage Delta6-fatty acid desaturase resulted in the synthesis and accumulation of Delta6-unsaturated fatty acids, this was not observed in plants transformed with N-terminally deleted forms of the desaturase. Site-directed mutagenesis was used to disrupt one of the axial heme-binding residues (histidine-41) of the Cyt b5 domain; expression of this mutant form of the Delta6-desaturase in transgenic plants failed to produce Delta6-unsaturated fatty acids. These data indicate that the Cyt b5 domain of the borage Delta6-fatty acid desaturase is essential for enzymatic activity.
与大多数其他植物微粒体去饱和酶不同，琉璃苣（Borago officinalis）的Δ6-脂肪酸去饱和酶含有一个N端延伸序列，该序列与小的血红素蛋白细胞色素（Cyt）b5具有同源性。为了确定该结构域是否作为Δ6-脂肪酸去饱和酶的功能性电子供体，通过在转基因拟南芥中表达进行了诱变和功能分析。虽然野生型琉璃苣Δ6-脂肪酸去饱和酶的表达导致了Δ6-不饱和脂肪酸的合成和积累，但在用去饱和酶N端缺失形式转化的植物中未观察到这种情况。定点诱变用于破坏Cyt b5结构域的一个轴向血红素结合残基（组氨酸-41）；这种Δ6-去饱和酶突变形式在转基因植物中的表达未能产生Δ6-不饱和脂肪酸。这些数据表明，琉璃苣Δ6-脂肪酸去饱和酶的Cyt b5结构域对酶活性至关重要。
