Guan Ling-Liang, Hou Kai, Chen Jun-Wen, Xu Ying-Wen, Wu Wei
Sichuan Agricultural University, Wenjiang, China.
Yi Chuan. 2013 May;35(5):643-54. doi: 10.3724/sp.j.1005.2013.00643.
The deduced amino acid sequences characteristics, phylogeny, and functional diverge of ω-6 and ω-3 fatty acid desaturase families were analyzed by using Bioinformatics methods. The results showed that all the deduced amino acid sequences shared three highly conserved histidine rich motifs (Hisbox). All the plastidial ω-6 and ω-3 fatty acid desaturases possessed putative N-terminal signal peptide with different amino acids. A relatively conserved hydrophobic region composed of 10 amino-acid residues was found in the middle of signal peptides, which is presumed to be the functional region of the signal peptide of these enzymes. Most of the plant microsomal ω-6 and ω-3 fatty acid desaturases (FAD2 and FAD3) contained a KKXX-like motif of endoplasmic reticulum (ER) retention signal at the C-terminus. However, no such motif was detected in safflower CtFAD2-3, CtFAD2-4, CtFAD2-5, CtFAD2-6, and CtFAD2-7, while an aromatic aa enriched signal (YKNK) was found at their C-terminus which has been reported to be both necessary and sufficient for maintaining localization of the enzymes in the ER. All the amino acid sequences were divided into four categories through phylogenetic analysis. It was suggested that ω-3 fatty acid desaturase originates in a prokaryotic lineage from ω-6 fatty acid desaturase. Both plastidial and microsomal ω-3 fatty acid desaturases could be divided into dicotyledonous and monocotyledonous subgroups, which inferred that functional differentiation of plastidial and microsomal ω-3 fatty acid desaturases had been formed before the divergence of dicotyledonous and monocotyledonous plants. Seed type and housekeeping type FAD2 diverged after the formation of dicotyledonous plants. Except for plant FAD3/plant FAD2, posterior probability values over 0.80 amino acid sites were identified among the functional differentiation subsets, which were mainly distributed at the front and back end of Hisbox I, and the front end of Hisbox II. This indicated that the variations of these amino acid sites played an important role in the size and conformation of protein functional domains and subfamily functional divergence.
运用生物信息学方法分析了ω-6和ω-3脂肪酸去饱和酶家族推导的氨基酸序列特征、系统发育及功能差异。结果表明，所有推导的氨基酸序列均具有三个高度保守的富含组氨酸基序（Hisbox）。所有质体ω-6和ω-3脂肪酸去饱和酶都具有含不同氨基酸的推定N端信号肽。在信号肽中部发现了一个由10个氨基酸残基组成的相对保守的疏水区域，推测这是这些酶信号肽的功能区。大多数植物微粒体ω-6和ω-3脂肪酸去饱和酶（FAD2和FAD3）在C端含有内质网（ER）滞留信号的KKXX样基序。然而，在红花CtFAD2-3、CtFAD2-4、CtFAD2-5、CtFAD2-6和CtFAD2-7中未检测到此类基序，而在它们的C端发现了一个富含芳香族氨基酸的信号（YKNK），据报道该信号对于维持酶在内质网中的定位既必要又充分。通过系统发育分析，所有氨基酸序列被分为四类。提示ω-3脂肪酸去饱和酶起源于ω-6脂肪酸去饱和酶的原核谱系。质体和微粒体ω-3脂肪酸去饱和酶均可分为双子叶和单子叶亚组，这表明质体和微粒体ω-3脂肪酸去饱和酶的功能分化在双子叶和单子叶植物分化之前就已形成。种子型和管家型FAD2在双子叶植物形成后发生分化。除了植物FAD3/植物FAD2外，在功能分化亚组中鉴定出后验概率值超过0.80的氨基酸位点，这些位点主要分布在Hisbox I的前端和后端以及Hisbox II的前端。这表明这些氨基酸位点的变异在蛋白质功能域的大小和构象以及亚家族功能分化中起重要作用。
