Δ^6-脂肪酸脱氢酶的系统进化分析

A phylogenetic analysis of Δ^6-fatty acid desaturases

将已报道的Δ6-脂肪酸脱氢酶基因所编码的氨基酸序列进行比较,推断它们的系统进化关系.分析结果显示的Δ6-脂肪酸脱氢酶氨基酸序列都具有3个高度保守的组氨酸富集区,表明它们具有共同起源,并分为原核、动物、高等植物和低等真核4个类型.推测原核类型的Δ6-脂肪酸脱氢酶是所有Δ6-脂肪酸脱氢酶的共同祖先,真核类型的Δ6-脂肪酸脱氢酶在后来的进化中形成更具选择优势的细胞色素b5融合蛋白.动物类型的Δ6-脂肪酸脱氢酶处于真核类Δ6-脂肪酸脱氢酶的最基础分枝,其中鱼类的Δ6-脂肪酸脱氢酶可能是动物类型的Δ6-脂肪酸脱氢酶通过序列改变向Δ5-脂肪酸脱氢酶进化的中间过度形式.高等植物和真菌类型的Δ6-脂肪酸脱氢酶存在着共同起源,藻类和苔藓可能在高等植物和真菌类Δ6-脂肪酸脱氢酶的进化关系上扮演着重要的角色.线虫的Δ6-脂肪酸脱氢酶作为一个独立而且最基础的分枝位于低等真核单系组中,它可能是一种趋同进化的结果.

The deduced amino acid equence were compared for infering their phylogenetic relationship. These deduced amino acid sequence were coded by the Δ^6-fiatty acid desaturase genes which were reported before. The resuts show that all the deduced amino acid sequence have three highly conservative histidine-rich moti{s. This indicates the decuced amino acid sequence probably have common origin. The Δ^6-fatty acid desaturaes can by divided into prokaryotic, animal, high plant and eukaryotic Δ^6-fatty acid desaturases. It is infered thatthe prokaryotic Δ^6-fatty acid desaturases are the ancestors for all the Δ^6-fatty acid desaturases. However, during the evolution period, the cukaryotic Δ^6-fatty acid from a cytochrome b5 protein. The cytochrome b5 protein（domain） probably can provide a prior selection by increasing the electron transport efficiency during the unsaturation reaction. The animal Δ^6-fatty acid desaturases are the most basal branch of eukaryotic Δ^6-fatty acid desaturases. The Δ^6-fatty acid desaturases from finshes maybe are the transition state between animal Δ^6-fatty acid desaturase and AS-fatty acid desaturase. The low eukaryotic and high plant Δ^6-fatty acid desaturases are separated. This indicats they probably have a same origin. Moreover, Δ^6-fatty acid desaturases from moss and algae maybe play an significant role in the evolution relationship between low eukaryotic Δ^6-fatty acid desaturases and high plant Δ^6-fatty acid desaturases. The Δ^6-fatty acid desaturased from Caenorhabdits elegcms is a separate and primary branch in the evolution tree, and belongs to be low eukaryatic enzymes. This indicates that it probably is the result of a convergent evolution.