陆地棉KASⅡ酶蛋白结构分析

Protein Structure Analysis of a KASⅡ Enzyme in Gossypium hirsutum

β-酮脂酰-ACP合成酶Ⅱ(KASⅡ)(EC:2.3.1.179)是控制植物细胞脂肪酸合成和16C与18C脂肪酸比值的关键酶,亦是植物油脂代谢修饰的分子靶标。应用基因组学分析工具从陆地棉(Gossypium hirsutum)基因组鉴定获得一个与已知KASⅡ高度同源的棉花KASⅡ基因GhKASⅡ,编码576个氨基酸肽链,其分子量为61.8 k Da,理论等电点为8.83。蛋白结构预测分析显示,GhKASⅡ蛋白为可溶性酶蛋白,具有质体转运肽,定位于质体中;GhKASⅡ蛋白二级结构主要形式为α-螺旋(32.99%)和无规则卷曲(36.63%)。3D结构模拟表明,GhKASⅡ蛋白为同源二聚体,由2个相同的亚基构成,空间构型为紧密的心形结构。蛋白序列多重比对发现,GhKASⅡ与雷蒙德氏棉、亚洲棉、可可树的KASⅡ蛋白亲缘关系较近,植物KASⅡ蛋白C端保守性高,N端变异大。GhKASⅡ蛋白保守的酶催化活性域位于318~334位(氨基酸残基),其关键酶活位点是位于327位的半胱氨酸。研究结果可为深入解析棉花等油料作物的脂肪酸生物合成机制及油脂遗传改良提供科学参考。

β-ketoacyl-ACP synthase Ⅱ（KASⅡ）（EC： 2.3.1.179）is a key enzyme responsible for fatty acid synthesis and the ratio of16C/18 C fatty acid in plant cells. It is also the molecular target for lipid metabolism modification. In this study, genomics analysis tools were employed to obtain a Gh KASⅡ gene from upland cotton（Gossypium hirsutum）genome, which was highly homologous to the known KASⅡ genes. Gh KASⅡ gene encoded 576-amino acid peptide with a predicted molecular mass of about 61.8 k Da and a PI of 8.83.Protein structure prediction showed that Gh KASⅡ protein was a soluble protein with a plastid transit peptide, and located in the plastid.Secondary structure of Gh KASⅡ were made up of α-helices（32.99%）and random coils（36.63%）. Three-dimensional（3D）structure modeling revealed that the Gh KASⅡ protein was a homodimer consisting of two same subunits, and the spatial configuration was a tightly heart-shaped structure. Multiple sequence alignment showed that Gh KASⅡ was much closely to the KASⅡ proteins from Raymond cotton, Asian cotton and cacao tree evolutionally. The C-terminus of KASⅡ proteins was highly conserved whereas N-terminus was highly variable. The enzyme-active domain of Gh KASⅡ protein was located between 318 and 334 amino acid residues with the conserved Cys（327） as the key active site. The results of the study will provide a scientific reference for further understanding the fatty acid biosynthesis mechanism and genetic improvement of cotton and other oil crops.