Instituto de Nanobiotecnología (NANOBIOTEC), CONICET, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Buenos Aires, Argentina.
Instituto de Biología Molecular y Celular de Rosario, CONICET, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Rosario, Argentina.
J Biol Chem. 2022 Oct;298(10):102397. doi: 10.1016/j.jbc.2022.102397. Epub 2022 Aug 18.
Sterols in eukaryotic cells play important roles in modulating membrane fluidity and in cell signaling and trafficking. During evolution, a combination of gene losses and acquisitions gave rise to an extraordinary diversity of sterols in different organisms. The sterol C-22 desaturase identified in plants and fungi as a cytochrome P-450 monooxygenase evolved from the first eukaryotic cytochrome P450 and was lost in many lineages. Although the ciliate Tetrahymena thermophila desaturates sterols at the C-22 position, no cytochrome P-450 orthologs are present in the genome. Here, we aim to identify the genes responsible for the desaturation as well as their probable origin. We used gene knockout and yeast heterologous expression approaches to identify two putative genes, retrieved from a previous transcriptomic analysis, as sterol C-22 desaturases. Furthermore, we demonstrate using bioinformatics and evolutionary analyses that both genes encode a novel type of sterol C-22 desaturase that belongs to the large fatty acid hydroxylase/desaturase superfamily and the genes originated by genetic duplication prior to functional diversification. These results stress the widespread existence of nonhomologous isofunctional enzymes among different lineages of the tree of life as well as the suitability for the use of T. thermophila as a valuable model to investigate the evolutionary process of large enzyme families.
真核细胞中的甾醇在调节膜流动性以及细胞信号转导和运输中起着重要作用。在进化过程中，基因的丢失和获得的组合导致了不同生物中甾醇的非凡多样性。在植物和真菌中被鉴定为细胞色素 P450 单加氧酶的甾醇 C-22 去饱和酶是从第一个真核细胞色素 P450 进化而来的，并在许多谱系中丢失。尽管纤毛虫 Tetrahymena thermophila 在 C-22 位置使甾醇去饱和，但基因组中不存在细胞色素 P450 直系同源物。在这里，我们旨在确定负责去饱和的基因及其可能的起源。我们使用基因敲除和酵母异源表达方法，从之前的转录组分析中鉴定出两个可能的基因，它们是甾醇 C-22 去饱和酶。此外，我们通过生物信息学和进化分析证明，这两个基因编码一种新型的甾醇 C-22 去饱和酶，属于大型脂肪酸羟化酶/去饱和酶超家族，并且这些基因是在功能多样化之前通过基因复制起源的。这些结果强调了不同生命之树谱系中非同源同功能酶的广泛存在，以及使用 T. thermophila 作为研究大型酶家族进化过程的有价值模型的适用性。
