Escalera-Fanjul Ximena, Campero-Basaldua Carlos, Colón Maritrini, González James, Márquez Dariel, González Alicia
Instituto de Fisiología Celular, Departamento de Bioquímica y Biología Estructural, Universidad Nacional Autónoma de MéxicoMexico City, Mexico.
Front Microbiol. 2017 Jun 26;8:1150. doi: 10.3389/fmicb.2017.01150. eCollection 2017.
Gene duplication is one of the major evolutionary mechanisms providing raw material for the generation of genes with new or modified functions. The yeast originated after an allopolyploidization event, which involved mating between two different ancestral yeast species. and codify proteins with 65% identity, which were proposed to be paralogous alanine transaminases. Further analysis of their physiological role showed that while encodes an alanine transaminase which constitutes the main pathway for alanine biosynthesis and the sole pathway for alanine catabolism, Alt2 does not display alanine transaminase activity and is not involved in alanine metabolism. Moreover, phylogenetic studies have suggested that and come from each one of the two parental strains which gave rise to the ancestral hybrid. The present work has been aimed to the understanding of the properties of the ancestral type and , alanine transaminases in order to better understand the and evolutionary history. These ancestral -type species were chosen since they harbor genes, which are related to Presented results show that, although and constitute orthologous genes, encoding alanine transaminases, both yeasts display Alt1 and Alt1 independent alanine transaminase activity and additional unidentified alanine biosynthetic and catabolic pathway(s). Furthermore, phenotypic analysis of null mutants uncovered the fact that Alt1 and Alt1 have an additional role, not related to alanine metabolism but is necessary to achieve wild type growth rate. Our study shows that the ancestral alanine transaminase function has been retained by the encoded enzyme, which has specialized its catabolic character, while losing the alanine independent role observed in the ancestral type enzymes. The fact that Alt2 conserves 64% identity with Alt1 and 66% with Alt1, suggests that Alt2 diversified after the ancestral hybrid was formed. functional diversification resulted in loss of both alanine transaminase activity and the additional alanine-independent Alt1 function, since did not complement the phenotype. It can be concluded that and functional role as alanine transaminases was delegated to , while lost this role during diversification.
基因复制是为具有新功能或修饰功能的基因产生提供原材料的主要进化机制之一。酵母起源于一次异源多倍体化事件，该事件涉及两个不同的祖先酵母物种之间的交配。 和 编码的蛋白质具有65%的同一性，它们被认为是旁系同源丙氨酸转氨酶。对它们生理作用的进一步分析表明， 编码一种丙氨酸转氨酶，它构成了丙氨酸生物合成的主要途径和丙氨酸分解代谢的唯一途径，而Alt2不显示丙氨酸转氨酶活性，也不参与丙氨酸代谢。此外，系统发育研究表明， 和 分别来自产生祖先杂种的两个亲本菌株中的一个。目前的工作旨在了解祖先类型的 和 丙氨酸转氨酶的特性，以便更好地理解 和 的进化历史。选择这些祖先类型的物种是因为它们含有与 相关的 基因。呈现的结果表明，尽管 和 构成了直系同源基因，编码丙氨酸转氨酶，但两种酵母都显示出Alt1和不依赖Alt1的丙氨酸转氨酶活性以及其他未鉴定的丙氨酸生物合成和分解代谢途径。此外，对缺失突变体的表型分析揭示了这样一个事实，即Alt1和Alt1具有额外的作用，与丙氨酸代谢无关，但对于达到野生型生长速率是必要的。我们的研究表明，祖先丙氨酸转氨酶的功能由 编码的酶保留下来，该酶专门化了其分解代谢特性，同时失去了在祖先类型酶中观察到的不依赖丙氨酸的作用。Alt2与Alt1具有64%的同一性，与Alt1具有66%的同一性，这一事实表明Alt2在祖先杂种形成后发生了分化。 功能多样化导致丙氨酸转氨酶活性和额外的不依赖丙氨酸的Alt1功能丧失，因为 不能互补 表型。可以得出结论， 和 作为丙氨酸转氨酶的功能被赋予了 ，而 在分化过程中失去了这一功能。
