Department of Life Science and Technology, Tokyo Institute of Technology, Yokohama 226-8501, Japan.
Mol Biol Evol. 2022 Aug 3;39(8). doi: 10.1093/molbev/msac164.
The antibiotic alaremycin has a structure that resembles that of 5-aminolevulinic acid (ALA), a universal precursor of porphyrins, and inhibits porphyrin biosynthesis. Genome sequencing of the alaremycin-producing bacterial strain and enzymatic analysis revealed that the first step of alaremcyin biosynthesis is catalysed by the enzyme, AlmA, which exhibits a high degree of similarity to 5-aminolevulinate synthase (ALAS) expressed by animals, protozoa, fungi, and α-proteobacteria. Site-directed mutagenesis of AlmA revealed that the substitution of two amino acids residues around the substrate binding pocket transformed its substrate specificity from that of alaremycin precursor synthesis to ALA synthesis. To estimate the evolutionary trajectory of AlmA and ALAS, we performed an ancestral sequence reconstitution analysis based on a phylogenetic tree of AlmA and ALAS. The reconstructed common ancestral enzyme of AlmA and ALAS exhibited alaremycin precursor synthetic activity, rather than ALA synthetic activity. These results suggest that ALAS evolved from an AlmA-like enzyme. We propose a new evolutionary hypothesis in which a non-essential secondary metabolic enzyme acts as an 'evolutionary seed' to generate an essential primary metabolic enzyme.
抗生素 alaremycin 的结构类似于 5-氨基酮戊酸 (ALA)，ALA 是卟啉的通用前体，并抑制卟啉生物合成。alaremycin 产生菌的基因组测序和酶分析表明，alaremycin 生物合成的第一步由酶 AlmA 催化，该酶与动物、原生动物、真菌和 α-变形菌表达的 5-氨基酮戊酸合酶 (ALAS) 具有高度相似性。AlmA 的定点突变表明，底物结合口袋周围两个氨基酸残基的取代将其底物特异性从 alaremycin 前体合成转变为 ALA 合成。为了估计 AlmA 和 ALAS 的进化轨迹，我们基于 AlmA 和 ALAS 的系统发育树进行了祖先序列重建分析。重建的 AlmA 和 ALAS 的共同祖先酶表现出 alaremycin 前体合成活性，而不是 ALA 合成活性。这些结果表明 ALAS 是从类似 AlmA 的酶进化而来的。我们提出了一个新的进化假设，其中非必需的次生代谢酶充当“进化种子”，产生必需的初生代谢酶。
