Department of Plant Pathology, Kansas State University, Manhattan KS, 66506, U.S.A.
Essays Biochem. 2023 Sep 13;67(5):865-876. doi: 10.1042/EBC20230003.
Branched-chain amino acids (BCAAs)-isoleucine, leucine, and valine-are synthesized by fungi. These amino acids are important components of proteins and secondary metabolites. The biochemical pathway for BCAA biosynthesis is well-characterized in the yeast Saccharomyces cerevisiae. The biosynthesis of these three amino acids is interconnected. Different precursors are metabolized in multiple steps through shared enzymes to produce isoleucine and valine, and the valine biosynthesis pathway branches before the penultimate step to a series of leucine biosynthesis-specific steps to produce leucine. Recent efforts have made advances toward characterization of the BCAA biosynthesis pathway in several fungi, revealing diversity in gene duplication and functional divergence in the genes for these enzymatic steps in different fungi. The BCAA biosynthesis pathway is regulated by the transcription factor LEU3 in S. cerevisiae, and LeuB in Aspergillus nidulans and Aspergillus fumigatus, and the activity of these transcription factors is modulated by the leucine biosynthesis pathway intermediate α-isopropylmalate. Herein, we discuss recent advances in our understanding of the BCAA pathway and its regulation, focusing on filamentous ascomycete fungi and comparison with the well-established process in yeast.
支链氨基酸（BCAAs） - 异亮氨酸、亮氨酸和缬氨酸 - 由真菌合成。这些氨基酸是蛋白质和次生代谢物的重要组成部分。在酵母酿酒酵母中，BCAA 生物合成的生化途径得到了很好的描述。这三种氨基酸的生物合成是相互关联的。不同的前体通过共享酶在多个步骤中代谢，产生异亮氨酸和缬氨酸，而缬氨酸生物合成途径在倒数第二步之前分支，进入一系列产生亮氨酸的特异性步骤。最近的研究进展揭示了几种真菌中 BCAA 生物合成途径的特征，揭示了不同真菌中这些酶步骤的基因重复和功能分化的多样性。BCAA 生物合成途径在酿酒酵母中由转录因子 LEU3 调控，在构巢曲霉和烟曲霉中由 LeuB 调控，这些转录因子的活性受到亮氨酸生物合成途径中间产物α-异丙基苹果酸的调节。本文讨论了我们对 BCAA 途径及其调控的理解的最新进展，重点是丝状子囊菌真菌，并与酵母中已建立的过程进行了比较。
