Mechanistic basis for the evolution of chalcone synthase catalytic cysteine reactivity in land plants
Mechanistic basis for the evolution of chalcone synthase catalytic cysteine reactivity in land plants
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DOI：
10.1074/jbc.ra118.005695
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发表时间：
2018-11-30
影响因子：
4.8
通讯作者：
Weng, Jing-Ke
中科院分区：
文献类型：
--
作者：
Liou, Geoffrey;Chiang, Ying-Chih;Weng, Jing-Ke
黄酮类化合物是一种重要的多酚类天然产物，广泛存在于陆生植物中，在植物的生态位中发挥着多种功能，包括保护紫外线、吸引传粉者、共生固氮和防御食草动物等。查尔酮合成酶（Chalcone synthase，CHS）是植物类黄酮合成的第一步，在陆生植物中高度保守。在几个先前报道的晶体结构的CHS从开花植物，催化半胱氨酸被氧化为亚磺酸，表明增强的亲核性在这个残基与其增加的敏感性氧化。在这项研究中，我们报告了一组新的晶体结构的CHSs代表所有五个主要的谱系的陆地植物（苔藓植物，石松，念珠藻，裸子植物，被子植物），跨越5亿年的进化。我们发现，从石松和苔藓物种的CHS的结构保存在还原状态的催化半胱氨酸，在对比中看到的半胱氨酸亚磺酸在所有的Euphyl-lophyte CHS结构。在体内互补，在体外生物化学和诱变分析，分子动力学模拟确定了一组不同的残基之间的基底植物和euphyllophyte CHSs和调节催化半胱氨酸的反应性。我们建议，CHS活性位点的环境已经演变在nephyllophytes进一步提高催化半胱氨酸的亲核性，因为分歧的nephyllophytes从其他维管植物谱系4亿年前。CHS的这些变化可能导致了真叶植物类黄酮生物合成的多样化，这反过来又导致了它们在陆地生态系统中的优势地位。
Flavonoids are important polyphenolic natural products, ubiquitous in land plants, that play diverse functions in plants' survival in their ecological niches, including UV protection, pigmentation for attracting pollinators, symbiotic nitrogen fixation, and defense against herbivores. Chalcone synthase (CHS) catalyzes the first committed step in plant flavonoid biosynthesis and is highly conserved in all land plants. In several previously reported crystal structures of CHSs from flowering plants, the catalytic cysteine is oxidized to sulfinic acid, indicating enhanced nucleophilicity in this residue associated with its increased susceptibility to oxidation. In this study, we report a set of new crystal structures of CHSs representing all five major lineages of land plants (bryophytes, lycophytes, monilophytes, gymnosperms, and angiosperms), spanning 500 million years of evolution. We reveal that the structures of CHS from a lycophyte and a moss species preserve the catalytic cysteine in a reduced state, in contrast to the cysteine sulfinic acid seen in all euphyl-lophyte CHS structures. In vivo complementation, in vitro biochemical and mutagenesis analyses, and molecular dynamics simulations identified a set of residues that differ between basal-plant and euphyllophyte CHSs and modulate catalytic cysteine reactivity. We propose that the CHS active-site environment has evolved in euphyllophytes to further enhance the nucleophilicity of the catalytic cysteine since the divergence of euphyllophytes from other vascular plant lineages 400 million years ago. These changes in CHS could have contributed to the diversification of flavonoid biosynthesis in euphyllophytes, which in turn contributed to their dominance in terrestrial ecosystems.