氨基酸序列分析揭示苯丙氨酸/酪氨酸解氨酶在陆生植物中的演化

Amino Acid Sequence-based Evolution of Phenylalanine/Tyrosine Ammonia-Lyase in Terrestrial Plants

苯丙烷途径在陆生植物木质素和黄酮类等次生代谢产物的生物合成中至关重要,其中一步必需的反应为苯丙氨酸解氨酶(PAL)将底物苯丙氨酸脱氨催化为下游产物。最新研究发现了能够同时催化苯丙氨酸和酪氨酸脱氨的双功能酶—苯丙氨酸/酪氨酸解氨酶(PTAL),但是对诸多问题,例如怎样精准鉴定PAL和PTAL、植物PAL演化为PTAL其氨基酸序列发生了什么变异、哪些植物类群包含PTAL等,仍属未知。为了探索PAL基因家族在陆生植物中的演化及关键变异,本研究利用PAL氨基酸全长序列构建了陆生植物不同类群系统发育树,比较和分析了PAL和PTAL氨基酸序列并模拟了其蛋白质三维构象。结果表明,以PAL氨基酸序列构建的系统发育树,能够反映已知陆生植物的系统关系,PAL和PTAL的氨基酸序列中存在着8个差异位点,其中121和123这两个关键位点非常稳定,可以联合用于准确鉴定包含PAL和PTAL的植物,并且I121L和F123H的关键变异,导致只能与苯丙氨酸结合的PAL演化为也能同时结合酪氨酸的PTAL。

Phenylpropanoid pathway plays a key role in the biosynthesis of secondary metabolites such as lignin and flavonoids in terrestrial plants.One of the key reactions is the phenylalanine ammonia-lyase(PAL)that catalyzes the deamination of substrate phenylalanine into downstream products to complete the above metabolic synthesis process.A recent study has found a bifunctional phenylalanine/tyrosine ammonia-lyase(PTAL)that can simultaneously catalyze the deamination of both phenylalanine and tyrosine.However,the key differences between PAL and PTAL,and how PTAL evolved from PAL are still unknown.To explore the variation of PAL gene family in the evolution of terrestrial plants and its mechanism to deaminate tyrosine,we compared and analyzed the amino acid sequences of PAL and PTAL,simulated the three-dimensional conformation of their proteins,and constructed a phylogenetic tree of the main groups of terrestrial plants,using the full length of PAL amino acid sequences.Our results showed that the phylogenetic tree of the terrestrial plants constructed by the full length of PAL amino acid sequences could objectively reflect the genetic relationship of the terrestrial plants.In addition,nine different sites in the PAL and PTAL amino acid sequences,among which the 121 and 123 sites were very stable,could be used to identify the terrestrial plant species containing PAL and PTAL.The key variation of I121L and F123H caused the evolution of PAL that only bind phenylalanine into PTAL that could also bind tyrosine.