Departamento de Biología Molecular y Bioquímica, Universidad de Málaga. Edificio I+D, Málaga 29071, Spain.
Departamento de Genómica y Proteómica, Instituto de Biomedicina de Valencia, CSIC, Unidad de Enzimopatología Estructural, Valencia 46010, Spain.
Plant Physiol. 2022 Jan 20;188(1):134-150. doi: 10.1093/plphys/kiab454.
Phenylalanine (Phe) is the precursor of essential secondary products in plants. Here we show that a key, rate-limiting step in Phe biosynthesis, which is catalyzed by arogenate dehydratase, experienced feedback de-regulation during evolution. Enzymes from microorganisms and type-I ADTs from plants are strongly feedback-inhibited by Phe, while type-II isoforms remain active at high levels of Phe. We have found that type-II ADTs are widespread across seed plants and their overproduction resulted in a dramatic accumulation of Phe in planta, reaching levels up to 40 times higher than those observed following the expression of type-I enzymes. Punctual changes in the allosteric binding site of Phe and adjacent region are responsible for the observed relaxed regulation. The phylogeny of plant ADTs evidences that the emergence of type-II isoforms with relaxed regulation occurred at some point in the transition between nonvascular plants and tracheophytes, enabling the massive production of Phe-derived compounds, primarily lignin, a hallmark of vascular plants.
苯丙氨酸（Phe）是植物中必需次生产物的前体。在这里，我们表明，苯丙氨酸生物合成中的一个关键限速步骤，由芳香族氨基酸脱氨酶（arogenate dehydratase）催化，在进化过程中经历了反馈调节失活。微生物中的酶和植物中的 I 型 ADTs 受到 Phe 的强烈反馈抑制，而 II 型同工酶在高 Phe 水平下仍保持活性。我们发现，II 型 ADTs 在种子植物中广泛存在，它们的过度表达导致 Phe 在植物体内的大量积累，达到比表达 I 型酶时观察到的水平高 40 倍的水平。Phe 和相邻区域的变构结合位点的点突变负责观察到的调节放松。植物 ADTs 的系统发育证据表明，在非维管束植物和木质部植物之间的过渡时期，出现了调节放松的 II 型同工酶，从而能够大量产生 Phe 衍生的化合物，主要是木质素，这是维管束植物的特征。
