Department of Biochemistry and Molecular Biology A, Faculty of Biology, Regional Campus of International Excellence, Campus Mare Nostrum, University of Murcia, Murcia, Spain.
Cereal Research Program, National Agricultural University La Molina, Lima, Peru.
J Exp Bot. 2022 Jun 24;73(12):4170-4183. doi: 10.1093/jxb/erac151.
Chenopodium quinoa (quinoa) is a pseudo-cereal that forms part of the cultural heritage of Andean countries, and its grains have high nutritional value and potential health benefits. Betalains are nitrogenous water-soluble pigments and bioactive molecules that contribute to these health-promoting properties. Betalains are restricted to plants of the order Caryophyllales, to which quinoa belongs. A new family of betalains has been discovered in the form of unconventional decarboxylated pigments. Here, we show that these pigments accumulate in ripening quinoa grains of fluorescent nature, and are putatively based on a dopamine-cleaving activity. This study describes for the first time the purification and molecular and functional characterization of a 4,5-dopamine extradiol dioxygenase enzyme from plants. It is a monomeric protein with a molecular mass of 34.5 kDa characterized by chromatography, electrophoresis, and time-of-flight mass spectrometry. We demonstrate that this key enzyme has a dual function in a square-shaped biosynthetic pathway towards the formation of both carboxylated and decarboxylated pigments. Enzyme kinetic properties are characterized for the production of 6-decarboxy-betalamic acid and 3,4-dihydroxy-l-phenylalanine-derived betalamic acid, the two structural units of plant pigment in nature. The profile of multiple betalains present in quinoa grains has been reproduced in one-pot bioreactors containing the novel enzyme and two competing substrates.
藜麦（藜麦）是一种伪谷物，是安第斯国家文化遗产的一部分，其谷物具有很高的营养价值和潜在的健康益处。甜菜碱是含氮的水溶性色素和生物活性分子，有助于发挥这些促进健康的特性。甜菜碱仅限于藜科植物，藜麦属于藜科植物。以非传统脱羧色素形式发现了甜菜碱的一个新家族。在这里，我们表明这些色素在成熟的荧光藜麦谷物中积累，并假定基于多巴胺裂解活性。本研究首次描述了一种来自植物的 4,5-多巴胺外二醇加氧酶的纯化以及分子和功能特征。它是一种单体蛋白，分子量为 34.5 kDa，通过色谱、电泳和飞行时间质谱进行了表征。我们证明，这种关键酶在方形生物合成途径中具有双重功能，可形成羧基化和脱羧基化色素。酶动力学特性用于生产 6-脱羧基-甜菜碱酸和 3,4-二羟基-l-苯丙氨酸衍生的甜菜碱酸，这是天然植物色素的两个结构单元。在含有新型酶和两种竞争底物的一锅式生物反应器中重现了存在于藜麦谷物中的多种甜菜碱的特征。
