Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland 20742, USA.
Plant Cell. 2011 Aug;23(8):3055-69. doi: 10.1105/tpc.111.086827. Epub 2011 Aug 23.
A few species in the genus Adonis are the only land plants known to produce the valuable red ketocarotenoid astaxanthin in abundance. Here, we ascertain the pathway that leads from the β-rings of β-carotene, a carotenoid ubiquitous in plants, to the 3-hydroxy-4-keto-β-rings of astaxanthin (3,3'-dihydroxy-β,β-carotene-4,4'-dione) in the blood-red flowers of Adonis aestivalis, an ornamental and medicinal plant commonly known as summer pheasant's eye. Two gene products were found to catalyze three distinct reactions, with the first and third reactions of the pathway catalyzed by the same enzyme. The pathway commences with the activation of the number 4 carbon of a β-ring in a reaction catalyzed by a carotenoid β-ring 4-dehydrogenase (CBFD), continues with the further dehydrogenation of this carbon to yield a carbonyl in a reaction catalyzed by a carotenoid 4-hydroxy-β-ring 4-dehydrogenase, and concludes with the addition of an hydroxyl group at the number 3 carbon in a reaction catalyzed by the erstwhile CBFD enzyme. The A. aestivalis pathway is both portable and robust, functioning efficiently in a simple bacterial host. Our elucidation of the pathway to astaxanthin in A. aestivalis provides enabling technology for development of a biological production process and reveals the evolutionary origin of this unusual plant pathway, one unrelated to and distinctly different from those used by bacteria, green algae, and fungi to synthesize astaxanthin.
只有少数几个 Adonis 属的物种被认为能够大量产生有价值的红色酮类类胡萝卜素虾青素。在这里，我们确定了从β-胡萝卜素（β-环）到 Adonis aestivalis（一种常见的观赏和药用植物，通常被称为夏牡丹眼）血红色花朵中虾青素（3,3'-二羟基-β，β-胡萝卜素-4,4'-二酮）的 3-羟基-4-酮-β-环的途径，β-胡萝卜素是一种在植物中普遍存在的类胡萝卜素。两种基因产物被发现催化三个不同的反应，该途径的第一和第三反应由同一种酶催化。该途径始于一个β-环的 4 号碳原子的激活，这是由类胡萝卜素β-环 4-脱氢酶（CBFD）催化的反应，然后在该碳原子上进一步脱氢生成羰基，这是由类胡萝卜素 4-羟基-β-环 4-脱氢酶催化的反应，最后在由原来的 CBFD 酶催化的反应中在 3 号碳原子上添加一个羟基。A. aestivalis 途径既便携又稳健，在简单的细菌宿主中高效运行。我们对 A. aestivalis 虾青素途径的阐明为开发生物生产工艺提供了使能技术，并揭示了这种不寻常的植物途径的进化起源，该途径与细菌、绿藻和真菌用于合成虾青素的途径无关，且明显不同。
