Functional Identification of Two Types of Carotene Hydroxylases from the Green Alga Dunaliella bardawil Rich in Lutein

作者：Liang, Ming-Hua; Xie, Hong; Chen, Hao-Hong; Liang, Zhi-Cong; Jiang, Jian-Guo^*

来源：ACS Synthetic Biology, 2020, 9(6): 1246-1253.

DOI：10.1021/acssynbio.0c00070

• carotene hydroxylase
• CYP97
• carotenoid
• Dunaliella bardawil
• functional complementation

The salt-tolerant unicellular alga Dunaliella bardawil FACHB-847 can accumulate large amounts of lutein, but the underlying cause of massive accumulation of lutein is still unknown. In this study, genes encoding two types of carotene hydroxylases, i.e., beta-carotene hydroxylase (DbBCH) and cytochrome P450 carotenoid hydroxylase (DbCYP97s; DbCYP97A, DbCYP97B, and DbCYP97C), were cloned from D. bardawil. Their substrate specificities and enzyme activities were tested through functional complementation assays in Escherichia coli. It was showed that DbBCH could catalyze the hydroxylation of the beta-rings of both beta- and alpha-carotene, and displayed a low level of epsilon-hydroxylase. Unlike CYP97A from higher plants, DbCYP97A could not hydroxylate beta-carotene. DbCYP97A and DbCYP97C showed high hydroxylase activity toward the beta-ring and epsilon-ring of alpha-carotene, respectively. DbCYP97B displayed minor activity toward the beta-ring of alpha-carotene. The high accumulation of lutein in D. bardawil may be due to the multiple pathways for lutein biosynthesis generated from alpha-carotene with zeinoxanthin or alpha-cryptoxanthin as intermediates by DbBCH and DbCYP97s. Taken together, this study provides insights for understanding the underlying reason for high production of lutein in the halophilic green alga D. bardawil FACHB-847.