期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 98, 期 5, 页码 2905-2910出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.051618398
关键词
-
Carotenoids in the photosynthetic membranes of plants typically contain two beta -rings (e.g., beta -carotene and zeaxanthin) or one epsilon- and one beta -ring (e.g., lutein). Carotenoids with two epsilon -rings are uncommon. We reported earlier that the Arabidopsis thaliana lycopene epsilon -cyclase (LCYe) adds one epsilon -ring to the symmetrical linear substrate lycopene, whereas the structurally related lycopene beta -cyclase (LCYb) adds two beta -rings. Here we describe a cDNA encoding LCYe in romaine lettuce (Lactuca sativa var. romaine), one of the few plant species known to accumulate substantial quantities of a carotenoid with two epsilon -rings: lactucaxanthin. The product of the lettuce cDNA, similar in sequence to the Arabidopsis LCYe (77% amino acid identity), efficiently converted lycopene into the bicyclic epsilon -carotene in a heterologous Escherichia coli system. Regions of the lettuce and Arabidopsis epsilon -cyclases involved in the determination of ring number were mapped by analysis of chimeric epsilon -cyclases constructed by using an inverse PCR approach. A single amino acid was found to act as a molecular switch: lettuce LCYe mutant H457L added only one epsilon -ring to lycopene, whereas the complementary Arabidopsis LCYe mutant, L448H, added two epsilon -rings. An R residue in this position also yields a bi-epsilon -cyclase for both the lettuce and Arabidopsis enzymes. Construction and analysis of chimera of related enzymes with differing catalytic activities provide an informative approach that may be of particular utility for studying membrane-associated enzymes that cannot easily be crystallized or modeled to existing crystal structures.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据