Proanthocyanidin Biosynthesis in Plants PURIFICATION OF LEGUME LEUCOANTHOCYANIDIN REDUCTASE AND MOLECULAR CLONING OF ITS cDNA*□S
Proanthocyanidin Biosynthesis in Plants PURIFICATION OF LEGUME LEUCOANTHOCYANIDIN REDUCTASE AND MOLECULAR CLONING OF ITS cDNA*□S
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发表时间：
2003
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通讯作者：
G. Tanner;K. Francki;S. Abrahams;J. Watson;P. Larkin;A. R. Ashton
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作者：
G. Tanner;K. Francki;S. Abrahams;J. Watson;P. Larkin;A. R. Ashton
无色花青素还原酶（LAR）催化3，4-顺式无色花青素合成缩合单宁或原花青素（PA）的起始单体儿茶素，是PA生物合成的第一个关键步骤。从豆科植物山蚂蝗Desmodium uncinatum（Jacq.）DC，部分测序并克隆相应的cDNA。通过在大肠杆菌中以及在烟草和白色三叶草中表达活性重组LAR来确认酶的身份。该酶是43 kDa（382个氨基酸）的单体，并且是合成儿茶素最活跃的（比活性为10 mol/min 1 mg蛋白质），但也合成afzelechin和没食子儿茶素。LAR与作为还原酶-差向异构酶-脱氢酶（RED）蛋白质家族的一部分的植物酶的α-还原酶组最密切相关。与所有其他植物的β-还原酶同源物（约320个氨基酸长）不同，LAR具有额外的65个氨基酸的C-末端延伸，其功能尚不清楚。奇怪的是，虽然拟南芥制造PA，但在拟南芥基因组中没有明显的LAR直系同源物。这可能是因为拟南芥似乎只产生表儿茶素，而不是类似于许多其他植物的基于儿茶素/表儿茶素的双重PA。
Leucoanthocyanidin reductase (LAR) catalyzes the synthesis of catechin, an initiating monomer of condensed tannin or proanthocyanidin (PA) synthesis, from 3,4-cis-leucocyanidin and thus is the first committed step in PA biosynthesis. The enzyme was purified to near homogeneity from PA-rich leaves of the legume Desmodium uncinatum (Jacq.) DC, partially sequenced and the corresponding cDNA cloned. The identity of the enzyme was confirmed by expressing active recombinant LAR in Escherichia coli and in tobacco and white clover. The enzyme is a monomer of 43 kDa (382 amino acids) and is most active synthesizing catechin (specific activity of 10 mol min 1 mg of protein ) but also synthesizes afzelechin and gallocatechin. LAR is most closely related to the isoflavone reductase group of plant enzymes that are part of the Reductase-Epimerase-Dehydrogenase (RED) family of proteins. Unlike all other plant isoflavone reductase homologues that are about 320 amino acids long, LAR has an additional 65amino acid C-terminal extension whose function is not known. Curiously, although Arabidopsis makes PA, there is no obvious LAR orthologue in the Arabidopsis genome. This may be because Arabidopsis seems to produce only an epicatechin, rather than a dual catechin/ epicatechin-based PA similar to many other plants.