Characterization of two candidate flavone 8-O-methyltransferases suggests the existence of two potential routes to nevadensin in sweet basil
Characterization of two candidate flavone 8-O-methyltransferases suggests the existence of two potential routes to nevadensin in sweet basil
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DOI：
10.1016/j.phytochem.2013.05.001
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发表时间：
2013-08-01
期刊：
影响因子：
3.8
通讯作者：
Gang, David R.
中科院分区：
文献类型：
--
作者：
Berim, Anna;Gang, David R.
区域选择性6-、7-、8-、3 '-和4'-O-甲基化是甜罗勒毛状体中产生的亲脂性黄酮结构多样性的基础。位置6、7和4'被最近描述的一组阳离子非依赖性酶甲基化。阳离子依赖的O-甲基转移酶的作用仍然需要阐明。在这里，罗勒毛EST数据库被用来确定一个Me依赖的O-甲基转移酶，很可能接受类黄酮作为底物。重组蛋白被发现与广泛的O-二酚是活性的，并甲基化的黄酮骨架的8-OH部分具有更高的催化效率比3 '-OH基团的候选底物。为了进一步研究黄酮8-O-甲基化，用可用的底物类似物评估来自相同EST集合的推定的阳离子非依赖性黄酮8-O-甲基转移酶的活性。值得注意的是，它被其预期产物之一栀子苷B强烈抑制。这两种蛋白质的催化能力表明，可能存在两种替代途径，以nevadensin，在一些罗勒品种的主要黄酮。相关的表达的基础基因的积累8-取代的黄酮在四个罗勒线没有澄清，这是主要的操作途径在体内，但结合数据表明，黄酮7-O-脱甲基酶的生化特性可以发挥关键作用，在确定反应顺序。(C)2013爱思唯尔有限公司保留所有权利。
Regioselective 6-,7-,8-,3'-, and 4'-O-methylations underlie the structural diversity of lipophilic flavones produced in the trichomes of sweet basil (Ocimum basilicum L.). The positions 6, 7, and 4' are methylated by a recently described set of cation-independent enzymes. The roles of cation-dependent O-methyltransferases still require elucidation. Here, the basil trichome EST database was used to identify a Me-dependent O-methyltransferase that was likely to accept flavonoids as substrates. The recombinant protein was found to be active with a wide range of O-diphenols, and methylated the 8-OH moiety of the flavone backbone with higher catalytic efficiency than the 3'-OH group of candidate substrates. To further investigate flavone 8-O-methylation, the activity of a putative cation-independent flavonoid 8-O-methyltransferase from the same EST collection was assessed with available substrate analogs. Notably, it was strongly inhibited by garderiin B, one of its expected products. The catalytic capacities of the two studied proteins suggest that two alternative routes to nevadensin, a major flavone in some basil cultivars, might exist. Correlating the expression of the underlying genes with the accumulation of 8-substituted flavones in four basil lines did not clarify which is the major operating pathway in vivo, yet the combined data suggested that the biochemical properties of flavone 7-O-demethylase could play a key role in determining the reaction order. (C) 2013 Elsevier Ltd. All rights reserved.