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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Functional reclassification of the putative cinnamyl alcohol dehydrogenase multigene family in Arabidopsis
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Functional reclassification of the putative cinnamyl alcohol dehydrogenase multigene family in Arabidopsis

机译：拟南芥中肉桂醇脱氢酶多基因家族的功能重分类

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摘要

Of 17 genes annotated in the Arabidopsis genome database as cinnamyl alcohol dehydrogenase (CAD) homologues, an in silico analysis revealed that 8 genes were misannotated. Of the remaining nine, six were catalytically competent for NADPH-dependent reduction of p-coumaryl, caffeyl, coniferyl, 5-hydroxyconiferyl, and sinapyl aldehydes, whereas three displayed very low activity and only at very high substrate concentrations. Of the nine putative CADs, two (AtCAD5 and AtCAD4) had the highest activity and homology (≈83% similarity) relative to bona fide CADs from other species. AtCAD5 used all five substrates effectively, whereas AtCAD4 (of lower overall catalytic capacity) poorly used sinapyl aldehyde; the corresponding 270-fold decrease in k_(enz) resulted from higher K_m and lower k_(cat) values, respectively. No CAD homologue displayed a specific requirement for sinapyl aldehyde, which was in direct contrast with unfounded claims for a so-called sinapyl alcohol dehydrogenase in angiosperms. AtCAD2, 3, as well as AtCAD7 and 8 (highest homology to sinapyl alcohol dehydrogenase) were catalytically less active overall by at least an order of magnitude, due to increased K_m and lower k_(cat) values. Accordingly, alternative and/or bifunctional metabolic roles of these proteins in plant defense cannot be ruled out. Comprehensive analyses of lignified tissues of various Arabidopsis knockout mutants (for AtCAD5, 6, and 9) at different stages of growth/development indicated the presence of functionally redundant CAD metabolic networks. Moreover, disruption of AtCAD5 expression had only a small effect on either overall lignin amounts deposited, or on syringyl-guaiacyl compositions, despite being the most catalytically active form in vitro.
机译：在拟南芥基因组数据库中标注为肉桂醇脱氢酶（CAD）同源物的17个基因中，计算机分析表明有8个基因被错误标注。在其余的9个中，有6个具有催化能力，可对NADPH依赖性还原对香豆醛，咖啡酰基，松柏基，5-羟基松柏基和芥子醛，而三个则表现出非常低的活性，并且仅在很高的底物浓度下显示。在9个推定的CAD中，有两个（AtCAD5和AtCAD4）相对于其他物种的真正CAD具有最高的活性和同源性（约83％相似性）。 AtCAD5有效地使用了所有五种底物，而AtCAD4（总体催化能力较低）则很少使用芥子醛。 k_（enz）相应降低了270倍，分别是由较高的K_m和较低的k_（cat）值引起的。没有CAD同源物显示出对芥子醛的特殊要求，这与被子植物中所谓的芥子醇脱氢酶的毫无根据的主张直接相反。由于增加的K_m和较低的k_（cat）值，AtCAD2、3以及AtCAD7和8（与芥子醇脱氢酶的同源性最高）总体上具有较低的催化活性。因此，不能排除这些蛋白质在植物防御中的替代和/或双功能代谢作用。在生长/发育的不同阶段对各种拟南芥基因敲除突变体（对于AtCAD5、6和9）的木质化组织进行全面分析，表明存在功能上多余的CAD代谢网络。而且，尽管AtCAD5表达的破坏是体外最具催化活性的形式，但它对沉积的木质素总量或丁香基-愈创木基组合物的影响很小。

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