Characterization of a caffeic acid 3-O-methyltransferase from wheat and its function in lignin biosynthesis
Characterization of a caffeic acid 3-O-methyltransferase from wheat and its function in lignin biosynthesis
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小麦咖啡酸 3-O-甲基转移酶的表征及其在木质素生物合成中的功能。
DOI：
10.1016/j.biochi.2007.09.016
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发表时间：
2008-03-01
期刊：
影响因子：
3.9
通讯作者：
Xu, Yang
中科院分区：
文献类型：
--
作者：
Ma, Qing-Hu;Xu, Yang
咖啡酸3-O-甲基转移酶(COMT)催化木质素单体羟基化前体的多步甲基化反应，在木质素生物合成途径中占有举足轻重的地位。从小麦中鉴定出一个cDNA(TaCM)，它在茎、叶和根组织中有成分表达。推导的TaCM氨基酸序列与其他植物的COMT有很高的同源性，特别是在SAM结合基序以及负责催化和底物专一性的残基上。预测的TaCM三维结构与来自紫花苜蓿的COMT(MsCOMT)非常相似，并且TaCM蛋白与MsCOMT抗体具有很高的免疫反应性。动力学分析表明，重组TaCM蛋白对咖啡醛和5-羟基针叶醛的催化效率最高，提示可能是通过醛前体生成S木质素的。反义TaCM基因在转基因烟草中的表达特异性地下调了COMT酶的活性，证实了编码COMT的TaCM基因的权威性。木质素分析表明，COMT活性的降低导致木质素含量略有下降，但针叶木质素含量急剧下降。此外，TaCM蛋白对咖啡酰辅酶A和5-羟基阿魏酰辅酶A等酯类前体具有很强的活性。我们的结果表明，TaCM是参与木质素生物合成的典型的COMT。它还支持与结构分析一致的观点，即COMT具有广泛的底物偏好。(C)2007年爱思唯尔·马森公司。版权所有。
Caffeic acid 3-O-methyltransferase (COMT) catalyzes the multi-step methylation reactions of hydroxylated monomeric lignin precursors, and is believed to occupy a pivotal position in the lignin biosynthetic pathway. A cDNA (TaCM) was identified from wheat and it was found to be expressed constitutively in stem, leaf and root tissues. The deduced amino acid sequence of TaCM showed a high degree of identity with COMT from other plants, particularly in SAM binding motif and the residues responsible for catalytic and substrate specificity. The predicted TaCM three-dimensional structure is very similar with a COMT from alfalfa (MsCOMT), and TaCM protein had high immunoreactive activity with MsCOMT antibody. Kinetic analysis indicated that the recombinant TaCM protein exhibited the highest catalyzing efficiency towards caffeoyl aldehyde and 5-hydroxyconiferaldehyde as substrates, suggesting a pathway leads to S lignin via aldehyde precursors. Authority of TaCM encoding a COMT was confirmed by the expression of antisense TaCM gene in transgenic tobacco which specifically down-regulated the COMT enzyme activity. Lignin analysis showed that the reduction in COMT activity resulted in a marginal decrease in lignin content but sharp reduction in the syringl lignin. Furthermore, the TaCM protein exhibited a strong activity towards ester precursors including caffeoyl-CoA and 5-hydroxyferuloyl-CoA. Our results demonstrate that TaCM is a typical COMT involved in lignin biosynthesis. It also supports the notion, in agreement with a structural analysis, that COMT has a broad substrate preference. (c) 2007 Elsevier Masson SAS. All rights reserved.