Molecular Cloning and Functional Characterization of a Novel Isoflavone 3'-O-methyltransferase from Pueraria lobata.

Pueraria lobata roots accumulate 3′-, 4′- and 7-O-methylated isoflavones and many of these methylated compounds exhibit various pharmacological activities. Either the 4′- or 7-O-methylation activity has been investigated at molecular levels in several legume species. However, the gene encoding the isoflavone 3′-O-methyltransferase (OMT) has not yet been isolated from any plant species. In this study, we reported the first cDNA encoding the isoflavone 3′-OMT from P. lobata (designated PlOMT4). Heterologous expressions in yeast and Escherichia coli cells showed that the gene product exhibits an enzyme activity to methylate the 3′-hydroxy group of the isoflavone substrate. The transcript abundance of PlOMT4 matches well with its enzymatic product in different organs of P. lobata and in the plant roots in response to methyl jasmonate elicitation. Integration of the biochemical with metabolic and transcript data supported the proposed function of PlOMT4. The identification of PlOMT4 would not only help to understand the isoflavonoid metabolism in P. lobata but also potentially provide an enzyme catalyst for methylating existing drug candidates to improve their hydrophobicity.

葛根积累3′ -、4′ -和7 - O -甲基化异黄酮，其中许多甲基化化合物表现出多种药理活性。在几种豆科植物中，4′ -或7 - O -甲基化活性已在分子水平上进行了研究。然而，编码异黄酮3′ - O -甲基转移酶（OMT）的基因尚未从任何植物物种中分离出来。在本研究中，我们报道了首个来自葛根的编码异黄酮3′ - OMT的cDNA（命名为PlOMT4）。在酵母和大肠杆菌细胞中的异源表达表明，该基因产物具有对异黄酮底物的3′ -羟基进行甲基化的酶活性。PlOMT4的转录本丰度与其在葛根不同器官以及茉莉酸甲酯诱导下的植物根中的酶产物高度吻合。生化数据与代谢和转录数据的整合支持了PlOMT4的假定功能。PlOMT4的鉴定不仅有助于理解葛根中的异黄酮代谢，还可能为甲基化现有候选药物以提高其疏水性提供一种酶催化剂。