Patrick Owen S, Younkin Gordon C, Brody Rebecca G, Hem Jessica W, Jander Georg, Holland Cynthia K
Department of Biology, Williams College, Williamstown, Massachusetts, USA.
Plant Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, New York, USA; Boyce Thompson Institute, Ithaca, New York, USA.
J Biol Chem. 2025 Apr 30;301(6):108565. doi: 10.1016/j.jbc.2025.108565.
Cardenolides are potent plant-defensive metabolites that have been studied for decades for their significance in plant-insect interactions and their use in treating heart failure in humans. With recent advancements in genome and transcriptome sequencing, genes in the cardenolide biosynthetic pathway have begun to be identified. Here we employed gene co-expression network analysis using published data from the cardenolide-producing plant Erysimum cheiranthoides (wormseed wallflower) to identify two UDP-dependent glycosyltransferases, UGT73C44 and UGT73C45, that are capable of glucosylating the aglycone cardenolide digitoxigenin as well as other predicted cardenolide pathway intermediates. In vitro and in planta assays revealed that UGT73C44 acted on cardenolide pathway intermediates with a low K value of 7.0 μM for digitoxigenin, while UGT73C45 displayed broader substrate specificity in vitro and could glucosylate diverse steroid and flavonoid substrates. Phylogeny and comparisons of structural models of UGT73C44 and UGT73C45 suggest that the enzymes have divergent active site architectures, which may account for their different substrate specificities. These data report the first plant-derived UGT specific to cardenolides, advancing our understanding of cardenolide biosynthesis and the enzymes that drive specialized metabolite diversity. These findings lay the foundation for future efforts to reconstitute the cardenolide pathway in heterologous systems and design cardenolide analogs with the potential for improved therapeutic properties.
强心苷是强效的植物防御性代谢产物，数十年来，人们一直在研究它们在植物与昆虫相互作用中的重要性以及在治疗人类心力衰竭方面的用途。随着基因组和转录组测序技术的最新进展，强心苷生物合成途径中的基因已开始被鉴定出来。在这里，我们利用已发表的来自产生强心苷的植物桂竹香（糖芥）的数据进行基因共表达网络分析，以鉴定两种UDP依赖性糖基转移酶UGT73C44和UGT73C45，它们能够将强心苷苷元洋地黄毒苷以及其他预测的强心苷途径中间体进行糖基化。体外和体内实验表明，UGT73C44作用于强心苷途径中间体，对洋地黄毒苷的K值较低，为7.0 μM，而UGT73C45在体外表现出更广泛的底物特异性，并且能够将多种类固醇和类黄酮底物进行糖基化。UGT73C44和UGT73C45的系统发育和结构模型比较表明，这些酶具有不同的活性位点结构，这可能解释了它们不同的底物特异性。这些数据报道了首个植物来源的特异性作用于强心苷的UGT，增进了我们对强心苷生物合成以及驱动特殊代谢物多样性的酶的理解。这些发现为未来在异源系统中重建强心苷途径以及设计具有改善治疗特性潜力的强心苷类似物奠定了基础。
