Daurichromenic acid (DCA) synthase catalyzes the oxidative cyclization of grifolic acid to produce DCA, an anti-HIV meroterpenoid isolated from Rhododendron dauricum We identified a novel cDNA encoding DCA synthase by transcriptome-based screening from young leaves of R. dauricum The gene coded for a 533-amino acid polypeptide with moderate homologies to flavin adenine dinucleotide oxidases from other plants. The primary structure contained an amino-terminal signal peptide and conserved amino acid residues to form bicovalent linkage to the flavin adenine dinucleotide isoalloxazine ring at histidine-112 and cysteine-175. In addition, the recombinant DCA synthase, purified from the culture supernatant of transgenic Pichia pastoris, exhibited structural and functional properties as a flavoprotein. The reaction mechanism of DCA synthase characterized herein partly shares a similarity with those of cannabinoid synthases from Cannabis sativa, whereas DCA synthase catalyzes a novel cyclization reaction of the farnesyl moiety of a meroterpenoid natural product of plant origin. Moreover, in this study, we present evidence that DCA is biosynthesized and accumulated specifically in the glandular scales, on the surface of R. dauricum plants, based on various analytical studies at the chemical, biochemical, and molecular levels. The extracellular localization of DCA also was confirmed by a confocal microscopic analysis of its autofluorescence. These data highlight the unique feature of DCA: the final step of biosynthesis is completed in apoplastic space, and it is highly accumulated outside the scale cells.

中文翻译：

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鉴定和表征抗艾滋病毒生物合成中的柔红霉素酸合酶。

柔红霉素（DCA）合酶催化谷氨酸的氧化环化反应以产生DCA，这是一种从杜鹃杜鹃中分离出来的抗HIV甲萜类化合物。我们通过基于转录组的筛选，从红杜鹃幼叶中鉴定了编码DCA合酶的新cDNA。一种与其他植物的黄素腺嘌呤二核苷酸氧化酶具有中等同源性的533个氨基酸的多肽。一级结构包含一个氨基末端信号肽和保守的氨基酸残基，以在组氨酸-112和半胱氨酸-175处与黄素腺嘌呤二核苷酸异恶嗪环形成双价连接。另外，从转基因巴斯德毕赤酵母的培养上清液中纯化的重组DCA合酶表现出作为黄素蛋白的结构和功能特性。本文表征的DCA合酶的反应机理与来自大麻的大麻素合酶的部分相似，而DCA合酶催化植物来源的类萜类天然产物的法呢基部分的新型环化反应。此外，在这项研究中，我们基于化学，生物化学和分子水平的各种分析研究，提供了DCA是生物合成的且特别累积在红唇植物表面的腺体鳞片的证据。DCA的细胞外定位也通过其自发荧光的共聚焦显微镜分析得到了证实。这些数据突出了DCA的独特功能：生物合成的最后一步在质外体空间中完成，并且在鳞片细胞外高度积累。