人参皂苷生物合成和次生代谢工程

人参皂苷属于植物三萜皂苷类化合物,是传统名贵药材人参和西洋参的主要活性成分,具有抗炎、抗氧化作用,还有广泛的抗肿瘤作用。人参皂苷与植物甾醇共享前期代谢途径,通过2, 3-氧化鲨烯环化步骤进入三萜代谢分支途径,在三萜碳环骨架复杂修饰的基础上形成人参皂苷。综述了近年人参皂苷生物合成途径及关键酶基因研究的最新进展,揭示了人参皂苷生物合成的基本途径,对途径中关键酶的基因进行了综述,并结合次生代谢工程技术, 探讨了该技术在人参皂苷生物合成中的应用前景。     

植物三萜皂苷生物合成途径及调控机制研究进展

三萜皂苷是一类天然存在的结构多样的三萜苷类化合物,广泛分布于植物中.三萜皂苷不仅是植物抵御病原微生物和食草动物的防御化合物,还具有多种药理活性,被广泛应用在医药、日化、食品、农业等领域.近年来,随着科学技术的发展和研究的深入,植物三萜皂苷生物合成途径的基本框架及调控机制研究已经取得了一定的进展.植物三萜皂苷种类繁多、结构复杂,虽然有着共同的前体合成途径,但后修饰阶段具有高度特异性和多样性.本文综述了三萜皂苷的生物合成途径、关键酶基因、转录调控以及微生物细胞工程方面的研究进展,并对今后的发展方向进行了展望,以期为相关领域的研究提供参考.     

三叶木通转录组分析及三萜皂苷生物合成途径关键酶基因的发掘

为了解三叶木通(Akebia trifoliata(Thunb.)Koidz.)的三萜皂苷合成途径及其关键酶,本研究对其花、叶、根、茎进行转录组测序,组装获得了57.25 Gb数据,含140 859个unigenes,序列平均长度为1350 bp。KEGG代谢通路富集结果显示,517个unigenes参与三萜皂苷合成相关的3条代谢途径,其中415个unigenes编码三萜皂苷生物合成途径的19个关键酶。对三萜皂苷生物合成过程中的关键酶角鲨烯环氧酶(SE)进行序列分析和同源建模,发现其具有保守的底物结合结构域。将三叶木通茎与花、叶、根的基因表达水平进行比较,发现茎与根相比较其上调基因数目最多,其中295个差异表达基因(DEGs)与三萜皂苷生物合成途径相关。     

植物萜类生物合成中的后修饰酶

萜类化合物由于其结构类型丰富多样而被称为"terpenome".除了参与植物生长发育、环境应答等生理过程,萜类化合物还应用于医药、有机化工等领域.萜类的生物合成大致可分为前体形成、骨架构建以及后修饰三部分,基本骨架通常由萜类合酶催化形成,进一步在后修饰酶的作用下产生数以万计的萜类化合物.结合我们对香茶菜二萜生物合成的初步研究结果,本文主要针对近年来植物萜类生物合成中的一些有代表性的后修饰酶包括P450单氧酶、双键还原酶、酰基转移酶和糖基转移酶,进行研究现状分析与展望.     

三萜皂苷生物合成相关糖基转移酶研究进展

三萜皂苷具有独特的化学性质和丰富的药理活性,在医药、保健品、化妆品、食品添加剂、农业等方面被广泛应用.尿苷二磷酸(UDP)依赖的糖基转移酶(UGTs)是催化三萜皂苷生成的关键酶,对三萜皂苷的结构及其药理活性多样性的形成有重要作用.文中基于UGTs来源及受体底物结构类型对参与植物三萜皂苷生物合成的UGTs进行了综述,并展...     

三七总皂苷生物合成与关键酶调控的研究进展

三七总皂苷(PNS)属于达玛烷型三萜皂苷,是中国传统珍贵药材三七的主要活性成分,三七总皂苷在中枢神经系统、心脑血管系统、血液系统、免疫系统以及抗纤维化、抗衰老、抗肿瘤等方面均具有较好的生理活性.三七总皂苷是以达玛烯二醇为前体,在P450单加氧酶和糖基转移酶催化下形成.另外,三七总皂苷与植物甾醇共享前期代谢途径.该文对近年来国内外有关三七总皂苷的生物合成途径及关键酶基因的最新研究进展进行综述,并探讨了代谢工程在三七总皂苷生物合成中的应用前景.     

甾体皂甙的生物合成

近年来,人们分离鉴定了许多结构新颖的皂甙,阐明了它们的结构及生物活性,并对甾体皂甙的生物合成途径进行了较为深入的研究。异戊烯二磷酸在香叶二磷酸合成酶、法呢二磷酸合成酶、鲨烯合成酶和鲨烯环氧酶催化下合成2,3-环氧化鲨烯,再经环氧化鲨烯环化酶催化下形成三萜进而转化成甾醇,甾醇经羟化酶、糖基转移酶和β-糖苷酶的修饰,形成各种类型的甾体皂甙。本文重点介绍了甾体皂甙生物合成中所需要的关键酶,特别是以往研究较少的糖酶,主要为3-O-糖基转移酶,26-O-β-糖苷酶,并对甾体皂甙生物合成的前景进行了展望。     

三萜皂苷生物合成途径研究进展

三萜皂苷是一类重要的植物次生代谢产物,在体外具有抗癌、抗病毒、降低胆固醇等药理学作用。由于三萜皂苷生物合成途径中的关键酶在细胞中的表达水平较低,决定了其在植物中的含量低,因而对其生物合成途径的探讨具有重要的现实意义和应用价值。     

羽叶三七的转录组测序与三萜皂苷生物合成的关键酶基因的识别

羽叶三七是五加科人参属的名贵药材,三萜皂苷为羽叶三七最主要的活性成分。为了探索羽叶三七根茎中皂苷物质生物合成的分子基础,采用Illumina Hi Seq 2000高通量测序获得羽叶三七根茎的转录组数据;使用Trinity和TGICL软件实现Uni Gene的de novo拼接;基于BLAST完成Uni Gene的蛋白功能注释、KOG功能注释、GO分类和KEGG代谢通路分析。最终通过de novo拼接注释得到Uni Gene 62 240个。研究发现,羽叶三七根茎部表达的26个Uni Gene与三萜碳环骨架合成相关;三萜合成通路中的关键酶FPS、SS、SE等,分别有11 114个Uni Gene。该研究发现的三萜皂苷合成相关候选基因对于阐明羽叶三七三萜皂苷合成方式研究提供了理论基础。     

以生物合成为基础的红霉素A的产量提高和结构改造

红霉素A是一种广谱大环内酯类抗生素,在临床上应用广泛。其生物合成包括由聚酮合酶催化的十四元环骨架形成,以及羟基化、糖基化、甲基化后修饰。基于对红霉素A生物合成机制的认识,可以对产生菌种进行定向的遗传操作,达到产量提高和结构改造等目的。本文综述了近年来在红霉素A高产菌株改造和化学结构衍生方面所取得的研究进展,为相关研究人员提供参考。     

Saponins in cereals

Saponins are a diverse family of secondary metabolites that are produced by many plant species, particularly dicots. These molecules commonly have potent antifungal activity and their natural role in plants is likely to be in protection against attack by pathogenic microbes. They also have a variety of commercial applications including use as drugs and medicines. The enzymes, genes and biochemical pathways involved in the synthesis of these complex molecules are largely uncharacterized for any plant species. Cereals and grasses appear to be generally deficient in saponins with the exception of oats, which produce both steroidal and triterpenoid saponins. The isolation of genes for saponin biosynthesis from oats is now providing tools for the analysis of the evolution and regulation of saponin biosynthesis in monocots. These genes may also have potential for the development of improved disease resistance in cultivated cereals.     

Molecular activities, biosynthesis and evolution of triterpenoid saponins

Saponins are bioactive compounds generally considered to be produced by plants to counteract pathogens and herbivores. Besides their role in plant defense, saponins are of growing interest for drug research as they are active constituents of several folk medicines and provide valuable pharmacological properties. Accordingly, much effort has been put into unraveling the modes of action of saponins, as well as in exploration of their potential for industrial processes and pharmacology. However, the exploitation of saponins for bioengineering crop plants with improved resistances against pests as well as circumvention of laborious and uneconomical extraction procedures for industrial production from plants is hampered by the lack of knowledge and availability of genes in saponin biosynthesis. Although the ability to produce saponins is rather widespread among plants, a complete synthetic pathway has not been elucidated in any single species. Current conceptions consider saponins to be derived from intermediates of the phytosterol pathway, and predominantly enzymes belonging to the multigene families of oxidosqualene cyclases (OSCs), cytochromes P450 (P450s) and family 1 UDP-glycosyltransferases (UGTs) are thought to be involved in their biosynthesis. Formation of unique structural features involves additional biosynthetical enzymes of diverse phylogenetic background. As an example of this, a serine carboxypeptidase-like acyltransferase (SCPL) was recently found to be involved in synthesis of triterpenoid saponins in oats. However, the total number of identified genes in saponin biosynthesis remains low as the complexity and diversity of these multigene families impede gene discovery based on sequence analysis and phylogeny.This review summarizes current knowledge of triterpenoid saponin biosynthesis in plants, molecular activities, evolutionary aspects and perspectives for further gene discovery.     

Saponins and Phylogeny: Example of the “Gypsogenin group” Saponins

The chemical structure of triterpenoid saponins is quite complicated, especially the glucuronide oleanane-type triterpene carboxylic acid 3,28-bidesmosides (GOTCAB) saponins. Moreover, triterpenoid saponins are numerous as a result of this complicated structure. This review tries to explain this diversity in terms of plant classification and phylogeny. The study focuses on the three main successive steps of the biosynthetic pathway of the triterpenoid saponins: cyclisation, oxidation and glycosylation showing the relationship between triterpenols and sterols in terms of cell membrane evolution and the importance of which metabolic intermediates involved as aglycones of the triterpenoid saponins, represented progressively less and less in the advanced groups of the plant kingdom as they are more and more oxidised. This oxidation seems to reflect a better adaptation to new environmental conditions of some of these groups. By their enormous chemical diversity, the triterpenoid saponins seem to be good candidates to study the phylogeny of the flowering plants. A first attempt is given using recent advances in botanical classification for the orders and families by the Angiosperm Phylogenic Group (APG). This study was simplified in the first step focusing only on the “gypsogenin group” of the GOTCAB saponins. For example, as a result, these compounds are mainly concentrated in advanced groups such as Caryophyllideae, primitive Rosideae and Asterideae.