Lignins, (Oligo)lignans, and

这个特殊的项目将作为第一个目标来确定是否在杜仲科、亚麻科、荆芥科和Larrea种中存在一整类直接蛋白，并且它们在规定的独特的8-8’耦合模式中单独存在差异。预计每种选定的植物物种都含有不同的直接蛋白，这些直接蛋白在所利用的首选底物和/或自由基-自由基偶联过程中产生的立体选择性上有所不同。通过cDNA文库筛选和/或RT-PCR方法，将获得每个物种的直接源蛋白同源物，并通过功能活性重组直接源蛋白的异源表达确定编码的特定偶联模式。此外，这一阶段的研究将包括在组织和（亚）细胞水平上确定这些特定物种中直接蛋白基因表达/蛋白质定位所涉及的组织和发育阶段。在本研究的第二个目标中，我们将试图证明植物细胞壁的木质素化是通过直接蛋白位点（或同等物）的参与来规定的，这些直接蛋白位点控制着链接类型和所涉及的单体。我们将特别关注在体外获得的木质素中所谓的8-O-4'键的形成，因为这种键在体内木质素中占主导地位。木质素生物聚合物和（低聚）木脂素占生物圈循环有机碳的近30%，是维管植物的主要成分。木质素是细胞壁结构成分，没有它，植物既不能直立，也不能形成木本组织；（低聚）木脂素虽然来源于与木质素相同的前体，但用于植物防御作用（例如，作为抗氧化剂，杀菌剂，抗病毒和拒食化合物等）。目前的项目建立在我们最近发现的直接蛋白的基础上，这反过来又为生物体（植物）控制自由基-自由基耦合结果的主要机制之一提供了深刻的见解。在这一发现之前，这种转化一直被认为只存在于非特异性氧化转化领域，例如由O2/漆酶和过氧化物酶/H2O2催化的转化。

Lewis This particular project will establish as the first objective whether an entire class of dirigent proteins exists in Eucommia, Linum, Schizandra and Larrea species, and which individually differ in the distinctive 8-8' coupling modes stipulated. It is anticipated that each selected plant species harbors a distinct dirigent protein which differs in either preferred substrate utilized and/or stereoselectivity engendered during radical-radical coupling. Using either cDNA library screening and/or RT-PCR approaches, the dirigent protein homologues from each species will be obtained, with specific coupling modes encoded determined through heterologous expression of functionally competent recombinant dirigent proteins. Additionally, this phase of the study will include identifying the tissues and developmental stages involved in dirigent protein gene expression/protein localization in these particular species, at tissue and (sub)cellular levels. In the second objective of this study, we will seek to demonstrate that lignification in the plant cell wall is stipulated through the participation of arrays of dirigent protein sites (or an equivalent thereof) which control both linkage type and monomer(s) involved. Particular attention will be given to demonstrating formation of the so-called 8-O-4' linkage in lignins obtained in vitro, since this linkage predominates in lignins in vivo. The lignin biopolymers and (oligomeric) lignans account for nearly 30% of organic carbon circulating in the biosphere, being major constituents of vascular plants. The lignins are structural cell wall constituents without which plants would be unable to either stand vertically and/or form their woody tissues; the (oligomeric) lignans, while derived from the same precursors as lignins, are employed in plant defense roles (e.g. as antioxidants, bactericides, antiviral and antifeedant compounds, etc.). The current project builds on our recent discovery of dirigent proteins which, in turn, gives incisive insight into at least one of the principal mechanisms whereby living organisms (plants) can control the outcome of radical-radical coupling. Until this discovery, such conversions had been considered as solely in the realm of non-specific oxidative conversions, such as those catalyzed by O2/laccases and peroxidases/H2O2.