Lignins: Natural polymers from oxidative coupling of 4-hydroxyphenylpropanoids
Lignins: Natural polymers from oxidative coupling of 4-hydroxyphenylpropanoids
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DOI：
10.1023/b:phyt.0000047809.65444.a4
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发表时间：
2004-01-01
影响因子：
7.7
通讯作者：
Boerjan, Wout
中科院分区：
文献类型：
--
作者：
Ralph, John;Lundquist, Knut;Boerjan, Wout
木质素是复杂的天然聚合物，主要由4-羟基苯丙素类氧化偶联产生。由于详细的结构研究，对它们的性质的理解正在发展，最近由于木质素生物合成途径突变体和转基因的可用性而有所帮助。目前公认的理论是，木质素聚合物是在简单的化学控制下，经由过氧化物酶-H2 O2产生的自由基，通过类似组合的酚偶联反应形成的，其中单木质素与生长的聚合物末端反应。因此，木质素大分子的实际结构并没有绝对定义或确定。连接生成的“随机性”（这不是真正的统计随机性，而是受反应物供应、基质等的控制，就像任何化学反应一样）。和天文数字的可能的异构体，甚至一个简单的聚合物结构，表明两个木质素大分子是相同的可能性很低。最近对目前公认的化学控制木质化理论的挑战，试图使木质素与更有组织的生物聚合物如蛋白质保持一致，这在逻辑上与木质素结构的最基本细节不一致。木质素可以部分地衍生自除了三种主要单木质素醇（对香豆醇、松柏醇和芥子醇）之外的单体和缀合物。组合聚合反应的可塑性允许单体取代和最终结构的显著变化，在许多情况下，植物似乎可以耐受。因此，木质化被看作是一种恶性进化的过程，允许植物在处理各种环境胁迫方面具有相当大的灵活性，并赋予它们即使在人类或自然改变“所需”木质素生物合成途径基因/酶时仍能保持活力的惊人能力。缩写：4CL - 4-香豆酸：CoA连接酶; C3 H-对香豆酸3-羟化酶; HCT -对羟基肉桂酰-CoA：奎尼酸什基马替对羟基肉桂酰转移酶; CCoAOMT -咖啡酰-CoAO-甲基转移酶; CCR -肉桂酰-CoA还原酶; F5 H-阿魏酸5-羟化酶; CAld 5 H-松柏醛5-羟化酶; COMT -咖啡酸O-甲基转移酶; AldOMT -（5-羟基针叶树）脱氢O-甲基转移酶; CAD -肉桂醇脱氢酶; NMR -核磁共振（光谱学）; DFRC -衍生化，随后还原裂解; TIZ -甲苯磺酰化、碘化、锌（DFRC方法）; DHP -脱氢聚合物。
Lignins are complex natural polymers resulting from oxidative coupling of, primarily, 4-hydroxyphenylpropanoids. An understanding of their nature is evolving as a result of detailed structural studies, recently aided by the availability of lignin-biosynthetic-pathway mutants and transgenics. The currently accepted theory is that the lignin polymer is formed by combinatorial-like phenolic coupling reactions, via radicals generated by peroxidase-H2O2, under simple chemical control where monolignols react endwise with the growing polymer. As a result, the actual structure of the lignin macromolecule is not absolutely defined or determined. The ``randomness'' of linkage generation (which is not truly statistically random but governed, as is any chemical reaction, by the supply of reactants, the matrix, etc.) and the astronomical number of possible isomers of even a simple polymer structure, suggest a low probability of two lignin macromolecules being identical. A recent challenge to the currently accepted theory of chemically controlled lignification, attempting to bring lignin into line with more organized biopolymers such as proteins, is logically inconsistent with the most basic details of lignin structure. Lignins may derive in part from monomers and conjugates other than the three primary monolignols (p-coumaryl, coniferyl, and sinapyl alcohols). The plasticity of the combinatorial polymerization reactions allows monomer substitution and significant variations in final structure which, in many cases, the plant appears to tolerate. As such, lignification is seen as a marvelously evolved process allowing plants considerable flexibility in dealing with various environmental stresses, and conferring on them a striking ability to remain viable even when humans or nature alter ``required'' lignin-biosynthetic-pathway genes/enzymes. The malleability offers significant opportunities to engineer the structures of lignins beyond the limits explored to date.Abbreviations:4CL – 4-coumarate:CoA ligase; C3H –p-coumarate 3-hydroxylase; HCT –p-hydroxycinnamoyl-CoA: quinate shikimatep-hydroxycinnamoyltransferase; CCoAOMT – caffeoyl-CoAO-methyltransferase; CCR – cinnamoyl-CoA reductase; F5H – ferulate 5-hydroxylase; CAld5H – coniferaldehyde 5-hydroxylase; COMT – caffeic acidO-methyltransferase; AldOMT – (5-hydroxyconifer)aldehydeO-methyltransferase; CAD – cinnamyl alcohol dehydrogenase; NMR – nuclear magnetic resonance (spectroscopy); DFRC – derivatization followed by reductive cleavage; TIZ – tosylation, iodination, zinc (a DFRC method); DHP – dehydrogenation polymer.