GUX1 and GUX2 glucuronyltransferases decorate distinct domains of glucuronoxylan with different substitution patterns
GUX1 and GUX2 glucuronyltransferases decorate distinct domains of glucuronoxylan with different substitution patterns
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DOI：
10.1111/tpj.12135
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发表时间：
2013-05-01
期刊：
影响因子：
7.2
通讯作者：
Dupree, Paul
中科院分区：
文献类型：
--
作者：
Bromley, Jennifer R.;Busse-Wicher, Marta;Dupree, Paul
木聚糖占植物细胞壁的三分之一，它影响生物质的性质和加工。拟南芥中葡糖醛酸木聚糖的特征是由葡萄糖醛酸和4-O-甲基葡萄糖醛酸(统称为[Me]Glca)取代的木糖基(1，4)连接的骨架。这些替换的作用尚不清楚。GUX1(葡糖醛酸取代木聚糖1)和GUX2是最近发现的葡萄糖糖醛酸基转移酶，它们都是用[Me]Glca取代木聚糖骨架所必需的。在这里，我们展示了由每种葡萄糖醛酸基转移酶产生的[Me]GLCA取代模式的明显差异。GUX1修饰木聚糖时，倾向于在均匀分布的木糖基残基上添加[Me]Glca。8个或10个残基的间隔占主导地位，但观察到较大的间隔。相比之下，GUX2产生的装饰更紧密地聚集在一起，最频繁的间距是5个、6个或7个木糖基残基，不偏爱奇数或偶数间距。此外，这些GUX转移酶中的每一个都取代了次生细胞壁木聚糖的一个不同的结构域，我们称之为主要结构域和次要结构域。这些主要和次要的木聚糖结构域不能通过大小或电荷彼此分开，这一发现表明它们是紧密相关的。这两个不同的[Me]Glca修饰结构域的存在可能会产生性质不同的木聚糖分子。我们推测木聚糖的主要结构域和次要结构域可能是专门化的，例如与纤维素或木质素的相互作用。这些发现对我们理解木聚糖的合成和结构，以及植物细胞壁的木质纤维基质的分子结构模型具有重要的意义。
Xylan comprises up to one-third of plant cell walls, and it influences the properties and processing of biomass. Glucuronoxylan in Arabidopsis is characterized by a linear -(1,4)-linked backbone of xylosyl residues substituted by glucuronic acid and 4-O-methylglucuronic acid (collectively termed [Me]GlcA). The role of these substitutions remains unclear. GUX1 (glucuronic acid substitution of xylan 1) and GUX2, recently identified as glucuronyltransferases, are both required for substitution of the xylan backbone with [Me]GlcA. Here, we demonstrate clear differences in the pattern of [Me]GlcA substitution generated by each of these glucuronyltransferases. GUX1 decorates xylan with a preference for addition of [Me]GlcA at evenly spaced xylosyl residues. Intervals of eight or 10 residues dominate, but larger intervals are observed. GUX2, in contrast, produces more tightly clustered decorations with most frequent spacing of five, six or seven xylosyl residues, with no preference for odd or even spacing. Moreover, each of these GUX transferases substitutes a distinct domain of secondary cell wall xylan, which we call the major and minor domains. These major and minor xylan domains were not separable from each other by size or charge, a finding that suggests that they are tightly associated. The presence of both differently [Me]GlcA decorated domains may produce a xylan molecule that is heterogeneous in its properties. We speculate that the major and minor domains of xylan may be specialised, such as for interaction with cellulose or lignin. These findings have substantial implications for our understanding of xylan synthesis and structure, and for models of the molecular architecture of the lignocellulosic matrix of plant cell walls.