XAX1 from glycosyltransferase family 61 mediates xylosyltransfer to rice xylan
XAX1 from glycosyltransferase family 61 mediates xylosyltransfer to rice xylan
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DOI：
10.1073/pnas.1202079109
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发表时间：
2012-10-16
影响因子：
11.1
通讯作者：
Ronald, Pamela C.
中科院分区：
文献类型：
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作者：
Chiniquy, Dawn;Sharma, Vaishali;Ronald, Pamela C.
木聚糖是地球上第二丰富的多糖，代表着用于生物燃料生产的大量储存能量。尽管它的重要性，大多数合成木聚糖的酶还没有被确定。木聚糖具有β-1，4-连接的木糖残基的主链，其具有包括α-（1 -> 2）-连接的葡糖醛酸基、4-O-甲基葡糖醛酸基和α-1，2-和α-1，3-阿拉伯呋喃糖基残基的取代。这些取代在结构上是多样的，并且根据分类学而变化，其中草木聚糖代表不同于双子叶植物和其他单子叶植物的独特组成。迄今为止，尚未鉴定出对草木聚糖合成具有特异性的酶。我们在Os 02 g22380中鉴定了一个木糖缺陷的功能丧失型水稻突变体，Os 02 g22380是GT 61家族的草特异性亚家族中的一个推定的糖基转移酶。我们将木聚糖1的木糖阿拉伯糖基取代的突变体命名为xax 1。木聚糖的酶指纹图谱显示突变体中特定的峰缺失，该峰被分离并通过H-1-NMR确定为（β-1，4-Xyl）（4）和β-Xylp-（1 -> 2）-α-Araf-（1 -> 3）。水稻xax 1突变体植物缺乏阿魏酸和香豆酸，已知这些芳香族化合物与木聚糖中被木糖残基取代的阿拉伯糖残基相连。XAX 1突变体植物表现出增加的木聚糖的可提取性和增加的糖化，可能反映了较低程度的二阿魏酸交联。从瞬时表达XAX 1的烟草植物中分离的微粒体的活性测定证明了对内源性受体的木糖基转移酶活性。我们的研究结果提供了深入了解草木聚糖合成和如何取代可能被修改为增加糖化生物燃料的产生。
Xylan is the second most abundant polysaccharide on Earth and represents an immense quantity of stored energy for biofuel production. Despite its importance, most of the enzymes that synthesize xylan have yet to be identified. Xylans have a backbone of beta-1,4-linked xylose residues with substitutions that include alpha-(1 -> 2)-linked glucuronosyl, 4-O-methyl glucuronosyl, and alpha-1,2- and alpha-1,3-arabinofuranosyl residues. The substitutions are structurally diverse and vary by taxonomy, with grass xylan representing a unique composition distinct from dicots and other monocots. To date, no enzyme has yet been identified that is specific to grass xylan synthesis. We identified a xylose-deficient loss-of-function rice mutant in Os02g22380, a putative glycosyltransferase in a grass-specific subfamily of family GT61. We designate the mutant xax1 for xylosyl arabinosyl substitution of xylan 1. Enzymatic fingerprinting of xylan showed the specific absence in the mutant of a peak, which was isolated and determined by H-1-NMR to be (beta-1,4-Xyl)(4) with a beta-Xylp-(1 -> 2)-alpha-Araf-(1 -> 3). Rice xax1 mutant plants are deficient in ferulic and coumaric acid, aromatic compounds known to be attached to arabinosyl residues in xylan substituted with xylosyl residues. The xax1 mutant plants exhibit an increased extractability of xylan and increased saccharification, probably reflecting a lower degree of diferulic cross-links. Activity assays with microsomes isolated from tobacco plants transiently expressing XAX1 demonstrated xylosyltransferase activity onto endogenous acceptors. Our results provide insight into grass xylan synthesis and how substitutions may be modified for increased saccharification for biofuel generation.