An ancient enzyme domain hidden in the putative β-glucan elicitor receptor of soybean may play an active part in the perception of pathogen-associated molecular patterns during broad host resistance
An ancient enzyme domain hidden in the putative β-glucan elicitor receptor of soybean may play an active part in the perception of pathogen-associated molecular patterns during broad host resistance
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DOI：
10.1074/jbc.m308552200
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发表时间：
2004-01-09
影响因子：
4.8
通讯作者：
Ebel, J
中科院分区：
文献类型：
--
作者：
Fliegmann, J;Mithöfer, A;Ebel, J
对潜在病原体的成功防御要求宿主有机体能够区分自我和非自我结构。大豆（Glycine max L.）利用一种特殊的分子模式，一种1,6- β -连接和1,3- β -支链的七糖苷（HG），作为一种信号化合物，存在于子宫真菌病原体大豆疫霉菌（Phytophthora sojae）的细胞壁中，引发防御反应。特异性和高亲和力的hg结合位点包含在β -葡聚糖结合蛋白（GBP）中，而GBP又是拟议受体复合物的一部分。感知和响应疫霉菌细胞壁衍生的β -葡聚糖激发子的能力是豆科植物所独有的。然而，我们认为GBP的存在是必需的，但对于β -葡聚糖激发子依赖的抗病是不够的，因为编码GBP相关蛋白的基因可以从许多植物物种中检索到。此外，我们发现GBP由两个不同的碳水化合物活性蛋白结构域组成，一个包含β -葡聚糖结合位点，另一个与真菌来源的葡聚糖内切葡萄糖苷酶有关。葡聚糖水解酶最有可能表现出一种内特异性的作用模式，只切割由至少四个部分组成的低聚葡萄糖苷的1,3- β - d -糖苷键。因此，GBP固有的内-1,3- β -葡聚糖酶活性在与疫霉菌初次接触时完全适合释放富含基序的低聚葡萄糖苷片段，这些基序构成了同一蛋白质中高亲和力结合位点的配体。植物先天免疫的概念得到了这个高度复杂的系统的大力支持，该系统使用古老的酶模块作为识别机制的活跃部分。
A successful defense against potential pathogens requires that a host organism is able to discriminate between self and nonself structures. Soybean (Glycine max L.) exploits a specific molecular pattern, a 1,6-beta-linked and 1,3-beta-branched heptaglucoside (HG), present in cell walls of the oomycetal pathogen Phytophthora sojae, as a signal compound eliciting the onset of defense reactions. The specific and high affinity HG-binding site is contained in the beta-glucan-binding protein (GBP), which in turn is part of a proposed receptor complex. The ability to perceive and respond to Phytophthora cell wall-derived beta-glucan elicitors is exclusive to plants that belong to the Fabaceae. However, we propose that the presence of the GBP is essential, but not sufficient for beta-glucan elicitor-dependent disease resistance because genes encoding GBP-related proteins can be retrieved from many plant species. Furthermore, we show that the GBP is composed of two different carbohydrate-active protein domains, one containing the beta-glucan-binding site, and the other related to glucan endoglucosidases of fungal origin. The glucan hydrolase displays most likely an endo-specific mode of action, cleaving only 1,3-beta-D-glucosidic linkages of oligoglucosides consisting of at least four moieties. Thus, the intrinsic endo-1,3-beta-glucanase activity of the GBP is perfectly suited during initial contact with Phytophthora to release oligoglucoside fragments enriched in motifs that constitute ligands for the high affinity binding site present in the same protein. The concept of innate immunity in plants receives substantial support by this highly sophisticated system using ancient enzyme modules as an active part of the recognition mechanism.