Boron bridging of rhamnogalacturonan-II is promoted in vitro by cationic chaperones, including polyhistidine and wall glycoproteins.
Boron bridging of rhamnogalacturonan-II is promoted in vitro by cationic chaperones, including polyhistidine and wall glycoproteins.
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DOI：
10.1111/nph.13596
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发表时间：
2016-01
期刊：
影响因子：
--
通讯作者：
Fry SC
中科院分区：
文献类型：
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作者：
Chormova D;Fry SC
鼠李糖半乳糖酸- II （RG - II）通过硼交联二聚化有助于细胞壁的组装和生物物理特性。纯RG‐II仅在添加非生物制剂（例如Pb2+）时才能在体外被硼酸（B(OH)3）有效地二聚。相比之下，新合成的RG‐II结构域在体内迅速二聚化。我们调查了可能导致这种情况的生物制剂。我们测试了三种这样的试剂：新型酶、硼酸盐转移配体和促进两个多阴离子RG - II分子接近的阳离子“伴侣”。电泳监测二聚化。欧芹茎部细胞壁酶不影响RG - II的体外二聚化。硼酸盐结合配体（apiose，脱氢抗坏血酸，醛醇）和小有机阳离子（包括多胺）也缺乏一致的效果。聚赖氨酸永久地与RG - II结合，妨碍了电泳分析。然而，另一种聚阳离子，多组氨酸，强烈地促进了RG - II被B(OH)3二聚化，而没有不可逆的多组氨酸- RG - II络合。同样，部分纯化的菠菜伸展蛋白（富含组氨酸/赖氨酸的阳离子糖蛋白），在体外强烈促进RG - II被B(OH)3二聚化。因此，某些多阳离子，包括多组氨酸和壁糖蛋白，可以陪伴RG‐II，操纵这种多阴离子多糖结构域，从而有利于硼桥接。这些伴侣在促进RG - II二聚化后与之分离，表明它们是催化作用而不是化学计量作用。我们提出了延伸蛋白- rg - II相互作用在指导细胞壁组装中的自然作用。
Dimerization of rhamnogalacturonan‐II (RG‐II) via boron cross‐links contributes to the assembly and biophysical properties of the cell wall. Pure RG‐II is efficiently dimerized by boric acid (B(OH)3) in vitro only if nonbiological agents for example Pb2+ are added. By contrast, newly synthesized RG‐II domains dimerize very rapidly in vivo. We investigated biological agents that might enable this. We tested for three such agents: novel enzymes, borate‐transferring ligands and cationic ‘chaperones’ that facilitate the close approach of two polyanionic RG‐II molecules. Dimerization was monitored electrophoretically. Parsley shoot cell‐wall enzymes did not affect RG‐II dimerization in vitro. Borate‐binding ligands (apiose, dehydroascorbic acid, alditols) and small organic cations (including polyamines) also lacked consistent effects. Polylysine bound permanently to RG‐II, precluding electrophoretic analysis. However, another polycation, polyhistidine, strongly promoted RG‐II dimerization by B(OH)3 without irreversible polyhistidine–RG‐II complexation. Likewise, partially purified spinach extensins (histidine/lysine‐rich cationic glycoproteins), strongly promoted RG‐II dimerization by B(OH)3 in vitro. Thus certain polycations, including polyhistidine and wall glycoproteins, can chaperone RG‐II, manoeuvring this polyanionic polysaccharide domain such that boron‐bridging is favoured. These chaperones dissociate from RG‐II after facilitating its dimerization, indicating that they act catalytically rather than stoichiometrically. We propose a natural role for extensin–RG‐II interaction in steering cell‐wall assembly.