Structure-Function Analysis of the Bacterial Expansin EXLX1
Structure-Function Analysis of the Bacterial Expansin EXLX1
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DOI：
10.1074/jbc.m111.225037
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发表时间：
2011-05-13
影响因子：
4.8
通讯作者：
Cosgrove, Daniel J.
中科院分区：
文献类型：
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作者：
Georgelis, Nikolaos;Tabuchi, Akira;Cosgrove, Daniel J.
我们利用 EXLX1（一种来自枯草芽孢杆菌的扩展蛋白）来研究其植物细胞壁结合和细胞壁松弛活性所必需的蛋白质特征。我们发现两个扩展蛋白结构域 D1 和 D2 需要连接才能实现壁延伸活性，并且 D2 通过 D2 表面上的不同残基介导 EXLX1 与整个细胞壁和纤维素的结合。与纤维素的结合是由三个芳香族残基介导的，这些芳香族残基线性排列在跨越 D1 和 D2 的假定结合表面上。这三个残基突变为丙氨酸消除了纤维素结合，并同时消除了通过细胞壁延伸或滤纸弱化测量的壁松动活性，但几乎不影响与整个细胞壁的结合，这是由位于其他 D2 表面上的碱性残基介导的。这些碱性残基突变为谷氨酰胺会降低细胞壁结合，但不会降低细胞壁松弛活性。我们建议结构域 D2 作为新碳水化合物结合模块家族 CBM63 的创始成员，但其在扩展蛋白活性中的功能显然不仅仅是将 D1 锚定到壁上。结构域 D1 的推定结合表面上的几个极性残基对于活性也很重要，尤其是 Asp82，其突变为丙氨酸或天冬酰胺完全消除了壁松动活性。基于这种细菌扩展蛋白的功能见解可以外推到植物扩展蛋白与细胞壁的相互作用。
We made use of EXLX1, an expansin from Bacillus subtilis, to investigate protein features essential for its plant cell wall binding and wall loosening activities. We found that the two expansin domains, D1 and D2, need to be linked for wall extension activity and that D2 mediates EXLX1 binding to whole cell walls and to cellulose via distinct residues on the D2 surface. Binding to cellulose is mediated by three aromatic residues arranged linearly on the putative binding surface that spans D1 and D2. Mutation of these three residues to alanine eliminated cellulose binding and concomitantly eliminated wall loosening activity measured either by cell wall extension or by weakening of filter paper but hardly affected binding to whole cell walls, which is mediated by basic residues located on other D2 surfaces. Mutation of these basic residues to glutamine reduced cell wall binding but not wall loosening activities. We propose domain D2 as the founding member of a new carbohydrate binding module family, CBM63, but its function in expansin activity apparently goes beyond simply anchoring D1 to the wall. Several polar residues on the putative binding surface of domain D1 are also important for activity, most notably Asp82, whose mutation to alanine or asparagine completely eliminated wall loosening activity. The functional insights based on this bacterial expansin may be extrapolated to the interactions of plant expansins with cell walls.