Understanding the biological rationale for the diversity of cellulose-directed carbohydrate-binding modules in prokaryotic enzymes
Understanding the biological rationale for the diversity of cellulose-directed carbohydrate-binding modules in prokaryotic enzymes
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DOI：
10.1074/jbc.m605903200
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发表时间：
2006-09-29
影响因子：
4.8
通讯作者：
Knox, J. Paul
中科院分区：
文献类型：
--
作者：
Blake, Anthony W.;McCartney, Lesley;Knox, J. Paul
植物细胞壁被糖苷水解酶降解，糖苷水解酶通常含有非催化碳水化合物结合模块 (CBM)，可增强降解。目前有 11 个基于序列的纤维素定向 CBM 家族；然而，这些蛋白质模块所表现出的结构多样性的生物学意义尚不确定。在这里，我们研究了八种纤维素结合 CBM 与细胞壁结合的能力。这些模块以结晶纤维素（A 型）为目标，位于家族 1、2a、3a 和 10（分别为 CBM1、CBM2a、CBM3a 和 CBM10）；无定形纤维素的内部区域（B 型；CBM4-1、CBM17、CBM28）；和纤维素链的末端（C 型；CBM9-2）。 A 型 CBM 与次生细胞壁结合特别有效，尽管它们也识别初生细胞壁。 A 型 CBM2a 和 CBM10 源自相同的酶，根据细胞类型、组织和来源分类单元，显示出与细胞壁的不同结合。 B 型 CBM 和 C 型 CBM 与细胞壁的结合比 A 型 CBM 弱得多。尽管这些 B 型模块在体外表现出与无定形纤维素类似的结合，但 CBM17 与细胞壁的结合比 CBM4-1 更广泛。芹菜厚角组织增厚的初生细胞壁显示出与某些 B 型模块的显着结合，表明在这些壁中纤维素链不会形成高度有序的晶体结构。切片的果胶酸裂合酶处理导致纤维素导向的 CBM 的结合增加，这表明果胶聚合物的纤维素微纤维的脱色可以增加 CBM 的进入。对不同来源细胞壁的差异识别为细胞壁水解酶中发生的纤维素定向 CBM 的多样性提供了生物学原理，并反过来揭示了初生和次生细胞壁中纤维素微结构的多样性。
Plant cell walls are degraded by glycoside hydrolases that often contain noncatalytic carbohydrate-binding modules (CBMs), which potentiate degradation. There are currently 11 sequence-based cellulose-directed CBM families; however, the biological significance of the structural diversity displayed by these protein modules is uncertain. Here we interrogate the capacity of eight cellulose-binding CBMs to bind to cell walls. These modules target crystalline cellulose (type A) and are located in families 1, 2a, 3a, and 10 (CBM1, CBM2a, CBM3a, and CBM10, respectively); internal regions of amorphous cellulose (type B; CBM4-1, CBM17, CBM28); and the ends of cellulose chains (type C; CBM9-2). Type A CBMs bound particularly effectively to secondary cell walls, although they also recognized primary cell walls. Type A CBM2a and CBM10, derived from the same enzyme, displayed differential binding to cell walls depending upon cell type, tissue, and taxon of origin. Type B CBMs and the type C CBM displayed much weaker binding to cell walls than type A CBMs. CBM17 bound more extensively to cell walls than CBM4-1, even though these type B modules display similar binding to amorphous cellulose in vitro. The thickened primary cell walls of celery collenchyma showed significant binding by some type B modules, indicating that in these walls the cellulose chains do not form highly ordered crystalline structures. Pectate lyase treatment of sections resulted in an increased binding of cellulose-directed CBMs, demonstrating that decloaking cellulose microfibrils of pectic polymers can increase CBM access. The differential recognition of cell walls of diverse origin provides a biological rationale for the diversity of cellulose-directed CBMs that occur in cell wall hydrolases and conversely reveals the variety of cellulose microstructures in primary and secondary cell walls.