Molecular basis for the selectivity and specificity of ligand recognition by the family 16 carbohydrate-binding modules from Thermoanaerobacterium polysaccharolyticum ManA
Molecular basis for the selectivity and specificity of ligand recognition by the family 16 carbohydrate-binding modules from Thermoanaerobacterium polysaccharolyticum ManA
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DOI：
10.1074/jbc.m706513200
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发表时间：
2008-05-02
影响因子：
4.8
通讯作者：
Nair, Satish K.
中科院分区：
文献类型：
--
作者：
Bae, Brian;Ohene-Adjei, Samuel;Nair, Satish K.
将复杂多糖水解成单糖的酶在结构上是模块化的，并且由与称为碳水化合物结合模块（CBMs）的靶向模块融合的单个或多个催化结构域组成。CBM以高亲和力结合其配体，并通过将酶靶向其底物来提高催化组分的效率。在这里，我们利用了多学科的方法来表征每一个的两个家庭16碳水化合物结合结构域组件的高活性的甘露聚糖酶从嗜热嗜热厌氧杆菌多糖。这些代表了家族16 CBM的第一晶体结构。量热分析表明，尽管这些CBM对β-1，4-连接的糖表现出高特异性，但它们可以结合纤维素多糖和甘露糖多糖。为了阐明这种特异性和选择性的分子基础，我们已经确定了两种CBM中的每一种以及与甘露五糖或纤维五糖结合的CBM 16 -1的二元复合物的高分辨率晶体结构。这些结果为配体识别提供了详细的分子见解，并为旨在扩大这些靶向模块的天然库的合理工程实验提供了框架。
Enzymes that hydrolyze complex polysaccharides into simple sugars are modular in architecture and consist of single or multiple catalytic domains fused to targeting modules called carbohydratebinding modules (CBMs). CBMs bind to their ligands with high affinity and increase the efficiency of the catalytic components by targeting the enzymes to its substrate. Here we utilized a multidisciplinary approach to characterize each of the two family 16 carbohydrate-binding domain components of the highly active mannanase from the thermophile Thermoanaerobacterium polysaccharolyticum. These represent the first crystal structures of family 16 CBMs. Calorimetric analysis showed that although these CBMs demonstrate high specificity toward beta-1,4-linked sugars, they can engage both cello- and manno-polysaccharides. To elucidate the molecular basis for this specificity and selectivity, we have determined high resolution crystal structures of each of the two CBMs, as well as of binary complexes of CBM16-1 bound to either mannopentaose or cellopentaose. These results provide detailed molecular insights into ligand recognition and yield a framework for rational engineering experiments designed to expand the natural repertoire of these targeting modules.