Satyanarayana L, Gaikwad Sushama M, Balkrishnan H, Suresh C G
Division of Biochemical Sciences, National Chemical Laboratory, Pune-411008. India.
Protein Pept Lett. 2013 Feb;20(2):125-32. doi: 10.2174/092986613804725271.
Structural information deduced from the new crystal form of xylanase from Bacillus sp (NCL 87-6-10) (ATBXYL- C) helped us to identify the active site and interpret the stability of the enzyme. The analysis of the tetragonal crystal structure of ATBXYL-C with a bound and cleaved xylotriose revealed the two glutamic acid residues in the structure that could act as nucleophile (Glu94) and base (Glu184) in the enzyme activity and also the tryptophan residues interacting with the substrate. The cleavage of xylotriose in the crystal showed xylobiose to be the major product. Intrinsic fluorescence of the enzyme showed the presence of tryptophans in partially exposed to the solvent at the active site and surface tryptophans in electropositive environment. The titration experiments with xylobiose and xylotriose revealed slightly enhanced preference for longer chain X3 compared with X2. The crystal structure also account for some of the factors, such as increased number of ionic interactions and additional interactions at the N-terminus, which contributed to increased alkalophilicity and thermostability of the enzyme.
从芽孢杆菌属（NCL 87-6-10）（ATBXYL-C）木聚糖酶的新晶体形式推导得到的结构信息，帮助我们确定了活性位点并解释了该酶的稳定性。对结合并裂解木三糖的ATBXYL-C四方晶体结构的分析，揭示了结构中的两个谷氨酸残基，它们在酶活性中可分别充当亲核试剂（Glu94）和碱（Glu184），还揭示了与底物相互作用的色氨酸残基。晶体中木三糖的裂解显示木二糖是主要产物。该酶的内源荧光表明，活性位点处部分暴露于溶剂中的色氨酸以及处于正电环境中的表面色氨酸存在。用木二糖和木三糖进行的滴定实验表明，与X2相比，对较长链X3的偏好略有增强。晶体结构还解释了一些因素，例如离子相互作用数量的增加以及N端的额外相互作用，这些因素导致了该酶嗜碱性和热稳定性的提高。
