Centre of Advanced Study in Crystallography and Biophysics, University of Madras, Maraimalai (Guindy) Campus, Chennai, 600 025, India,
Protein J. 2013 Dec;32(8):649-56. doi: 10.1007/s10930-013-9528-8.
Endo-1,4-Xylanase II is an enzyme which degrades the linear polysaccharide beta-1,4-xylan into xylose. This enzyme shows highest enzyme activity around 55 °C, even without being stabilized by the disulphide bridges. A set of nine high resolution crystal structures of Xylanase II (1.11-1.80 Å) from Trichoderma reesei were selected and analyzed in order to identify the invariant water molecules, ion pairs and water-mediated ionic interactions. The crystal structure (PDB-id: 2DFB) solved at highest resolution (1.11 Å) was chosen as the reference and the remaining structures were treated as mobile molecules. These structures were then superimposed with the reference molecule to observe the invariant water molecules using 3-dimensional structural superposition server. A total of 37 water molecules were identified to be invariant molecules in all the crystal structures, of which 26 invariant molecules have hydrogen bond interactions with the back bone of residues and 21 invariant water molecules have interactions with side chain residues. The structural and functional roles of these water molecules and ion pairs have been discussed. The results show that the invariant water molecules and ion pairs may be involved in maintaining the structural architecture, dynamics and function of the Endo-1,4-Xylanase II.
内切-1,4-木聚糖酶 II 是一种能够将线性多糖β-1,4-木聚糖降解为木糖的酶。该酶在没有二硫键稳定的情况下，最适酶活温度约为 55°C。本研究选取了来自里氏木霉的内切-1,4-木聚糖酶 II 的九组高分辨率晶体结构（1.11-1.80Å），以鉴定不变水分子、离子对和水介导的离子相互作用。选择分辨率最高（1.11Å）的晶体结构（PDB-id：2DFB）作为参考，将其余结构视为可移动分子。然后使用三维结构叠加服务器将这些结构与参考分子进行叠加，以观察不变水分子。在所有晶体结构中，共鉴定出 37 个不变水分子，其中 26 个不变水分子与残基的骨架有氢键相互作用，21 个不变水分子与侧链残基相互作用。讨论了这些水分子和离子对的结构和功能作用。结果表明，不变水分子和离子对可能参与维持内切-1,4-木聚糖酶 II 的结构、动力学和功能。
