Blake C C, Pulford W C, Artymiuk P J
J Mol Biol. 1983 Jul 5;167(3):693-723. doi: 10.1016/s0022-2836(83)80105-3.
The structure of the water in crystals of human and tortoise egg-white lysozyme, which contain about 350 and about 650 water molecules per protein molecule, respectively, has been studied by X-ray refinement at high resolution. In the crystals, 60 to 80% of the total water is represented by featureless electron density filling the crystal interstices, which can be modelled to a first approximation by a single-valued, smoothed electron density continuum. The number of ordered water molecules detected is 140 for human and 128 for tortoise. These ordered water molecules are either hydrogen-bonded to protein polar groups, or hydrogen-bonded to other bound water molecules, to form a single layer around the protein molecules. Estimates of the proportion of the protein surface covered by ordered water molecules have been obtained by contact area calculations, giving a lower limit of approximately 45%, an upper limit of approximately 85% and a "best" estimate of approximately 75%. Examination of the structure of the ordered water layer shows that it is probably not any other single regular structure, and suggests that there is a local ordering controlled by the nature of the protein surface. Nearly all exposed protein polar atoms interact with ordered water molecules with, on average, protein oxygen atoms interacting with twice as many water molecules as protein nitrogen atoms. Analysis of the relation of the B-factors of the bound water molecules to the B-factors of the protein atoms to which they are bound, suggests that the 33 to 35 water molecules that make multiple hydrogen bonds with the lysozyme molecules are strongly bound, and that the 95 to 105 waters that make single hydrogen bonds to the protein or other bound water molecules are more weakly bound. Comparison of the location of the bound water molecules in the two lysozymes shows that most of the multiply bound water molecules occupy similar binding sites, suggesting that crystal packing or the presence of salt ions does not have a dominating influence on the protein-water interaction, which therefore may correspond to that in solution.
人源和龟源蛋清溶菌酶晶体中的水结构已通过高分辨率X射线精修进行了研究，其中人源和龟源蛋清溶菌酶晶体中每个蛋白质分子分别约含有350和650个水分子。在这些晶体中，总水量的60%至80%表现为填充晶体间隙的无特征电子密度，这可以通过单值、平滑的电子密度连续体进行一阶近似建模。检测到的有序水分子数量，人源为140个，龟源为128个。这些有序水分子要么与蛋白质极性基团形成氢键，要么与其他结合水分子形成氢键，从而在蛋白质分子周围形成单层。通过接触面积计算得出了有序水分子覆盖蛋白质表面比例的估计值，下限约为45%，上限约为85%，“最佳”估计约为75%。对有序水层结构的研究表明，它可能不是任何其他单一的规则结构，并表明存在由蛋白质表面性质控制的局部有序性。几乎所有暴露的蛋白质极性原子都与有序水分子相互作用，平均而言，蛋白质氧原子与水分子相互作用的数量是蛋白质氮原子的两倍。对结合水分子的B因子与其所结合的蛋白质原子的B因子之间关系的分析表明，与溶菌酶分子形成多个氢键的33至35个水分子结合紧密，而与蛋白质或其他结合水分子形成单个氢键的95至105个水分子结合较弱。对两种溶菌酶中结合水分子位置的比较表明，大多数多重结合的水分子占据相似的结合位点，这表明晶体堆积或盐离子的存在对蛋白质-水相互作用没有主导影响，因此这可能与溶液中的情况相对应。
