The refinement and the structure of the dimer of alpha-chymotrypsin at 1.67-A resolution.
The refinement and the structure of the dimer of alpha-chymotrypsin at 1.67-A resolution.
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α-胰凝乳蛋白酶二聚体的精修和结构，分辨率为 1.67-A。
DOI：
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发表时间：
1985
影响因子：
4.8
通讯作者：
A. Tulinsky
中科院分区：
文献类型：
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作者：
R. Blevins;A. Tulinsky
用Hendrickson程序（PROLSQ），用约束最小二乘法，在1.67-A的分辨率下对α-糜蛋白酶的pH 3.5构象异构体的不对称单元的两个分子进行了精制。最终的R因子为0.179（包括247个水分子）。独立分子的主链的折叠在实验误差内是相同的，但这通常不适用于侧链立体化学。由此我们得出结论，蛋白质结构的折叠基本上不依赖于其侧链的大部分详细立体化学。独立分子之间的界面区域的侧链显示出明显的不对称性。这种不对称性表明，动态和不对称的结构变化发生在低聚化的时候，导致更积极有利的相互作用的二聚体。α-糜蛋白酶的独立分子的结构与单体γ-糜蛋白酶的结构的比较显示，虽然三个分子的折叠基本上是相同的，但由于一般的灵活性，侧链立体化学中存在许多显著的差异。α-胰凝乳蛋白酶的特异性位点被有序的水分子占据，其方式与γ-胰凝乳蛋白酶和其他蛋白质相似。当底物与酶结合时，这些水分子中的一些被取代，而其他的似乎有助于识别和定位催化中的芳香侧链。
The two molecules of the asymmetric unit of the pH 3.5 conformer of alpha-chymotrypsin have been refined at 1.67-A resolution using restrained least squares methods with Hendrickson's program (PROLSQ). The final R factor is 0.179 (including 247 water molecules). The folding of the main chain of the independent molecules is the same within experimental error but the same does not generally apply to the side chain stereochemistry. From this we conclude that the folding of a protein structure is basically independent of most of the detailed stereochemistry of its side chains. The side chains of the interface region between the independent molecules display pronounced asymmetry. This asymmetry suggests that dynamic and asymmetrical structural changes take place at the time of oligomerization leading to more energetically favorable interactions for the dimer. Comparison of the structures of the independent molecules of alpha-chymotrypsin with the structure of monomeric gamma-chymotrypsin revealed that although the folding of the three molecules is essentially the same, numerous and significant differences pervade the side chain stereochemistry attributable to general flexibility. The specificity site of alpha-chymotrypsin is occupied by ordered water molecules in a similar way to gamma-chymotrypsin and other proteins. Some of these water molecules are displaced when substrate binds to the enzyme, while the others appear to help identify and position the aromatic side chain in catalysis.