Crystal structures of Escherichia coli and Lactobacillus casei dihydrofolate reductase refined at 1.7 A resolution. I. General features and binding of methotrexate.
Crystal structures of Escherichia coli and Lactobacillus casei dihydrofolate reductase refined at 1.7 A resolution. I. General features and binding of methotrexate.
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DOI：
10.2210/pdb3dfr/pdb
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发表时间：
1982-11
期刊：
影响因子：
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通讯作者：
J. Bolin;D. Filman;D. Matthews;R. Hamlin;J. Kraut
中科院分区：
文献类型：
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作者：
J. Bolin;D. Filman;D. Matthews;R. Hamlin;J. Kraut
X射线数据已扩展到1.7 A的大肠杆菌二氢叶酸还原酶与甲氨蝶呤和干酪乳杆菌二氢叶酸还原酶与甲氨蝶呤和NADPH的三元复合物的二元复合物。两种结构的模型已被细化为R因子为0.15，并包括固定和液体溶剂的参数。这两种二氢叶酸还原酶彼此相似，甚至比精制前认为的更接近。还发现了一些新的结构特征。其中包括连接Gly-97和Gly-98的顺式肽（L.酪蛋白编号），在这两个物种，α螺旋涉及残基43至50在E。大肠杆菌的酶，并存在什么可能是一个特定的水合部位暴露的α螺旋。改进导致甲氨蝶呤结合细节的修订描述。我们现在看到，一个固定的水分子介导甲氨蝶呤的2-氨基和Thr-116之间的相互作用（L。casei编号），并且抑制剂的4-氨基与酶形成两个氢键（而不是一个）。还讨论了其他修订。底物结合的一个假设的模型，提出了蝶啶环是颠倒的，而所有的蛋白质和溶剂原子保持固定。在该模型中，Asp-26与底物的2-氨基和N3形成氢键。
X-ray data have been extended to 1.7 A for a binary complex of Escherichia coli dihydrofolate reductase with methotrexate and a ternary complex of Lactobacillus casei dihydrofolate reductase with methotrexate and NADPH. Models for both structures have been refined to R factors of 0.15 and include parameters for fixed and liquid solvent. The two species of dihydrofolate reductase resemble one another even more closely than was thought to be the case prior to refinement. Several new structural features have also been discovered. Among them are a cis peptide linking Gly-97 and Gly-98 (L. Casei numbering) in both species, an alpha helix involving residues 43 through 50 in the E. coli enzyme, and the existence of what may be a specific hydration site on exposed alpha helices. Refinement has led to a revised description of the details of methotrexate binding. We now see that a fixed water molecule mediates the interaction between methotrexate's 2-amino group and Thr-116 (L. casei numbering) and that the inhibitor's 4-amino group makes two hydrogen bonds with the enzyme (instead of one). Other revisions are also discussed. A hypothetical model for substrate binding is proposed in which the pteridine ring is turned upside down while all protein and solvent atoms remain fixed. Asp-26 in this model is hydrogen bonded to the substrate's 2-amino group and to N3.