THE ELECTROSTATIC POTENTIAL OF ESCHERICHIA-COLI DIHYDROFOLATE-REDUCTASE
THE ELECTROSTATIC POTENTIAL OF ESCHERICHIA-COLI DIHYDROFOLATE-REDUCTASE
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DOI：
10.1002/prot.340110102
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发表时间：
1991-01-01
期刊：
影响因子：
--
通讯作者：
HAGLER, AT
中科院分区：
文献类型：
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作者：
BAJORATH, J;KITSON, DH;HAGLER, AT
大肠杆菌二氢叶酸还原酶（DHFR）携带-10电子的净电荷，但它结合配体的净电荷为-4（NADPH）和-2（叶酸或二氢叶酸）。酶的静电势的评估和分析提供了关于如何实现这一点的见解。结果表明，除了配体结合位点之外，酶被整体负电位覆盖（如预期的那样），配体结合位点位于正电位的“口袋”内，使酶能够结合带负电荷的配体。静电势与酶中带电残基的不对称分布有关，这种不对称的电荷分布，沿着发生在溶剂-蛋白质界面的介电边界，类似于超氧化物歧化酶中发生的情况。因此，DHFR是另一种情况，其中活性位点的形状将电场集中到溶液中。大肠杆菌DHFR显示是在位置32、52和57处存在三个带正电荷的残基的直接结果-最近还显示这三个残基对配体叶酸的电子极化有显著贡献。后者被假定参与催化过程。一个类似的结构基序的三个带正电荷的氨基酸，产生一个积极的潜力，在入口处的活性位点也被发现在DHFR从鸡肝，并建议是一个共同的特点，在DHFR从许多物种。值得注意的是，尽管来自不同物种的DHF的净电荷从+3变化到-10，但是酶能够结合相同的带负电荷的配体，并且执行相同的催化功能。
Escherichia coli dihydrofolate reductase (DHFR) carries a net charge of -10 electrons yet it binds ligands with net charges of -4 (NADPH) and -2 (folate or dihydrofolate). Evaluation and analysis of the electrostatic potential of the enzyme give insight as to how this is accomplished. The results show that the enzyme is covered by an overall negative potential (as expected) except for the ligand binding sites, which are located inside "pockets" of positive potential that enable the enzyme to bind the negatively charged ligands. The electrostatic potential can be related to the asymmetric distribution of charged residues in the enzyme.The asymmetric charge distribution, along with the dielectric boundary that occurs at the solvent-protein interface, is analogous to the situation occurring in superoxide dismutase. Thus DHFR is another case where the shape of the active site focuses electric fields out into solution.The positive electrostatic potential at the entrance of the ligand binding site in E. coli DHFR is shown to be a direct consequence of the presence of three positively charged residues at positions 32, 52, and 57-residues which have also been shown recently to contribute significantly to electronic polarization of the ligand folate. The latter has been postulated to be involved in the catalytic process. A similar structural motif of three positively charged amino acids that gives rise to a positive potential at the entrance to the active site is also found in DHFR from chicken liver, and is suggested to be a common feature in DHFRs from many species. It is noted that, although the net charges of DHFRs from different species vary from +3 to -10, the enzymes are able to bind the same negatively charged ligands, and perform the same catalytic function.