A MOLECULAR-MODEL FOR THE REDOX POTENTIAL DIFFERENCE BETWEEN THIOREDOXIN AND DSBA, BASED ON ELECTROSTATICS CALCULATIONS
A MOLECULAR-MODEL FOR THE REDOX POTENTIAL DIFFERENCE BETWEEN THIOREDOXIN AND DSBA, BASED ON ELECTROSTATICS CALCULATIONS
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DOI：
10.1006/jmbi.1995.0303
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发表时间：
1995-06-02
影响因子：
5.6
通讯作者：
WARWICKER, J
中科院分区：
文献类型：
--
作者：
GANE, PJ;FREEDMAN, RB;WARWICKER, J
已知硫氧还蛋白和DsbA的二硫键活性位点具有高度的结构同源性：然而，DsbA是比硫氧还蛋白强得多的氧化剂。DsbA和硫氧还蛋白之间的氧化还原电位差已被测量为160 mV，相当于在还原/氧化平衡中的15.4 kJ/mol的位移。静电学计算已被用来研究这两种蛋白质的还原形式的相对稳定性。模型计算表明，大部分DsbA和硫氧还蛋白之间的氧化还原电位差产生形式改变的暴露和电离的硫醇盐的还原形式的稳定化，支持以前的实验研究的基础上提出的建议。计算已被用来构建硫醇盐稳定的差异的分子模型。虽然特定的相互作用，如硫醇-NH 35（硫氧还蛋白）/33（DsbA），提供了大量的稳定在每个还原的蛋白质，硫氧还蛋白和DsbA之间的差异，预计驻留在几个侧链和主链基团一致行动。预测DsbA中的残基H32和Q97与DsbA和硫氧还蛋白共有的蛋白质结构域中的多肽骨架的大部分区域一起沿着起作用。增加硫醇盐稳定的肽偶极子建议产生改变的主链的处置，和DsbA的电场上的额外的蛋白质结构域的效果。肽偶极在一个区域内的约20个残基接近活性位点二硫化物的预测，有助于显着的氧化还原电位差。
The disulphide active sites of thioredoxin and DsbA are known to possess a high degree of structural homology: However, DsbA is a much stronger oxidant than thioredoxin. The redox potential difference between DsbA and thioredoxin has been measured to be 160 mV, equivalent to a shift of 15.4 kJ/mol in the reduced/oxidised equilibrium. Electrostatics calculations have been used to study the relative stabilities of the reduced forms of the two proteins. Model calculations suggest that much of the redox potential difference between DsbA and thioredoxin arises form altered stabilisation of the exposed and ionised thiolates of the reduced forms, supporting suggestions previously made on the basis of experimental studies. The calculations have been used to construct a molecular model for the difference in thiolate stabilisation. Although specific interactions, such as thiolate-NH 35 (thioredoxin)/33 (DsbA), provide substantial stabilisation in each reduced protein, the difference between thioredoxin and DsbA is predicted to reside in several side-chain and main-chain groups acting in concert. Residues H32 and Q97 in DsbA are predicted to contribute, along with substantial regions of the polypeptide backbone in the protein domain which is common to DsbA and thioredoxin. Increased thiolate stabilisation by the peptide dipoles is suggested to arise from altered main-chain disposition, and the effect of the additional protein domain of DsbA on the electric field. Peptide dipoles in a region of about 20 residues close to the active site disulphide are predicted to contribute significantly to the redox potential difference.