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首页> 外文期刊>Biochemistry >Electrostatic effects of surface acidic amino acid residues on the oxidation-reduction potentials of the flavodoxin from Desulfovibrio vulgaris (Hildenborough).
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Electrostatic effects of surface acidic amino acid residues on the oxidation-reduction potentials of the flavodoxin from Desulfovibrio vulgaris (Hildenborough).

机译：表面酸性氨基酸残基对寻常脱硫弧菌（希尔登伯勒）的黄酮毒素的氧化还原电位的静电作用。

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摘要

The flavodoxin from Desulfovibrio vulgaris (Hildenborough) is a member of a family of small, acidic proteins that contain a single noncovalently bound flavin mononucleotide (FMN) cofactor. These proteins function as low-potential one-electron transferases in bacteria. A distinguishing feature of these flavoproteins is the dramatic decrease in the midpoint potential of the semiquinone/hydroquinone couple of the FMN upon binding to the apoprotein (-172 mV for FMN free in solution versus -443 mV when bound), a perturbation thought to be essential for physiological function. The structural basis of this phenomenon is not yet thoroughly understood. In this study, the contribution of six acidic residues (Asp62, Asp63, Glu66, Asp95, Glu99, and Asp106) to the perturbation of the redox properties of the cofactor has been investigated. These residues are clustered about the FMN binding site within 13 A of the N(1) atom of the cofactor. Using oligonucleotide-directed mutagenesis, these residues were neutralized in various combinations through the substitution of asparagine for aspartate and glutamine for glutamate. Seventeen mutant flavodoxins were generated in which one to all six acidic residues were systematically neutralized, often in various spatial configurations. There was no obvious correlation between the midpoint potentials for the oxidized/semiquinone couple and general electrostatic environment, although some differences were noted. However, the midpoint potential for the semiquinone/hydroquinone couple for each of the mutants was less negative than that of the wild type. These increases are strongly correlated with the number of acid to amide substitutions, with an average contribution of about 15 mV per substitution. Collectively, the unfavorable electrostatic environment provided by these acidic residues accounts for approximately one-third of the large midpoint potential shift for the semiquinone/hydroquinone couple that typifies the flavodoxin family, apparently through the destabilization of the flavin hydroquinone anion.
机译：寻常脱硫弧菌（希尔登伯勒）中的黄素毒素是一个小的酸性蛋白质家族的成员，这些蛋白质包含一个非共价结合的黄素单核苷酸（FMN）辅因子。这些蛋白质在细菌中充当低电势的单电子转移酶。这些黄素蛋白的一个显着特征是与脱辅基蛋白结合后，FMN的半醌/氢醌对的中点电位急剧降低（溶液中游离的FMN为-172 mV，结合时为-443 mV），这被认为是一种扰动。对生理功能至关重要。这种现象的结构基础尚未完全了解。在这项研究中，已经研究了六个酸性残基（Asp62，Asp63，Glu66，Asp95，Glu99和Asp106）对辅因子氧化还原特性的影响。这些残基聚集在辅因子N（1）原子13 A内的FMN结合位点附近。使用寡核苷酸定向诱变，通过将天冬酰胺替换为天冬氨酸，将谷氨酰胺替换为谷氨酸以各种组合中和这些残基。产生了十七种突变型黄素毒素，其中六个酸残基中的一个到全部被系统中和，通常以各种空间构型被中和。尽管注意到了一些差异，但氧化/半醌对的中点电势与一般静电环境之间没有明显的相关性。然而，每个突变体的半醌/对苯二酚对的中点电势比野生型负电势小。这些增加与酸被酰胺取代的数量密切相关，每个取代的平均贡献约为15 mV。总的来说，这些酸性残基提供的不利的静电环境约占代表黄酮毒素家族的半醌/氢醌对的大中点电势位移的三分之一，这显然是由于黄素氢醌阴离子的去稳定作用。

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