The redox potential of selenocystine in unconstrained cyclic peptides
The redox potential of selenocystine in unconstrained cyclic peptides
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DOI：
10.1002/anie.199708831
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发表时间：
1997-05-02
期刊：
影响因子：
--
通讯作者：
Moroder, L
中科院分区：
文献类型：
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作者：
Besse, D;Siedler, F;Moroder, L
硒代半胱氨酸（Sec）可以被视为核糖体介导的蛋白质合成中的第21个氨基酸。['，它存在于许多原核和真核蛋白质中，大自然使用UGA终止密码子来指定这种硒代氨基酸的插入，而不是翻译后修饰机制。迄今为止发现的大多数硒蛋白都是氧化还原酶，其中硒醇功能的低 pK 值（Sec 为 5.73，Cys 为 8.53）赋予了独特的生化特性。然而，硒代半胱氨酸本身以及含硒代半胱氨酸的肽和蛋白质的氧化还原电位尚未确定。在本研究中，我们使用强还原性二硫醇二硫苏糖醇（DTT）作为参考氧化还原系统测量了肽结构中硒代胱氨酸的表观氧化还原电位。之前对脂肪族和芳香族硒醇的研究已经清楚地表明，硒醇的强酸性和由此产生的高亲核性是观察到硒醇在硫醇二硫化物中催化活性的原因 具有强还原性二硫的交换反应。‘~]这种氧化还原活性需要从二硒化物中再生催化硒醇，至少在某种程度上。事实上，发现二硒化物可以通过在 pH 7.6 的水溶液中强烈还原二硫醇（如 DTT）来还原，而单硫醇不能将二硒化物还原到任何显着程度。即使在含硒代胱氨酸的肽二聚体的情况下，这一点也得到了充分证实，在 pH 7.6 下，二聚体仅被 103 倍过量的谷胱甘肽部分还原。 r51 谷胱甘肽的部分还原显然足以在活细胞中维持适合其生物掺入硒蛋白的硒代半胱氨酸浓度。事实上，与
Selenocysteine (Sec) can be viewed as the 21st amino acid in terms of ribosome-mediated protein synthesis.[’, It is present in numerous prokaryotic and eukaryotic proteins, and nature uses the UGA termination codon to specify the insertion of this selenoamino acid rather than a posttranslational modification mechanism. Most of the selenoproteins identified so far are redox enzymes, in which the low pK, value of the selenol function (5.73 for Sec vs. 8.53 for Cys) confers unique biochemical properties. However, the redox potential of selenocysteine itself as well as of selenocysteine-containing peptides and proteins has not yet been determined. In the present study we measured the apparent redox potential of selenocystine in peptidic structures using the strongly reducing dithiol dithiotreitol (DTT) as reference redox system.Previous studies on aliphatic and aromatic selenols have clearly shown that the strong acidity and the resulting high nucleophilicity of selenols is responsible for the observed catalytic activity of selenols in thiol-disulfide interchange reactions with strongly reducing dithi~ ls.‘~] This redox activity requires regeneration of the catalytic selenol from the diselenide, at least to some extent. In fact, diselenides were found to be reduced by strongly reducing dithiols like DTT in aqueous solution at pH 7.6, L4] whereas monothiols cannot reduce diselenides to any significant extentc3’This was fully confirmed even in the case of a selenocystine-containing peptide dimer, which was only partially reduced with a 103-fold excess of glutathione at pH 7.6. r51 This partial reduction by glutathione is apparently sufficient to maintain in living cells a concentration of selenocysteine suitable for its bioincorporation into selenoproteins. In fact, with