Intraprotein radical transfer during photoactivation of DNA photolyase
Intraprotein radical transfer during photoactivation of DNA photolyase
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DOI：
10.1038/35014644
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发表时间：
2000-06-01
期刊：
影响因子：
64.8
通讯作者：
Brettel, K
中科院分区：
文献类型：
--
作者：
Aubert, C;Vos, MH;Brettel, K
氨基酸自由基在许多酶促反应中起关键作用（1）。催化通常涉及蛋白质内自由基特征的转移，如在I类核糖核苷酸还原酶中，自由基转移发生在35埃以上，从酪氨酰基自由基到半胱氨酸（1-3）。目前还存在争议，这种远程转移是通过电子转移发生，然后释放质子以产生中性自由基，还是通过H原子转移发生，即电子和质子的同时转移（4-7），后一种机制避免了低介电蛋白质中电荷形成的能量成本（4，5），但它对结构变化的鲁棒性低于电子转移（7）。现有的实验数据并没有明确区分这些建议。我们利用时间分辨吸收光谱研究了大肠杆菌DNA光裂合酶（8-10）的光活化（光诱导黄素腺嘌呤二核苷酸辅因子的还原）机制。在这里，我们表明，激发黄素腺嘌呤二核苷酸自由基抽象电子从附近的色氨酸在30 ps。在随后的电子转移沿着一个链的三个色氨酸，最偏远的色氨酸（作为阳离子自由基）释放一个质子的溶剂在约300纳秒，表明电子转移发生前质子解离。类似的过程可能发生在光解酶样蓝光受体中。
Amino-acid radicals play key roles in many enzymatic reactions(1). Catalysis often involves transfer of a radical character within the protein, as in class I ribonucleotide reductase where radical transfer occurs over 35 Angstrom, from a tyrosyl radical to a cysteine(1-3). It is currently debated whether this kind of long-range transfer occurs by electron transfer, followed by proton release to create a neutral radical, or by H-atom transfer, that is, simultaneous transfer of electrons and protons(4-7), The latter mechanism avoids the energetic cost of charge formation in the low dielectric protein(4,5), but it is less robust to structural changes than is electron transfer(7). Available experimental data do not clearly discriminate between these proposals. We have studied the mechanism of photoactivation (light-induced reduction of the flavin adenine dinucleotide cofactor) of Escherichia coli DNA photolyase(8-10) using time-resolved absorption spectroscopy. Here we show that the excited flavin adenine dinucleotide radical abstracts an electron from a nearby tryptophan in 30 ps. After subsequent electron transfer along a chain of three tryptophans, the most remote tryptophan (as a cation radical) releases a proton to the solvent in about 300 ns, showing that electron transfer occurs before proton dissociation. A similar process may take place in photolyase-like blue-light receptors.