Femtosecond dynamics of flavoproteins:: Charge separation and recombination in riboflavine (vitamin B2)-binding protein and in glucose oxidase enzyme
Femtosecond dynamics of flavoproteins:: Charge separation and recombination in riboflavine (vitamin B2)-binding protein and in glucose oxidase enzyme
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DOI：
10.1073/pnas.211440398
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发表时间：
2001-10-09
影响因子：
11.1
通讯作者：
Zewail, AH
中科院分区：
文献类型：
--
作者：
Zhong, DP;Zewail, AH
黄素蛋白可以作为维生素B-2（核黄素）的疏水位点，或者在其他结构中，与催化反应（如葡萄糖氧化）的辅因子一起起作用。在这方面的贡献，我们报告直接观察的电荷分离和重组的黄素蛋白：核黄素结合蛋白和葡萄糖氧化酶。在飞秒分辨率下，我们观察到核黄素结合蛋白中色氨酸到核黄素的超快电子转移，有两个反应时间：约100 fs（86%组分）和700 fs（14%组分）。观察到的电荷复合发生在8 ps，作为探测的电荷分离态的衰变和基态的恢复。电荷分离和复合的时间尺度表明，动力学的局部结构紧密性发生得如此之快，效率超过99%。相比之下，在葡萄糖氧化酶中，黄素腺嘌呤二核苷酸和色氨酸/酪氨酸之间的电子转移需要更长的时间，1.8 ps（75%）和10 ps（25%）;相应的电荷重组发生在两个时间尺度上，30 ps和纳秒，效率仍然超过97%。这两种结构不同的蛋白质（属于同一家族）在时间尺度上的差异与功能上的差异相关：前者对维生素的疏水识别需要一个紧密结合的结构（超快动力学），而后者的氧化还原反应更倾向于形成电荷分离状态，这种状态的寿命足够长，可以有效地发生化学反应。最后，我们还研究了在不同的离子强度和变性剂浓度对蛋白质构象动力学的影响，并观察到疏水裂缝的急剧崩溃，相反，葡萄糖氧化酶的逐渐变化。
Flavoproteins can function as hydrophobic sites for vitamin B-2 (riboflavin) or, in other structures, with cofactors for catalytic reactions such as glucose oxidation. In this contribution, we report direct observation of charge separation and recombination in two flavoproteins: riboflavin-binding protein and glucose oxidase. With femtosecond resolution, we observed the ultrafast electron transfer from tryptophan(s) to riboflavin in the riboflavin-binding protein, with two reaction times: approximate to 100 fs (86% component) and 700 fs (14%). The charge recombination was observed to take place in 8 ps, as probed by the decay of the charge-separated state and the recovery of the ground state. The time scale for charge separation and recombination indicates the local structural tightness for the dynamics to occur that fast and with efficiency of more than 99%. In contrast, in glucose oxidase, electron transfer between flavin-adenine-dinucleotide and tryptophan(s)/tyrosine(s) takes much longer times, 1.8 ps (75%) and 10 ps (25%); the corresponding charge recombination occurs on two time scales, 30 ps and nanoseconds, and the efficiency is still more than 97%. The contrast in time scales for the two structurally different proteins (of the same family) correlates with the distinction in function: hydrophobic recognition of the vitamin in the former requires a tightly bound structure (ultrafast dynamics), and oxidation-reduction reactions in the latter prefer the formation of a charge-separated state that lives long enough for chemistry to occur efficiently. Finally, we also studied the influence on the dynamics of protein conformations at different ionic strengths and denaturant concentrations and observed the sharp collapse of the hydrophobic cleft and, in contrast, the gradual change of glucose oxidase.