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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Dissection of the triple tryptophan electron transfer chain in Escherichia coli DNA photolyase: Trp382 is the primary donor in photoactivation.
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Dissection of the triple tryptophan electron transfer chain in Escherichia coli DNA photolyase: Trp382 is the primary donor in photoactivation.

机译：解剖大肠杆菌DNA光解酶中的三色氨酸电子转移链：Trp382是光激活的主要供体。

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摘要

In Escherichia coli photolyase, excitation of the FAD cofactor in its semireduced radical state (FADH*) induces an electron transfer over approximately 15 A from tryptophan W306 to the flavin. It has been suggested that two additional tryptophans are involved in an electron transfer chain FADH* <-- W382 <-- W359 <-- W306. To test this hypothesis, we have mutated W382 into redox inert phenylalanine. Ultrafast transient absorption studies showed that, in WT photolyase, excited FADH* decayed with a time constant tau approximately 26 ps to fully reduced flavin and a tryptophan cation radical. In W382F mutant photolyase, the excited flavin was much longer lived (tau approximately 80 ps), and no significant amount of product was detected. We conclude that, in WT photolyase, excited FADH* is quenched by electron transfer from W382. On a millisecond scale, a product state with extremely low yield ( approximately 0.5% of WT) was detected in W382F mutant photolyase. Its spectral and kinetic features were similarto the fully reduced flavineutral tryptophan radical state in WT photolyase. We suggest that, in W382F mutant photolyase, excited FADH* is reduced by W359 at a rate that competes only poorly with the intrinsic decay of excited FADH* (tau approximately 80 ps), explaining the low product yield. Subsequently, the W359 cation radical is reduced by W306. The rate constants of electron transfer from W382 to excited FADH* in WT and from W359 to excited FADH* in W382F mutant photolyase were estimated and related to the donor-acceptor distances.
机译：在大肠杆菌光解酶中，处于半还原自由基状态（FADH *）的FAD辅因子的激发诱导了从色氨酸W306到黄素的大约15 A电子转移。已经建议在电子转移链FADH *≤W382≤W359≤W306中涉及另外两个色氨酸。为了验证该假设，我们将W382突变为氧化还原惰性苯丙氨酸。超快速瞬态吸收研究表明，在WT光裂解酶中，激发的FADH *以约26 ps的时间常数tau衰减，从而完全还原了黄素和色氨酸阳离子自由基。在W382F突变型光解酶中，激发的黄素的寿命更长（tau约为80 ps），并且未检测到大量产物。我们得出结论，在WT光裂解酶中，激发的FADH *被W382的电子转移淬灭。以毫秒为单位，在W382F突变型光裂解酶中检测到极低产率（约WT的0.5％）的产物状态。其光谱和动力学特征类似于WT光裂解酶中完全还原的黄素/中性色氨酸自由基状态。我们建议，在W382F突变型光解酶中，受激发的FADH *被W359还原的速率与受激发的FADH *的固有衰减（tau约80 ps）竞争性很弱，这说明了产品收率低。随后，W359阳离子自由基被W306还原。估计了从W382到WT中的W382激发的FADH *和从W359F突变型光裂解酶中的W359到激发的FADH *的电子转移速率常数，并与供体-受体距离相关。

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