多肽Trp-Pro_(n)-Tyr中色氨酸和酪氨酸之间的超快质子耦合电子转移

Ultrafast Proton Coupled Electron Transfer between Tryptophan and Tyrosine in Peptides Trp-Pro_(n)-Tyr

本文使用稳态吸收与荧光光谱、纳秒时间分辨荧光光谱和飞秒时间分辨瞬态吸收光谱技术,在pH=3、7和10的三种条件下,全面研究了一系列模型多肽(Trp-Pro_(n)-Tyr,WPnY,n=0、1、2、3、5)中色氨酸(Trp,W)和酪氨酸(Tyr,Y)之间的超快质子耦合电子转移特性:研究发现多肽中色氨酸的荧光猝灭程度与肽链的长度呈负相关.在WPY中,色氨酸的荧光被强烈猝灭,并且这种猝灭效应与pH值高度相关.稳态吸收光谱表明,WPY中存在与其他模型多肽明显不同的缺色性;瞬态吸收光谱也展现出其激发态衰减比其他模型多肽更快,尤其是在pH=10时,这可能归因于色氨酸和酪氨酸之间高效的质子耦合电子转移效应.由于WPY中色氨酸和酪氨酸之间的距离极短,两个氨基酸之间发生了偶极相互作用,从而实现了酪氨酸向色氨酸“直接式”的质子和电子转移过程。其他模型多肽中,两个氨基酸之间的距离较远,只能发生缓慢和长程的“间接式”质子和电子转移.此外,本文对WY和WP二肽的研究结果进一步表明,色氨酸可能与多肽的肽骨架或脯氨酸之间还存在更复杂的相互作用:该研究为色氨酸-酪氨酸“二联体”中的电子和质子转移机制提供了实验证据,可以帮助人们了解蛋白质中色氨酸自由基的清除机制,也为进一步研究蛋白质的抗氧化自我保护功能提供了指导意义。

Aseriesofmodel peptides(Trp-Pro_(n)-Tyr,WPnY,n=0,1,2,3,5),which contain tryptophan(Trp,W),tyrosine(Tyr,Y),and proline(Pro,P),have been studied under three typical pH conditions(3,7,and 10)by steady-state absorptionand fluorescencespectroscopy,nanosecond time-resolved fluorescence and femtosecond timeresolved transient absorption spectroscopy.When the peptide's chain length is increased,Trp fluorescence quenching is expected to be gradually weakened.However,Trp fluorescence in WPY is strongly quenched and reveals even stronger quenching with increasing pH values,whose hypochromicity is clearly different from other model peptides.Transient absorption spectra also demonstrate that the excited state decay of WPY is much faster than that of other model peptides,especially at pH=10.It is attributed to the efficient proton coupled electron transfer(PCET)between Trp and Tyr.Moreover,due to the very short distance between Trp and Tyr in WPY,this PCET process could be achieved by "direct transfer",contrasted with the slow and long-range PCET process in other model peptides.Our results of the dipeptides WY and WP further suggest that Trp may also have more complex interactions with the peptide backbone or proline in those peptides.This work provides an experimental evidence for the electron transfer mechanism in WY dyads,which can help ones to understand how to reduce Trp radicals in proteins.