DNA光复活作用机理的研究进展*

"环丁烷型嘧啶二聚体(Pyr< > Pyr) 是太阳光中紫外线造成DNA 损伤的主要光化学产物。DNA 光复活酶(或称光解酶) 能够利用可见光裂解二聚体的环丁烷环而修复DNA。本文对DNA 光复活过程中的光解酶对Pyr< > Pyr 的识别和光催化Pyr< > Pyr 裂解反应进行了综述, 介绍了DNA 光解酶的结构、DNA 的主要UV 光化学产物。较详尽地评述了国际上在光解酶催化二聚体裂解的途径以及模型研究方面的最新进展, 并预测了该领域的发展前景。     

酶蛋白直接修复嘧啶二聚体机理的模型研究

去辅基的DNA光解酶在280 nm光辐照下, 能高效修复底物嘧啶二聚体(Φ＝0.56). 为了模拟酶蛋白的这一修复过程, 合成了色氨酸(Trp)和/或酪氨酸(Tyr)与胸腺嘧啶二聚体(D)共价连接的化合物, 作为酶-底物复合物的模型, 研究了它们在295 nm光照射下氨基酸残基光敏化二聚体裂解的性质, 测定了二聚体裂解量子产率(Φ), 获得一些新的结果并对其进行了分析.     

色氨酸及其肽对cis-syn型1，3-二甲基胸腺嘧啶二聚体的光敏化裂解作用

通过荧光猝灭实验和测定二聚体裂解程度的辐照实验，研究色氨酸（Trp）及 其二肽色氨酰苯丙氨酸（Trp-Phe）对cis-syn型1，3-二甲基胸腺嘧啶二聚体（ DMTD）的光敏化裂解作用。结果表明，色氨酸及其二肽在较强光（λ > 290 nm） 辐照下，主要通过双光子电离生成的光合电子（e_(aq)~-）导致二聚体裂解，其次 ，通过激发单重态与二聚体间的电子转移导致二聚体裂解。另外一导致二聚体裂解 的可能途径：色氨酸残基激发三重态与二聚体间的电子转移光敏化二聚体裂解。     

DNA光解酶模型研究的近期进展

用模型化合物来模拟DNA光解酶与底物的作用, 有助于认识DNA光复活作用机理. 评述了环丁烷型嘧啶二聚体光解酶和(6-4)光产物光解酶的模型研究进展, 并展望了该领域的发展前景．     

手性金属配合物△,∧-[Ru(IP)2dppz]2+对含G:T错配的环丁烷嘧啶二聚体识别和部分构型修复的分子力学研究

环丁烷嘧啶二聚体(Cyclobutane Pyrimidine Dimer,CPD)是紫外线对DNA损伤导致皮肤癌的首要环节,XPC-hHR23B是最早作为对CPD的损伤识别剂的,但其识别效率很低.本文首次采用分子力学方法模拟了一种新的手性金属配合物△,∧-[Ru(IP)2dppz]2 对含G:T错配的CPD双螺旋DNA的识别作用.模拟结果显示:金属配合物[Ru(IP)2dppz]2 的两个手性异构体都对含G:T错配的CPD双螺旋DNA具有识别作用,识别的过程体现了很强的手性选择性、沟选择性和位点特异性.同时,我们发现:在∧-[Ru(IP)2dppz]2 插入到CPD后,形成CPD的两个T碱基由原来的敞口形状部分地转为近平行状,使其在构型上得到初步的修复.     

手性金属配合物Δ,Λ-[Ru(IP)_2dppz]~(2 )对含G:T错配的环丁烷嘧啶二聚体识别和部分构型修复的分子力学研究

环丁烷嘧啶二聚体(CyclobutanePyrimidineDimer,CPD)是紫外线对DNA损伤导致皮肤癌的首要环节,XPC-hHR23B是最早作为对CPD的损伤识别剂的,但其识别效率很低.本文首次采用分子力学方法模拟了一种新的手性金属配合物?,Λ-[Ru(IP)2dppz]2 对含G:T错配的CPD双螺旋DNA的识别作用.模拟结果显示:金属配合物[Ru(IP)2dppz]2 的两个手性异构体都对含G:T错配的CPD双螺旋DNA具有识别作用,识别的过程体现了很强的手性选择性、沟选择性和位点特异性.同时,我们发现:在Λ-[Ru(IP)2dppz]2 插入到CPD后,形成CPD的两个T碱基由原来的敞口形状部分地转为近平行状,使其在构型上得到初步的修复.     

手性金属配合物Δ,Λ-[Ru(IP)2dppz]2＋对含G:T错配的环丁烷嘧啶二聚体识别和部分构型修复的分子力学研究

环丁烷嘧啶二聚体(Cyclobutane Pyrimidine Dimer, CPD)是紫外线对DNA损伤导致皮肤癌的首要环节, XPC-hHR23B是最早作为对CPD的损伤识别剂的, 但其识别效率很低. 本文首次采用分子力学方法模拟了一种新的手性金属配合物Δ,Λ-[Ru(IP)₂dppz]^2＋对含G:T错配的CPD双螺旋DNA的识别作用. 模拟结果显示: 金属配合物[Ru(IP)₂dppz]^2＋的两个手性异构体都对含G:T错配的CPD双螺旋DNA具有识别作用, 识别的过程体现了很强的手性选择性、沟选择性和位点特异性. 同时, 我们发现: 在Λ-[Ru(IP)₂dppz]^2＋插入到CPD后, 形成CPD的两个T碱基由原来的敞口形状部分地转为近平行状, 使其在构型上得到初步的修复.     

手性金属配合物Δ,Λ-[Ru(IP)2dppz]2＋对含G:T错配的环丁烷嘧啶二聚体识别和部分构型修复的分子力学研究

环丁烷嘧啶二聚体(Cyclobutane Pyrimidine Dimer, CPD)是紫外线对DNA损伤导致皮肤癌的首要环节, XPC-hHR23B是最早作为对CPD的损伤识别剂的, 但其识别效率很低. 本文首次采用分子力学方法模拟了一种新的手性金属配合物Δ,Λ-[Ru(IP)₂dppz]^2＋对含G:T错配的CPD双螺旋DNA的识别作用. 模拟结果显示: 金属配合物[Ru(IP)₂dppz]^2＋的两个手性异构体都对含G:T错配的CPD双螺旋DNA具有识别作用, 识别的过程体现了很强的手性选择性、沟选择性和位点特异性. 同时, 我们发现: 在Λ-[Ru(IP)₂dppz]^2＋插入到CPD后, 形成CPD的两个T碱基由原来的敞口形状部分地转为近平行状, 使其在构型上得到初步的修复.     

木质素二聚体模型化合物热解机理的量子化学研究

β-O-4连接是木质素主体结构单元之间的主要联结方式。采用密度泛函理论方法B3LYP,在6-31G (d, p)基组水平上,对β-O-4型木质素二聚体模型化合物(1-愈创木基-2-(2-甲氧基苯氧基)-1,3丙二醇)的热解反应机理进行了研究。提出了三种热解反应途径:C_β-O键均裂的后续反应、C_α-C_β键均裂的后续反应以及协同反应。对各种反应的反应物、产物、中间体和过渡态的结构进行了能量梯度全优化,计算了各热解反应途径的标准动力学参数。分析了各种主要热解产物的形成演化机理以及热解过程中温度对热解机理的影响。计算结果表明,C_β-O键的均裂反应和协同反应路径(1)和(3)是木质素二聚体热解过程中主要的反应路径,而C_α-C_β键的均裂反应和协同反应路径(2)和(5)是主要的竞争反应路径;热解的主要产物是酚类化合物如愈创木酚、1-愈创木基-3-羟基丙酮、3-愈创木基-3-羟基丙醛、愈创木基甲醛和乙烯等。在热解低温阶段协同反应是热解过程中的主要反应形式,而在高温阶段自由基均裂反应是热解过程的主要反应形式。     

Kinetics and mechanism of electron-induced splitting of a cyclobutane pyrimidine dimer with or without an electron acceptor

DNA repair has received heightened attention in recent years as ozone depletion threatens to significantly increase DNA damage by UVB radiation[1—6]. The major lesions formed in DNA by this radiation are cis-syn cyclobutane pyrimidine dimers, which are created by the linkage of two neighboring pyrimidine bases in DNA via C5-C5 and C6-C6 atoms by [2+2] cycloaddition[2,5—8]. This potentially lethal or mutagenic damage can be repaired either by the removal of the damaged bases by excisio…     

Stabilization of the Triplet Biradical Intermediate of 5-Methylcytosine Enhances Cyclobutane Pyrimidine Dimer (CPD) Formation in DNA

Cyclobutane pyrimidine dimer (CPD) is a photoproduct formed by two stacked pyrimidine bases through a cycloaddition reaction upon irradiation. Owing to its close association with skin cancer, the mechanism of CPD formation has been studied thoroughly. Among many aspects of CPD, its formation involving 5-methylcytosine (5mC) has been of special interest because the CPD yield is known to increase with C5-methylation of cytosine. In this work, high-level quantum mechanics/molecular mechanics (QM/MM) calculations are used to examine a previously experimentally detected pathway for CPD formation in hetero (thymine-cytosine and thymine-5mC) dipyrimidines, which is facilitated through intersystem crossing in thymine and formation of a triplet biradical intermediate. A DNA duplex model system containing a core sequence TmCG or TCG is used. The stabilization of a radical center in the biradical intermediate by the methyl group of 5mC can lead to increased CPD yield in TmCG compared with its non-methylated counterpart, TCG, thereby suggesting the existence of a new pathway of CPD formation enhanced by 5mC.     

Oxidative Splitting of a Pyrimidine Cyclobutane Dimer:A Pulse Radiolysis Study

The oxidative splitting process of cis-syn 1,3-dimethyluracil cyclobutane dimer(DMUD) in aqueous solution was investigated using pulse radiolysis technique.The results indicated that DMUD can be splitted into 1,3-dimethyluracil(DMU) by OH radicals(OH) and Br2 radical anions(Br2^-),but not by azide radicals(N3^).The oxidative mechanisms that an H-abstracted from DMUD for OH oxidative splitting and an electron transfer from DMUD to Br2-,were suggested.Related kinetic parameters were determined.     

Very Low Energy Electrons Transform the Cyclobutane‐Pyrimidine Dimer into a Highly Reactive Intermediate

Electrons with virtually no kinetic energy (close to 0 eV) trigger the decomposition of cytotoxic cyclobutane‐pyrimidine dimer (CPD) into a surprisingly large variety of fragment ions plus their neutral counterparts. The response of CPD to low energy electrons is thus comparable to that of explosives like trinitrotoluene (TNT). The dominant unimolecular reaction is the splitting into two thymine like units, which can be considered as the essential molecular step in the photolyase of CPD. We find that CPD is significantly more sensitive towards low energy electrons than its thymine building blocks. It is proposed that electron attachment at very low energy proceeds via dipole bound states, supported by the large dipole moment of the molecule (6.2 D). These states act as effective doorways to dissociative electron attachment (DEA).     

Triplet-Induced Lesion Formation at CpT and TpC Sites in DNA

UV irradiation induces DNA lesions particularly at dipyrimidine sites. Using time-resolved UV pump (250 nm) and mid-IR probe spectroscopy the triplet pathway of cyclobutane pyrimidine dimer (CPD) formation within TpC and CpT sequences was studied. The triplet state is initially localized at the thymine base but decays with 30 ns under formation of a biradical state extending over both bases of the dipyrimidine. Subsequently this state either decays back to the electronic ground state on the 100 ns time scale or forms a cyclobutane pyrimidine dimer lesion (CPD). Stationary IR spectroscopy and triplet sensitization via 2′-methoxyacetophenone (2-M) in the UVA range shows that the lesions are formed with an efficiency of approximately 1.5 %. Deamination converts the cytosine moiety of the CPD lesions on the time scale of 10 hours into uracil which gives CPD(UpT) and CPD(TpU) lesions in which the coding potential of the initial cytosine base is vanished.