Mechanisms for Radiation Damage to DNA: LET Effects

描述(由申请人提供)： 我们的总体研究目标是阐明变化的线性能量转移(LET)辐射对DNA损伤的基本机制。我们的DNA辐射损伤综合模型描述了从最初的DNA离子自由基的形成，到空穴和电子转移，最后到分子产物的事件，将在每一步进行测试，以阐明DNA辐射损伤的基本过程。这些研究是在强调辐射直接影响的条件下进行的，将使用磁共振光谱、密度泛函理论和产物分析技术以及伽马和回旋重离子束照射。有五个目标：第一是表征DNA中的电子和空穴传输，它将集中在电子通过堆积碱基向已知氧化还原电位的插层物种转移的作用上。空穴转移将多个氧化损伤部位定位为单一鸟嘌呤碱基，从而提供辐射防护作用的假设也将得到检验。在我们的第二个目标中，我们将利用一项实验突破，允许清除辐射DNA中的空穴和电子，从而分离中性(主要是糖)自由基，并方便地调查这些物种的性质和身份。这是第一次有可能从自由基阶段的直接作用中识别和量化一些直接的链断裂过程。我们的第三个目标将通过研究DNA及其组分中的阳离子自由基激发态来测试高LET照射下糖自由基的形成机制。我们的第四个目标将使用磁共振技术来表征自由基(ESR，Endor)，并确定它们作为辐射沿辐射轨迹的LET的函数的空间分布和聚集(PELDOR)。我们捕获空穴和电子的能力使我们现在能够分离和比较低LET和高LET产生的中性自由基。我们的最终目标将使用理论计算来进一步测试和确认上述研究中提出的分子机制。最令人感兴趣的将是通过密度泛函理论对低能电子导致立即链断裂的假设进行测试。我们相信，这种集中的、合作的努力将使我们能够对生物医学研究的基本辐射过程建立新的理解。

DESCRIPTION (provided by applicant): Our overall research goal is to elucidate fundamental mechanisms of radiation damage to DNA by radiations of varying linear energy transfer (LET). Our comprehensive model for DNA radiation damage that describes events from the formation of the initial DNA ion radicals, to hole and electron transfer, finally to molecular products will be tested at each step to elucidate the fundamental processes for DNA radiation damage. These studies, which are performed under conditions that emphasize the direct effect of radiation, will employ magnetic resonance spectroscopies, density functional theory and product analysis techniques as well as gamma and cyclotron heavy ion beam irradiations. There are five aims: First is the characterization of electron and hole transport in DNA which will concentrate on the role of electron transfer through the stacked bases, to intercalated species of known redox potential. The hypothesis that hole transfer localizes multiple oxidative damage sites to single a guanine base and thereby provides a radioprotective effect will also be tested. In our second aim, we will make use of an experimental breakthrough that allows for scavenging of holes and electrons in irradiated DNA providing for the isolation of the neutral (mainly sugar) radicals and the facile investigation of the nature and identity of these species. For the first time, it may be possible to identify and quantitate a number of immediate strand break processes from the direct effect at the radical stage. Our third aim will test mechanisms of sugar radical formation likely with high LET irradiation by an investigation of cationic radical excited states within DNA and components. Our fourth aim will use magnetic resonance techniques to characterize radicals (ESR, ENDOR) and to ascertain their spatial distribution and clustering (PELDOR) as a function of the LET of the radiation along the radiation track. Our ability to capture both holes and electrons allows us, now, to isolate and compare low and high LET generated neutral radicals. Our final aim will employ theoretical calculations to further test and confirm molecular mechanisms proposed in the above studies. Of prime interest will be a test via density functional theory of the hypotheses that low energy electrons cause immediate strand breaks. We believe this focused, collaborative effort will allow us to establish new understandings of fundamental radiation processes for biomedical research.