Probing the Binding Requirements of Modified Nucleosides with the DNA Nuclease SNM1A

SNM1A is a nuclease that is implicated in DNA interstrand crosslink repair and, as such, its inhibition is of interest for overcoming resistance to chemotherapeutic crosslinking agents. However, the number and identity of the metal ion(s) in the active site of SNM1A are still unconfirmed, and only a limited number of inhibitors have been reported to date. Herein, we report the synthesis and evaluation of a family of malonate-based modified nucleosides to investigate the optimal positioning of metal-binding groups in nucleoside-derived inhibitors for SNM1A. These compounds include ester, carboxylate and hydroxamic acid malonate derivatives which were installed in the 5′-position or 3′-position of thymidine or as a linkage between two nucleosides. Evaluation as inhibitors of recombinant SNM1A showed that nine of the twelve compounds tested had an inhibitory effect at 1 mM concentration. The most potent compound contains a hydroxamic acid malonate group at the 5′-position. Overall, our studies advance the understanding of requirements for nucleoside-derived inhibitors for SNM1A and indicate that groups containing a negatively charged group in close proximity to a metal chelator, such as hydroxamic acid malonates, are promising structures in the design of inhibitors.     

Characterization of a Novel CaCO3-Forming Alkali-Tolerant Rhodococcus erythreus S26 as a Filling Agent for Repairing Concrete Cracks

Biomineralization, a well-known natural phenomenon associated with various microbial species, is being studied to protect and strengthen building materials such as concrete. We characterized Rhodococcus erythreus S26, a novel urease-producing bacterium exhibiting CaCO₃-forming activity, and investigated its ability in repairing concrete cracks for the development of environment-friendly sealants. Strain S26 grown in solid medium formed spherical and polygonal CaCO₃ crystals. The S26 cells grown in a urea-containing liquid medium caused culture fluid alkalinization and increased CaCO₃ levels, indicating that ureolysis was responsible for CaCO₃ formation. Urease activity and CaCO₃ formation increased with incubation time, reaching a maximum of 2054 U/min/mL and 3.83 g/L, respectively, at day four. The maximum CaCO₃ formation was achieved when calcium lactate was used as the calcium source, followed by calcium gluconate. Although cell growth was observed after the induction period at pH 10.5, strain S26 could grow at a wide range of pH 4–10.5, showing its high alkali tolerance. FESEM showed rhombohedral crystals of 20–60 µm in size. EDX analysis indicated the presence of calcium, carbon, and oxygen in the crystals. XRD confirmed these crystals as CaCO₃ containing calcite and vaterite. Furthermore, R. erythreus S26 successfully repaired the artificially induced large cracks of 0.4–0.6 mm width.     

Theoretical Study on the Photo-Oxidation and Photoreduction of an Azetidine Derivative as a Model of DNA Repair

Photocycloreversion plays a central role in the study of the repair of DNA lesions, reverting them into the original pyrimidine nucleobases. Particularly, among the proposed mechanisms for the repair of DNA (6-4) photoproducts by photolyases, it has been suggested that it takes place through an intermediate characterized by a four-membered heterocyclic oxetane or azetidine ring, whose opening requires the reduction of the fused nucleobases. The specific role of this electron transfer step and its impact on the ring opening energetics remain to be understood. These processes are studied herein by means of quantum-chemical calculations on the two azetidine stereoisomers obtained from photocycloaddition between 6-azauracil and cyclohexene. First, we analyze the efficiency of the electron-transfer processes by computing the redox properties of the azetidine isomers as well as those of a series of aromatic photosensitizers acting as photoreductants and photo-oxidants. We find certain stereodifferentiation favoring oxidation of the cis-isomer, in agreement with previous experimental data. Second, we determine the reaction profiles of the ring-opening mechanism of the cationic, neutral, and anionic systems and assess their feasibility based on their energy barrier heights and the stability of the reactants and products. Results show that oxidation largely decreases the ring-opening energy barrier for both stereoisomers, even though the process is forecast as too slow to be competitive. Conversely, one-electron reduction dramatically facilitates the ring opening of the azetidine heterocycle. Considering the overall quantum-chemistry findings, N,N-dimethylaniline is proposed as an efficient photosensitizer to trigger the photoinduced cycloreversion of the DNA lesion model.     

5-Hydroxymethyl-, 5-Formyl- and 5-Carboxydeoxycytidines as Oxidative Lesions and Epigenetic Marks

The four non-canonical nucleotides in the human genome 5-methyl-, 5-hydroxymethyl-, 5-formyl- and 5-carboxydeoxycytidine (mdC, hmdC, fdC and cadC) form a second layer of epigenetic information that contributes to the regulation of gene expression. Formation of the oxidized nucleotides hmdC, fdC and cadC requires oxidation of mdC by ten-eleven translocation (Tet) enzymes that require oxygen, Fe(II) and α-ketoglutarate as cosubstrates. Although these oxidized forms of mdC are widespread in mammalian genomes, experimental evidence for their presence in fungi and plants is ambiguous. This vagueness is caused by the fact that these oxidized mdC derivatives are also formed as oxidative lesions, resulting in unclear basal levels that are likely to have no epigenetic function. Here, we report the xdC levels in the fungus Amanita muscaria in comparison to murine embryonic stem cells (mESCs), HEK cells and induced pluripotent stem cells (iPSCs), to obtain information about the basal levels of hmdC, fdC and cadC as DNA lesions in the genome.     

提前期不确定条件下的预防性维修备件存储模型研究

在考虑预防性维修周期和提前期不确定的条件下,分别研究备件存储与其相关的维修费用、缺货费用、库存费用以及订购费用等四种费用之间的关系,明确了备件存储量对各项费用的影响.以各项费用总和最小化为目标,构建了提前期不确定条件下的预防性维修备件存储模型.通过备件存储模型的构建,对备件存储过程中的各项成本进行分析,以期对备件库存策略的确定给出一种解决方案.     

浅谈2015年诺贝尔化学奖:DNA的损伤修复

DNA是生物体发挥功能的遗传基础,随时都承受着来自体内或体外环境的各种压力。这些压力可以使DNA的化学结构发生变化,即产生"DNA损伤";如果这些损伤不能被及时修复,会对生命体产生严重的后果。为了应对这样的挑战,细胞存在一系列的DNA损伤修复机制;这些机制的存在使得基因组在很长的时间内得以稳定维持。2015年度诺贝尔化学奖授予了托马斯·林达尔、保罗·莫德里奇以及阿齐兹·桑贾尔,以表彰他们在DNA损伤修复研究领域的杰出贡献。本文简述了DNA损伤修复机制研究的发展历程及其与人类健康密不可分的联系。     

民机复合材料结构修理容限研究

论文对民用飞机复合材料结构的修理容限进行了研究.在分析相关概念的基础上,根据结构对飞机安全性的重要性对损伤部件进行分类,并用损伤检出概率来衡量损伤程度,对结构承载能力要求进行线性划分.接着在深入分析波音飞机公司修理指标的基础上,提出了修理容限量化的评估指标,为修理方案的制定和优化提供技术依据.最后介绍了结构修理评估及附加检查.     

新型稀土镁合金螺钉体内促骨修复及体外生物相容性研究

为测试新型稀土镁合金的生物相容性及降解产物致敏性; 评价新型稀土镁合金螺钉对骨伤模型的治疗效果, 基于NZ30K镁合金添加Mn元素制成新型稀土镁合金, 并通过后期加工制成不同规格的螺钉. 将稀土镁合金螺钉浸入磷酸盐缓冲液中制作浸提液, 于大鼠后肢背部皮下注射, 观察浸提液皮下致敏性. 将螺钉打磨制成圆片植入到大鼠皮下, 观察皮下降解产气情况, 以可吸收骨蜡作为对照同位置皮下植入. 建立兔骨损伤模型, 将稀土镁合金植入, 定期拍摄X光检查螺钉降解情况, 按照时间顺序分别于8周、12周、16周处死实验兔制作肝肾切片、骨切片, 评价肝肾毒性及体内降解情况; 同期以ZA75镁合金为基础添加0.3% Mn元素制成新镁合金, 作为对照组对比稀土镁合金对大鼠骨髓间充质干细胞成骨分化效果. 将浸提液过滤稀释后添加至细胞培养板中, 加入成骨诱导液培养, Westernblot蛋白电泳实验测定骨保护蛋白(OPG)表达情况. 新型稀土镁合金浸提液未表现出致敏性, 皮下降解结果显示植入初中期有气腔产生, 中后期气腔消失, 镁合金完全降解; 组织切片显示, 兔股骨螺钉植入在前中期有一定肝肾毒性, 植入中期促骨生长效果相较于前期更为明显, 植入后期未见明显肝肾毒性, 螺钉降解完全, 植入部位骨质增强; 兔股骨植入降解结果显示植入前期未观察到明显的促进骨生长效果, 螺钉与骨质嵌合紧密, 植入中期促骨生长修复效果呈现, 局部骨组织出现膨隆包裹住螺钉降解产物, 植入后期螺钉完全降解, 植入位置有一小孔未闭合, 股骨近端明显膨隆; 蛋白电泳实验显示, 新型稀土镁合金浸提液可增加OPG表达, 具有良好的生物相容性. 基于NZ30K开发的新型稀土镁合金在动物实验及细胞实验阶段表现出良好的生物相容性, 可为临床应用提供一定参考.     

考虑不完全检测的冲击模型最优维修策略

针对制造系统中设备检测不完全的情形,研究基于不完全检测的冲击模型的周期检测、维修联合策略．通过定期检测获知系统的劣化状态以进行必要的预防性维修．在假设系统是退化的且有k个不同故障状态的条件下,以最小化系统运行成本为目标,以检测周期T、系统更换前故障次数Ⅳ为联合决策变量,利用更新过程理论建立了系统平均费用率C（T,N）的数学模型,并且给出最优联合策略的数值算法．最后借助数值例子演示了该模型,分析了检测水平对系统运行成本的影响．     

Economic production quantity model with repair failure and limited capacity

We develop an economic production quantity (EPQ) model with random defective items and failure in repair. The existence of only one machine results with limited production capacity and shortages. The aim of this research is to derive the optimal cycle length, the optimal production quantity and the optimal back ordered quantity for each product so as to minimize the total expected cost (holding, shortage, production, setup, defective items and repair costs). The convexity of the model is derived and the objective function is proved convex. Two numerical examples illustrate the practical usage of the proposed method.