A new structural insight into XPA–DNA interactions

XPA (xeroderma pigmentosum group A) protein is an essential factor for NER (nucleotide excision repair) which is believed to be involved in DNA damage recognition/verification, NER factor recruiting and stabilization of repair intermediates. Past studies on the structure of XPA have focused primarily on XPA interaction with damaged DNA. However, how XPA interacts with other DNA structures remains unknown though recent evidence suggest that these structures could be important for its roles in both NER and non-NER activities. Previously, we reported that XPA recognizes undamaged DNA ds/ssDNA (double-strand/single-strandDNA) junctions with a binding affinity much higher than its ability to bind bulky DNA damage. To understand how this interaction occurs biochemically we implemented a structural determination of the interaction using a MS-based protein footprinting method and limited proteolysis. By monitoring surface accessibility of XPA lysines to NHS-biotin modification in the free protein and the DNA junction-bound complex we show that XPA physically interacts with the DNA junctions via two lysines, K168 and K179, located in the previously known XPA(98–219) DBD (DNA-binding domain). Importantly, we also uncovered new lysine residues, outside of the known DBD, involved in the binding. We found that residues K221, K222, K224 and K236 in the C-terminal domain are involved in DNA binding. Limited proteolysis analysis of XPA–DNA interactions further confirmed this observation. Structural modelling with these data suggests a clamp-like DBD for the XPA binding to ds/ssDNA junctions. Our results provide a novel structure-function view of XPA–DNA junction interactions.     

Temporal and spatial distribution of ammonia-oxidizing organisms of two types of wetlands in Northeast China

Applied Microbiology and Biotechnology - Ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) contribute significantly to the nitrogen cycle. The community structure of AOA and AOB...     

Beauty Matters: Social Preferences in a Three-Person Ultimatum Game

Preference for beauty is human nature, as previous behavior studies have supported the notion of “beauty premium” in which attractive people were more easily to get promoted and receive higher salaries. In the present study, 29 males were recruited to participate in a three-person ultimatum game (UG) including a proposer, a responder and a powerless third player. Each subject, playing as the responder, had to decide whether to accept an offer from the allocator both for himself and a female third person. We aimed to elucidate how the facial attractiveness of the female subject affected the male subjects’ fairness and decision-making in social exchanges. Frontal feedback-related negativity (FRN) in response to four offers in an attractive-face condition revealed no significant differences between offers; however, when the companion was an unattractive female, an “unfair/fair” offer, which assigned a lower share to the responder and a fair share to the third player, elicited the largest FRN. Furthermore, when the third player was offered the smallest amount (“fair/unfair” offer), a larger FRN was generated in an attractive-face condition than unattractive-face condition. In the “unfair/fair” offer condition in which subjects received a smaller allocation than the third person, the beauty of their female counterparts attenuated subjects’ aversion to inequality, resulting in a less negative FRN in the frontal region and an increased acceptance ratio. However, the influence of the third player’s facial attractiveness only affected the early evaluation stage: late P300 was found to be immune to the “beauty premium”. Under the two face conditions, P300 was smallest following an “unfair/fair” offer, whereas the amplitudes in the other three offer conditions exhibited no significant differences. In addition, the differentiated neural features of processing facial attractiveness were also determined and indexed by four event-related potentials (ERP) components: N170, frontal N1, N2 and late positive potentials (LPPs).     

Multiple mechanisms contributed to the reduced stability of Inner Mongolia grassland ecosystem following nitrogen enrichment

Plant and Soil - Global nitrogen enrichment has been identified as a major environmental problem that poses a threat to ecosystem functioning. However, there is no consensus on the impact of...     

Cholesterol modulates function of connexin 43 gap junction channel via PKC pathway in H9c2 cells

It has been shown that cholesterol modulates activity of protein kinase C (PKC), and PKC phosphorylates connexin 43 (Cx43) to regulate its function, respectively. However, it is not known whether cholesterol modulates function of Cx43 through regulating activity of PKC. In the present study, we demonstrated that cholesterol enrichment reduced the dye transfer ability of Cx43 in cultured H9c2 cells. Western blot analysis indicated that cholesterol enrichment enhanced the phosphorylated state of Cx43. Immunofluorescent images showed that cholesterol enrichment made the Cx43 distribution from condensed to diffused manner in the interface between the cells. In cholesterol enriched cells, PKC antagonists partially restored the dye transfer ability among the cells, downregulated the phosphorylation of Cx43 and redistributed Cx43 from the diffused manner to the condensed manner in the cell interface. In addition, reduction of cholesterol level suppressed PKC activity to phosphorylate Cx43 and restored Cx43 function in PKC agonist-treated cells. Furthermore, we demonstrated that cholesterol enrichment upregulated the phosphorylated state of Cx43 at Ser368, while PKC antagonists reversed the effect. Taken together, cholesterol level in the cells plays important roles in regulating Cx43 function through activation of the PKC signaling pathway.     

Inorganic and Organic Nitrogen Acquisition by a Fern Dicranopteris dichotoma in a Subtropical Forest in South China

The fern Dicranopteris dichotoma is an important pioneer species of the understory in Masson pine (Pinus massoniana) forests growing on acidic soils in the subtropical and tropical China. To improve our understanding of the role of D. dichotoma in nitrogen (N) uptake of these forests, a short-term ¹⁵N experiment was conducted at mountain ridge (MR, with low N level) and mountain foot (MF, with high N level). We injected ¹⁵N tracers as ¹⁵NH₄, ¹⁵NO₃ or ¹⁵N-glycine into the soil surrounding each plant at both MR and MF sites. Three hours after tracer injection, the fern D. dichotoma took up ¹⁵NH₄ ⁺ significantly faster at MF than at MR, but it showed significantly slower uptake of ¹⁵NO₃ ⁻ at MF than at MR. Consequently, ¹⁵NO₃ ⁻ made greater contribution to the total N uptake (50% to the total N uptake) at MR than at MF, but ¹⁵N-glycine only contributed around 11% at both sites. Twenty-four hours after tracer injection, D. dichotoma preferred ¹⁵NH₄ ⁺ (63%) at MR, whereas it preferred ¹⁵NO₃ ⁻ (47%) at MF. We concluded that the D. dichotoma responds distinctly in its uptake pattern for three available N species over temporal and spatial scales, but mainly relies on inorganic N species in the subtropical forest. This suggests that the fern employs different strategies to acquire available N which depends on N levels and time.     

Covalently linking the Escherichia coli global anaerobic regulator FNR in tandem allows it to function as an oxygen stable dimer

Glutathione (GSH) serves as an important anti-oxidant in the brain by scavenging harmful reactive oxygen species that are generated during different molecular processes. The GSH level in the brain provides indirect information on oxidative stress of the brain. We report in vivo detection of GSH non-invasively from various brain regions (frontal cortex, parietal cortex, hippocampus and cerebellum) in bilateral hemispheres of healthy male and female subjects and from bi-lateral frontal cortices in patients with mild cognitive impairment (MCI) and Alzheimer's disease (AD). All AD patients who participated in this study were on medication with cholinesterase inhibitors. Healthy young male (age 26.4±3.0) and healthy young female (age 23.6±2.1) subjects have higher amount of GSH in the parietal cortical region and a specific GSH distribution pattern (parietal cortex>frontal cortex>hippocampus ~ cerebellum) has been found. Overall mean GSH content is higher in healthy young female compared to healthy young male subjects and GSH is distributed differently in two hemispheres among male and female subjects. In both young female and male subjects, statistically significant (p=0.02 for young female and p=0.001 for young male) difference in mean GSH content is found when compared between left frontal cortex (LFC) and right frontal cortex (RFC). In healthy young female subjects, we report statistically significant positive correlation of GSH content between RFC and LFC (r=0.641, p=0.004) as well as right parietal cortex (RPC) and left parietal cortex (LPC) (r=0.797, p=0.000) regions. In healthy young male subjects, statistically significant positive correlation of GSH content was observed between LFC and LPC (r=0.481, p=0.032) regions. This statistical analysis implicates that in case of a high GSH content in LPC of a young male, his LFC region would also contain high GSH and vice versa. The difference in mean of GSH content between healthy young female control and female AD patients in RFC region (p=0.003) and difference in mean of GSH content between healthy young male control and male AD patients (p=0.05) in LFC region is found to be statistically significant. It is the first scientific report correlating alteration (in selective brain regions) of GSH level with clinical status of male and female subjects using non-invasive imaging technique.     

退耕区域发展碳汇产业的生态经济学思考

碳汇产业,即利用植物吸收二氧化碳的潜力及规律,在人工适度干预下获得清洁空气、满足人们生产和生活对生态环境需求的产业,为原有相对均衡或稳定的农业产业-资源系统的优化升级提供突破口和新的增长点.退耕区域生态系统服务中,固碳释氧功能的经济显化、碳汇潜力的迅速提高,以及国内外碳汇交易与碳汇市场的兴起等,为碳汇产业的发展奠定了理论和现实基础.随着碳汇产业的发展,生产经营者必然以提高碳汇产出为核心,形成对碳源的控制及对碳贮量增加路径的开发,重新布局农业产业-资源结构,因而为退耕区域可持续发展带来新的活力;同时,也隐含了下一步需要研发的重点,即碳汇产业融入后的农业产业-资源的配置结构及良性耦合机制.