The determination of binding constants of micellar-packaged gramicidin A by 13C-and 23Na-NMR

AbstractBased on the malonyl gramicidin A structure of a single-stranded head-to-head hydrogen bonded right-handed, β6.3-helix in dodecyl phosphocholine (DPC) lipid micelles (Jing et al. (1994) Biophys. J. 66, A353), the determination of cation binding sites for gramicidin A (GA) in DPC micelles becomes a significant step in the study of ion transport through the model channel. First, the investigation of cation binding sites in DPC micellar packaged gramicidin A was achieved by 13C-NMR experiments at 30°C using four C-13 labeled GA samples. Then, the analyses based on two different equations, one for single and one for double occupancy, were employed to evaluate the correct occupancy model for GA in DPC micelles. The results clearly indicate double occupancy to be correct for Na+ ion as well as for K+, Rb+, Cs+ and Tl+ ions. Finally, the binding constants for Na+ ion were also estimated by the measurement of the longitudinal relaxation time (T1) using 23Na-NMR of the same sample at the same temperature as used for the 13C-NMR study. The binding constants obtained from 23Na-NMR are essentially equivalent to those determined from the 13C-chemical shifts

Interaction of Human Nuclear Topoisomerase I with Guanosine Quartet-forming and Guanosine-rich Single-stranded DNA and RNA Oligonucleotides

International audienceHuman nuclear DNA topoisomerase I (top1) plays a crucial role in DNA replication, transcription, and chromosome condensation. In this study, we show that intra- and intermolecular guanosine quartets (G-quartets) can inhibit top1-mediated DNA cleavage at a high affinity site. Top1-mediated DNA cleavage was also inhibited by a 16-mer single-stranded oligodeoxynucleotide (ODN) containing a G-rich sequence (G(2)T(2)G(5)TG(2)TG(3)) and by its RNA equivalent, neither of which form G-quartet structures. A comparison of various single-stranded ODN for their ability to inhibit top1-mediated DNA cleavage indicated that G-rich sequences containing repeats of 2 or 3 consecutive guanines interspaced with thymines specifically inhibited top1. We also found that both single-stranded and G-quartet-forming ODNs bind to top1 without being cleaved by the enzyme. These results demonstrate that either DNA or RNA G-rich single-stranded and G-quartet-forming oligonucleotides can bind to top1 and prevent cleavage of duplex DNA

Modeling Adaptive Strategies on Maintaining Wheat-Corn Production and Reducing Net Greenhouse Gas Emissions under Climate Change

Climate change has posed serious challenges to food production and sustainable development. We evaluated crop yields, N2O emissions, and soil organic carbon (SOC) in a typical wheat–corn rotation system field on the North China Plain on a 50-year scale using the Denitrification–Decomposition (DNDC) model and proposed adaptive strategies for each climate scenarios. The study showed a good consistency between observations and simulations (R2 > 0.95 and nRMSE < 30%). Among the twelve climate scenarios, we explored ten management practices under four climate scenarios (3 °C temperature change: P/T−3 and P/T+3; 30% precipitation change: 0.7P/T and 1.3P/T), which have a significant impact on crop yields and the net greenhouse effect. The results revealed that changing the crop planting time (CP) and using cold-resistant (CR) varieties could reduce the net greenhouse effect by more than 1/4 without sacrificing crop yields under P/T−3. Straw return (SR) minimized the negative impact on yields and the environment under P/T+3. Fertigation (FG) and Drought-Resistant (DR) varieties reduced the net greenhouse effect by more than 8.34% and maintained yields under 0.7P/T. SR was most beneficial to carbon sequestration, and yields were increased by 3.87% under 1.3P/T. Multiple adaptive strategies should be implemented to balance yields and reduce the environmental burden under future climate change