Numerical study of the auroral particle transport in the polar upper atmosphere

Starting from the Boltzmann equation and with some reasonable assumptions, a one-dimensional transport equation of charged energetic particles is derived by taking account of major interactions with neutral species in the upper atmosphere, including the processes of elastic scattering, the excitation, the ionization and the secondary electron production. The transport equation is numerically solved, for a simplified atmosphere consisting only of nitrogen molecules (N₂), to obtain the variations of incident electron fluxes as a function of altitude, energy and pitch angle. The model results can describe fairly the transport characteristics of precipitating auroral electron spectra in the polar upper atmosphere; meanwhile the N2 ionization rates calculated from the modeled differential flux spectra also exhibit good agreements with existing empirical models in terms of several key parameters. Taking the energy flux spectra of precipitating electrons observed by FAST satellite flying over EISCAT site on May 15, 1997 as model inputs, the model-calculated ionization rate profile of neutral atmosphere consists reasonably with that reconstructed from electron density measurements by the radar. Supported by the National Natural Science Foundation of China (Grant Nos. 40404015, 40390150), the Ministry of Science and Technology of PRC (Grant No. 2006BAB18B06) and Key Lab of Geospace Environment and Geodesy, Ministry of Education of PRC     

Long Residence Times Revealed by Aurora A Kinase‐Targeting Fluorescent Probes Derived from Inhibitors MLN8237 and VX‐689

We report the development of three fluorescent probes for protein kinase Aurora A that are derived from the well‐known inhibitors MLN8237 and VX‐689 (MK‐5108). Two of these probes target the ATP site of Aurora A, and one targets simultaneously the ATP and substrate sites of the kinase. The probes were tested in an assay with fluorescence polarisation/anisotropy readout, and we demonstrated slow association kinetics and long residence time of the probes (k_on 10⁵–10⁷ M ^?1 s^?1, k_off 10^?3–10^?4 s^?1; residence time 500–3000 s). The presence of the Aurora A activator TPX2 caused a significant reduction in the on‐rate and increase in the off‐rate of fluorescent probes targeting ATP site. These observations were supported by Aurora A inhibition assays with MLN8237 and VX‐689. Overall, our results emphasise the importance of rational design of experiments with these compounds and correct interpretation of the obtained data.     

Truncation and Optimisation of Peptide Inhibitors of Cyclin‐Dependent Kinase 2‐Cyclin A Through Structure‐Guided Design

Peptides that inhibit cyclin‐dependent kinase 2 by blocking the macromolecular substrate recruitment site of cyclin A were simplified, for example, by replacement of dipeptide units with β‐amino acids. The smallest inhibitor retaining activity was a tripeptide, whose binding mode was confirmed by X‐ray crystallography. This result suggests that nonpeptidic cyclin groove inhibitors may be feasible therapeutic agents.

     

用激酶抑制剂法筛选球等鞭金藻抗肿瘤活性物质

酪蛋白激酶(Protein Tyrosine Kinases,PTKs)在细胞信号转导途径中起到关键作用,已成为新型抗肿瘤活性物质的重要靶点。实验采用激酶抑制剂法对球等鞭金藻(Isochrysis galbana)的乙酸乙酯、丙酮、正戊醇和水的溶剂萃取物进行检测,结果显示,正戊醇萃取物有较明显的激酶抑制剂活性,抑制率为38.94%;对该萃取物进行薄层层析分离,以丙酮-石油醚(1∶60,v/v)为展开系统,得到Rf值为0.6610的组分,该组分对PTKs具有抑制作用,抑制率为32.21%;对此组分进行硅胶柱层析,以丙酮作为洗脱剂得到的分离组分对PTKs具有强烈的抑制作用,抑制率为86.09%,该组分同时显示出较强的细胞毒活性,这个结果预示着该组分可能是球等鞭金藻中的目的活性物质;同时,激酶抑制剂法较细胞毒活性法方便快捷,灵敏度高,是一种极具潜力的高通量筛选抗肿瘤活性物质的模型。     

2-Aminobenzothiazoles Inhibit Virulence Gene Expression and Block Polymyxin Resistance in Salmonella enterica

One promising strategy to combat antibiotic-resistant bacteria is to develop compounds that block bacterial defenses against antibacterial conditions produced by the innate immune system. Salmonella enterica, which causes food-borne gastroenteritis and typhoid fever, requires histidine kinases (HKs) to resist innate immune defenses such as cationic antimicrobial peptides (CAMPs). Herein, we report that 2-aminobenzothiazoles block histidine kinase-dependent phenotypes in Salmonella enterica serotype Typhimurium. We found that 2-aminobenzothiazoles inhibited growth under low Mg²⁺, a stressful condition that requires histidine kinase-mediated responses, and decreased expression of the virulence genes pagC and pagK. Furthermore, we discovered that 2-aminobenzothiazoles weaken Salmonella’s resistance to polymyxin B and polymyxin E, which are last-line antibiotics and models for host defense CAMPs. These findings raise the possibilities that 2-aminobenzothiazoles can block HK-mediated bacterial defenses and can be used in combination with polymyxins to treat infections caused by Salmonella.     

Two Methods,One Goal: Structural Differences between Cocrystallization and Crystal Soaking to Discover Ligand Binding Poses

In lead optimization, protein crystallography is an indispensable tool to analyze drug binding. Binding modes and non-covalent interaction inventories are essential to design follow-up synthesis candidates. Two protocols are commonly applied to produce protein–ligand complexes: cocrystallization and soaking. Because of its time and cost effectiveness, soaking is the more popular method. Taking eight ligand hinge binders of protein kinase A, we demonstrate that cocrystallization is superior. Particularly for flexible proteins, such as kinases, and larger ligands cocrystallization captures more reliable the correct binding pose and induced protein adaptations. The geometrical discrepancies between soaking and cocrystallization appear smaller for fragment-sized ligands. For larger flexible ligands that trigger conformational changes of the protein, soaking can be misleading and underestimates the number of possible polar interactions due to inadequate, highly impaired positions of protein amino-acid side and main chain atoms. Thus, if applicable cocrystallization should be the gold standard to study protein–ligand complexes.     

Additive-Free Enzymatic Phosphorylation and Ligation of Artificial Oligonucleotides with C-Nucleosides at the Reaction Points

We report enzymatic phosphorylation and additive-free ligation of DNAs containing unnatural C-nucleotide residues through the action of T4 polynucleotide kinase and T4 DNA ligase. The artificial units are each made up of an alkynyl deoxyribose component and one of the unnatural nucleobases D * , T * , G * , and C * , corresponding—from a viewpoint of hydrogen-bonding patterns—to natural A, T, G, and C, respectively. Phosphorylation progressed quantitatively at the 5′-end in the cases of all of the artificial units in the chimeric DNAs. Ligation also smoothly progressed at the 5′-end in the cases of the D* and G* nucleotide residues, but only negligibly in those of their T* and C* counterparts. Chemical redesign of the last two units successfully improved the ligation efficiency, so that enzymatic ligation worked well for all of the artificial units in every 3′-natural ⋅ 5′-artificial, 3′-artificial ⋅ 5′-natural, and 3′-artificial ⋅ 5′-artificial terminal combination at the nicks.     

Synthesis and Evaluation of the Anticancer and Trypanocidal Activities of Boronic Tyrphostins

Molecules containing an (cyanovinyl)arene moiety are known as tyrphostins because of their ability to inhibit proteins from the tyrosine kinase family, an interesting target for the development of anticancer and trypanocidal drugs. In the present work, (E)‐(cyanovinyl)benzeneboronic acids were synthesized by Knoevenagel condensations without the use of any catalysts in water through a simple protocol that completely avoided the use of organic solvents in the synthesis and workup process. The in vitro anticancer and trypanocidal activities of the synthesized boronic acids were also evaluated, and it was discovered that the introduction of the boronic acid functionality improved the activity of the boronic tyrphostins. In silico target fishing with the use of a chemogenomic approach suggested that tyrosine‐phosphorylation‐regulated kinase 1a (DYRK1A) was a potential target for some of the designed compounds.     

Different Enzymatic Processing of γ‐Phosphoramidate and γ‐Phosphoester‐Modified ATP Analogues

Monitoring the activity of ATP‐consuming enzymes provides the basis for elucidating their modes of action and regulation. Although a number of ATP analogues have been developed for this, their scope is restricted because of the limited acceptance by respective enzymes. In order to clarify which kind of phosphate‐modified ATP analogues are accepted by the α‐β‐phosphoanhydride‐cleaving ubiquitin‐activating enzyme 1 (UBA1) and the β‐γ‐phosphoanhydride‐cleaving focal adhesion kinase (FAK), we tested phosphoramidate‐ and phosphoester‐modified ATP analogues. UBA1 and FAK were able to convert phosphoramidate‐modified ATP analogues, even with a bulky modification like biotin. In contrast, a phosphoester‐modified analogue was poorly accepted. These results demonstrate that minor variations in the design of ATP analogues for monitoring ATP utilization have a significant impact on enzymatic acceptance.