Biocomposite films prepared from ionic liquid solutions of chitosan and cellulose

Blends of chitosan and cellulose were successfully produced using 1-butyl-3-methylimidazolium acetate (BMIMAc) as solvent media. Films were prepared from the blends by manually spreading the solution on a flat surface and precipitating the polymers in a mixture of methanol and water. To prevent the shrinkage of films, most of the absorbed water was removed by freeze drying under vacuum. Films prepared from the polymeric solutions were investigated by means of FT-IR, TGA, X-ray diffraction and SEM measurements. The shifting of the bands corresponding to -NH and CO groups of chitosan (FT-IR), the absence of the diffraction peaks at 2θ = 10.7 and 14.9° (XRD), the increased E_a for thermal decomposition for all the polymeric blends (MTGA), and the presence of an apparent homogeneous structure with no phase separation of the two polymers (SEM) provide evidence for the miscibility between chitosan and cellulose in the solid state.     

Quantitative analysis of the self-assembly strategies of intermediate filaments from tetrameric vimentin

In vitro assembly of intermediate filaments from tetrameric vimentin consists of a very rapid phase of tetramers laterally associating into unit-length filaments and a slow phase of filament elongation. We focus in this paper on a systematic quantitative investigation of two molecular models for filament assembly, recently proposed in (Kirmse et al. J. Biol. Chem. 282, 52 (2007), 18563-18572), through mathematical modeling, model fitting, and model validation. We analyze the quantitative contribution of each filament elongation strategy: with tetramers, with unit-length filaments, with longer filaments, or combinations thereof. In each case, we discuss the numerical fitting of the model with respect to one set of data, and its separate validation with respect to a second, different set of data. We introduce a high-resolution model for vimentin filament self-assembly, able to capture the detailed dynamics of filaments of arbitrary length. This provides much more predictive power for the model, in comparison to previous models where only the mean length of all filaments in the solution could be analyzed. We show how kinetic observations on low-resolution models can be extrapolated to the high-resolution model and used for lowering its complexity.     

Evidence of multifractality from emerging European stock markets

We test for the presence of multifractality in the daily returns of the three most important stock market indices from Central and Eastern Europe, Czech PX, Hungarian BUX and Polish WIG using the Empirical Mode Decomposition based Multifractal Detrended Fluctuation Analysis. We found that the global Hurst coefficient varies with the q coefficient and that there is multifractality evidenced through the multifractal spectrum. The exercise is replicated for the sample around the high volatility period corresponding to the last global financial crisis. Although no direct link has been found between the crisis and the multifractal spectrum, the crisis was found to influence the overall shape as quantified through the norm of the multifractal spectrum.     

Mechanical Operation and Intersubunit Coordination of Ring-Shaped Molecular Motors: Insights from Single-Molecule Studies

Ring NTPases represent a large and diverse group of proteins that couple their nucleotide hydrolysis activity to a mechanical task involving force generation and some type of transport process in the cell. Because of their shape, these enzymes often operate as gates that separate distinct cellular compartments to control and regulate the passage of chemical species across them. In this manner, ions and small molecules are moved across membranes, biopolymer substrates are segregated between cells or moved into confined spaces, double-stranded nucleic acids are separated into single strands to provide access to the genetic information, and polypeptides are unfolded and processed for recycling. Here we review the recent advances in the characterization of these motors using single-molecule manipulation and detection approaches. We describe the various mechanisms by which ring motors convert chemical energy to mechanical force or torque and coordinate the activities of individual subunits that constitute the ring. We also examine how single-molecule studies have contributed to a better understanding of the structural elements involved in motor-substrate interaction, mechanochemical coupling, and intersubunit coordination. Finally, we discuss how these molecular motors tailor their operation—often through regulation by other cofactors—to suit their unique biological functions.     

HIV-1 protease variants from 100-fold drug resistant clinical isolates: expression,purification, and crystallization

High-resolution X-ray crystallographic structures of HIV-1 protease clinical variants complexed with licensed inhibitors are essential to understanding the fundamental cause of protease drug resistance. There is a need for structures of naturally evolved HIV-1 proteases from patients failing antiretroviral therapy. Here, we report the expression, purification, and crystallization of clinical isolates of HIV-1 protease that have been characterized to be more than 100 times less susceptible to US FDA approved protease inhibitors.     

The Xenopus spindle is as dense as the surrounding cytoplasm

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A new method for cell immobilization.

A new method for producing particles and membranes containing immobilized bacteria is presented. These immobilized bacteria display good stability over time making them well suited for use in a packed-bed reactor. Such a reactor is tested as a function of the different parameters of the system. The results are qualitatively similar to those obtained with purified enzyme reactors, but some discrepancies with the plug-flow model are noted. It is necessary to use a more sophisticated model in order to fit the experimental data.