Elektronalyse

Ohne Zusammenfassung     

Structure-based computational database screening, in vitro assay, and NMR assessment of compounds that target TAR RNA

There has been little prior effort to discover new drugs on the basis of a unique RNA structure. Binding of the viral transactivator Tat to the 5' bulge of the transactivation response (TAR) element is necessary for HIV-1 replication, so TAR RNA is a superb target. A computational approach was developed to screen a large chemical library for binding to a three-dimensional RNA structure. Scoring function development, flexible ligand docking, and limited target flexibility were essential. From the ranked list of compounds predicted to bind TAR, 43 were assayed for inhibition of the Tat-TAR interaction via electrophoretic mobility shift assays. Eleven compounds (between 0.1 and 1 microM) inhibited the Tat-TAR interaction, and some inhibited Tat transactivation in cells. NMR spectra verified specific binding to the 5' bulge and no interaction with other regions of TAR.     

Preparation and characterization of prototypes for multi-modal separation media aimed for capture of negatively charged biomolecules at high salt conditions

Several prototypes of multi-modal ligands suitable for the capture of negatively charged proteins from high conductivity (28 mS/cm) mobile phases were coupled to Sepharose 6 Fast Flow. These new prototypes of multi-modal anion-exchangers were found by screening a diverse library of multi-modal ligands and selecting anion-exchangers resulting in elution of test proteins at high ionic strength. Candidates were then tested with respect to breakthrough capacity of BSA in a buffer adjusted to a high conductivity (20 mM Piperazine and 0.25 M NaCl, pH 6.0). The recovery of BSA was also tested with a salt step (from 0.25 to 2.0 M NaCl using 20 mM Piperazine as buffer, pH 6.0) or with a pH-step to pH 4.0. We have found that non-aromatic multi-modal anion-exchange ligands based on primary or secondary amines (or both) are optimal for the capture of proteins at high salt conditions. Furthermore, these new multi-modal anion-exchange ligands have been designed to take advantage not only of electrostatic but also hydrogen bond interactions. This has been accomplished through modification of the ligands by the introduction of hydroxyl groups in the proximity of the ionic group. Experimental evidence on the importance of the relative position of the hydroxyl groups on the ligand in order to improve the breakthrough capacity of BSA has been found. Compared to strong anion-exchangers such as Q Sepharose Fast Flow the new multi-modal weak anion-exchangers have breakthrough capacities of BSA at mobile phases of 28 mS/cm and pH 6.0 that are 20-30 times higher. The new multi-modal anion-exchangers can also be used at normal anion-exchange conditions and with either a salt step or a pH-step to acidic pH can accomplish the elution of proteins. In addition, the functional performance of the new anion-exchangers was found to be intact after treatment in 1.0 M sodium hydroxide solution for 1 week. A number of multi-modal anion-exchange ligands based on aromatic amines exhibiting high breakthrough capacity of BSA have been found. With these ligands recovery was often found to be low due to strong non-electrostatic interactions. However, for phenol derived anion-exchange media the recovery can be improved by desorption at high pH.     

Abstract,weighted, and multidimensional Adamjan-Arov-Krein theorems,and the singular numbers of Sarason commutants

The classical Adamjan-Arov-Krein (A-A-K) theorem relating the singular numbers of Hankel operators to best approximations of their symbols by rational functions is given an abstract version. This provides results for Hankel operators acting in weightedH ²(T; ), as well as inH ²(T ^d ), and an A-A-K type extension of Sarason's interpolation theorem. In particular, it is shown that all compact Hankel operators inH ²(T ^d ) are zero.Author partially supported by NSF grant DMS89-11717.     

Phosphopeptide enrichment with stable spatial coordination on a titanium dioxide coated glass slide

Recent advances in phosphoproteomics have established powerful tools to analyze phosphorylation events. However, their spatial localization is lost due to sample homogenization procedures prior to the analysis. Imaging mass spectrometry (IMS) has emerged as a method to visualize the spatial distribution of molecules in tissue samples, but its application is still limited to relatively abundant molecules. Due to low phosphorylation stoichiometry, direct detection and imaging of protein phosphorylation by MS has not been achieved yet. Therefore we have developed a novel phosphopeptide enrichment strategy as a potential tool for in situ affinity imaging MS (AIMS). A specific type of titanium dioxide (TiO₂)‐coated glass slides was designed and validated with casein tryptic digests for their ability to selectively retain phosphopeptides while maintaining their spatial coordination. Copyright © 2009 John Wiley & Sons, Ltd.     

Early stages of ZnS nanoparticle growth studied by in-situ stopped-flow UV absorption spectroscopy.

The early stages of ZnS nanoparticle growth from supersaturated solution are investigated in situ by stopped-flow UV absorption spectroscopy with a time resolution of 1.28 ms. A model for data analysis is suggested which makes it possible to study both the average particle radius and the concentration. The average radii lie in the sub-nanometer range. During the first 40 ms, growth is predominantly governed by ripening.     

Irreversible Adsorption of Serum Proteins onto Nanoparticles

When a material comes in contact with serum or plasma, proteins will immediately adsorb to its surface. The extent of serum protein adsorption as well as the composition of the protein corona is thought to be decisive for the biological fate. The understanding of the mechanism underlying the concurrent adsorption of multiple proteins and the exact ways by which the adsorbed proteins interact with the biological setting, is still rudimentary. For both cases, a correct estimate of the composition of the protein corona is the key for an improved understanding. The protein corona composition is typically analyzed indirectly through analysis of the supernatant after protein desorption. However, in most cases the particles are not analyzed afterward in order to ensure that all proteins indeed have desorbed. Here, the results related to the analysis of the amounts of proteins in the corona are reported, focusing on the desorbed as well as the fraction of proteins that do not desorb. Irreversible protein adsorption can be observed in some cases. The results show that, in addition of the analysis of the supernatant, analysis of the particles is of critical importance to fully characterize the protein corona formed on nanoparticles.     

Isospin mixing in 12C

We observe a yield to the 1⁺T = 1 level in ¹²C at 15.11 MeV in the isospin forbidden ¹²C(d, d') and ¹⁰B(α, d) reactions at about 1 % of the yield to the 1⁺T = 0 level at 12.71 MeV. Observed yields to the T = 12⁺ level at 16.11 MeV in both reactions at about half the yield to the 15.11 MeV level preclude attributing this observed isospin violation entirely to final state mixing. From the ratios of the spectroscopic factors for the 12.71 and 15.11 MeV levels in ¹²C and the ground state of ¹²B from the ¹³C(d, t) and ¹³C(d, ³He) reactions, we find a charge dependent matrix element between the 1⁺ states in ¹²C of 179 ± 75 keV.     

Ergodic automorphisms of the infinite torus are bernoulli

We show that ergodic algebraic automorphisms of the infinite torus are measure isomorphic to Bernoulli shifts. Using the same techniques, we also show that the existence of such an automorphism with finite entropy is equivalent to an open problem in algebraic number theory.