Ligand-Binding Cooperativity Effects in Polymer-Protein Conjugation

We present an electron paramagnetic resonance (EPR) spectroscopic characterization of structural and dynamic effects that stem from post-translational modifications of bovine serum albumin (BSA), an established model system for polymer–protein conjugation. Beyond the typical drug delivery and biocompatibility aspect of such systems, we illustrate the causes that alter internal dynamics and therefore functionality in terms of ligand-binding to the BSA protein core. Uptake of the paramagnetic fatty acid derivative 16-doxyl stearic acid by several BSA-based squaric acid macroinitiators and polymer–protein conjugates was studied by EPR spectroscopy, aided by dynamic light scattering (DLS) and zeta potential measurements. The conjugates were grafted from oligo(ethylene glycol) methyl ether methacrylate (OEGMA), forming an overall core–shell-like structure. It is found that ligand-binding and associated parameters such as binding affinity, cooperativity, and the number of binding sites of BSA change drastically with the extent of surface modification. In the course of processing BSA, the ligands also change their preference for individual binding sites, as observed from a comparative view of their spatial alignments in double electron electron resonance (DEER) experiments. The protein-attached polymers constitute a diffusion barrier that significantly hamper ligand uptake. Moreover, zeta potentials (ζ) decrease linearly with the degree of surface modification in protein macroinitiators and an effective dielectric constant can be estimated for the polymer layer in the conjugates. All this suggests that ligand uptake characteristics in BSA can be fine-tuned by the extent and nature of such post-translational modifications (PTMs). We show that EPR spectroscopy is suitable for quantifying these subtle PTM-based functional effects from self-assembly of substrate and ligand

The Molten Globule State of Maltose-Binding Protein: Structural and Thermodynamic Characterization by EPR Spectroscopy and Isothermal Titration Calorimetry

Employing site-directed spin labeling (SDSL), the structure of maltose-binding protein (MBP) had previously been studied in the native state by electron paramagnetic resonance (EPR) spectroscopy. Several spin-labeled double cysteine mutants were distributed all over the structure of this cysteine-free protein and revealed distance information between the nitroxide residues from double electron–electron resonance (DEER). The results were in good agreement with the known X-ray structure. We have now extended these studies to the molten globule (MG) state, a folding intermediate, which can be stabilized around pH 3 and that is characterized by secondary but hardly any tertiary structure. Instead of clearly defined distance features as found in the native state, several additional characteristics indicate that the MG structure of MBP contains different polypeptide chain and domain orientations. MBP is also known to bind its substrate maltose even in MG state although with lower affinity. Additionally, we have now created new mutants allowing for spin labeling at or near the active site. Our data confirm an already preformed ligand site structure in the MG explaining its substrate binding capability and thus most probably serving as a nucleation center for the final native structure

The change of consumption patterns in Germany – an evidence of the individualization of lifestyles or the effect of socio-demographic changes?

Following the results of different empirical studies the consumption patterns of German households changed significantly during the last decades. While this change was attributed to a dissolving correlation between lifestyle and social status for a long time, more and more studies focus on the relationship of lifestyle and socio-demographic criteria again. This report analyses the effects of social composition regarding age, income and households types on the use of income between 1978 and 2008. The results of the decomposition analysis reveal that the socio-demographic components cannot explain the change of consumption patterns in Germany. Rather it seems that different social conditions during socialisation affect lifestyles and should be considered when analysing consumption patterns