Tracing nucleation pathways in protein aggregation by using small angle scattering methods

Heat and alcohol-induced nucleation pathways of the whey protein β-lactoglobulin were investigated using small angle neutron and X-ray scattering for structural characterization. Protein solutions at various concentrations were either heated stepwise to 80 °C or mixed with ethanol to 50% (v/v). Heating induces dissociation of the β-lactoglobulin dimer in neutral pH aqueous medium, leading to nucleation at about 75 °C of tetrameric, cylindrical clusters, as indicated by three dimensional rigid body and bead modelling performed to fit scattering curves. In contrast to heating, ethanol addition induces the formation of fairly compact, internally disordered sphere-like clusters composed of rod-like submolecular structural units. At higher concentrations these clusters show typical colloidal behaviour, exhibiting long-range repulsive interactions, as also confirmed by dynamic light scattering measurements. The results contrast the effect of different unfolding scenarios on preferred nucleation pathways in subsequent protein assembly processes in various solution environments

Alcohol induced structural and dynamic changes in beta lactoglobulin in aqueous solution A neutron scattering study

Structural and dynamic properties of beta lactoglobulin beta LG were revealed as a function of alcohol concentration in ethanol and trifluoroethanol TFE water mixtures with circular dichroism CD , small angle neutron scattering SANS and quasi elastic neutron scattering QENS . The CD spectra showed that an increase in TFE concentration promotes the formation of the amp; 946; sheet structure of beta LG. The SANS intensities were fitted using form factors for two attached spheres for the native and native like states of the protein. At higher alcohol concentrations, where aggregation takes place, a form factor modelling diffusion limited colloidal aggregation DLCA was employed. The QENS data were analyzed in terms of internal motions for all alcohol concentrations. While low concentrations of TFE 10 v v lead to an increase of the mean square amplitudes of vibrations lt; u2 gt; and a retention of a native like structure but not to an increase of the characteristic radius of proton diffusion processes a. Addition of 20 v v of TFE induces aggregation, going along with a further increase of lt; u2 gt;. Further increase of TFE concentration to 30 v v changes the nanoscale structure of the oligomeric nucleate, but induces no further significant changes in lt; u2 gt;. The present study underlines the necessity of methods sensitive to the dynamics of a system to obtain a complete picture of a molecular proces

Longitudinal study of children with passively acquired antitoxoplasma antibodies

A group of 20 children born to mothers, suspected of active toxoplasma infection during gestation, was analysed. Multispecialistic examinations carried out in children for the period of 2-3 years have shown that the specific antibodies were acquired transplacentally. This enabled to exclude an active infectious process in children

A new time of flight small angle scattering instrument at the Helmholtz Zentrum Berlin V16 VSANS

Small angle scattering methods have become routine techniques for the structural characterization of macromolecules and macromolecular assemblies like polymers, block copolymers or micelles in the spatial range from a few to hundreds of nanometres. Neutrons are valuable scattering probes, because they offer freedom with respect to scattering length density contrast and isotopic labelling of samples. In order to gain maximum benefit from the allotted experiment time, the instrumental setup must be optimized in terms of statistics of scattered intensity, resolution and accessible range in momentum transfer Q. The new small angle neutron scattering instrument V16 VSANS at the Helmholtz Zentrum in Berlin, Germany, augments neutron guide collimation and pinhole optics with time of flight data recording and flexible chopper configuration. Thus, the available Q range and the respective instrumental resolution in the intermediate and high momentum transfer regions can be adjusted and balanced to the individual experimental requirements. This renders V16 VSANS a flexible and versatile instrument for soft matter researc