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However, evaluation of post-SAXS experiment radiation damage on proteins is rarely performed because the allowable doses are highly sample-dependent, and must be determined on a case-by-case basis.
SMALL ANGLE NEUTRON SCATTERING RESOLUTION CALCULATOR FREE
Irreversible X-ray induced damage, essentially due to free radical formation in the sample at synchrotron sources, are a current limitation of SAXS experiments and often increase the amount of material needed or require radiation protectant such as glycerol or cryo-cooling. For example, radiation-induced aggregation has been observed with SAXS data for lysozyme, but without any change in folding topology. SAXS data is sensitive to oligomerization or aggregation of biological samples. While the reconstruction of 3D models of proteins from solution scattering data is common, it is an ill-posed problem and typically requires additional constraints such as the maximal distance between two points in a sample D max. It gives ensemble reciprocal space information on the size and shape of macromolecules. SAXS applied to dilute solutions of proteins is a long established technique in structural biology. Īmong the different available techniques, small-angle X-ray scattering (SAXS) presents unique advantages. This recent development is known as integrative structural biology. In this frame, it is essential to combine information from a variety of physical and chemical origins thus providing a solid basis to understanding molecular function. The most recent step forward in structural biology for characterizing large molecular assemblies is the integration of several complementary techniques to reach the goal of determining structures at atomic level. These results show that radiation damage can appear in different forms and strongly support the need to check the effect of radiation damage at synchrotron sources using the presented protocol. Radiation damage on the globular enzyme leads to an apparent increase in molecular sizes whereas the effect on the long virus is a breakage into smaller pieces resulting in a decrease of the average long-axis radius. The protocol has been tested on two different molecular systems: a large globular tetremeric enzyme ( β-Amylase) and a rod-shape plant virus (tobacco mosaic virus). It requires the acquisition of images of irradiated samples at the single molecule level in a timely manner while using minimal amounts of protein. Resultsīy employing atomic force microscopy, another common technique to determine the shape of biological macromolecules when deposited on flat substrates, we present a protocol to evaluate and characterize consequences of radiation damage. A major challenge with high-energy X-ray beam on such macromolecules is the perturbation of sample due to radiation damage. Small-Angle X-ray scattering performed at synchrotron sources is often used to characterize the shape of biological macromolecules.
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Synchrotron radiation facilities are pillars of modern structural biology.