Abstract
Small-angle X-ray scattering (SAXS) is an established method for studying nanostructured systems and in particular biological macromolecules in solution. To obtain element-specific information about the sample, anomalous SAXS (ASAXS) exploits changes of the scattering properties of selected atoms when the energy of the incident X-rays is close to the binding energy of their electrons. While ASAXS is widely applied to condensed matter and inorganic systems, its use for biological macromolecules is challenging because of the weak anomalous effect. Biological objects are often only available in small quantities and are prone to radiation damage, which makes biological ASAXS measurements very challenging. The BioSAXS beamline P12 operated by the European Molecular Biology Laboratory (EMBL) at the PETRA III storage ring (DESY, Hamburg) is dedicated to studies of weakly scattering objects. Here, recent developments at P12 allowing for ASAXS measurements are presented. The beamline control, data acquisition and data reduction pipeline of the beamline were adapted to conduct ASAXS experiments. Modelling tools were developed to compute ASAXS patterns from atomic models, which can be used to analyze the data and to help designing appropriate data collection strategies. These developments are illustrated with ASAXS experiments on different model systems performed at the P12 beamline.
Highlights
Small-angle X-ray scattering (SAXS) is a powerful method to study macromolecular solutions
anomalous SAXS (ASAXS) on biological samples remains challenging due to multiple reasons: (i) these samples are largely composed of lightweight atoms without absorption edges in the hard X-ray regime, (ii) the SAXS signal is usually rather weak, the ASAXS signal even weaker, (iii) samples are often limited in quantity and (iv) are sensitive to radiation damage (Jeffries et al, 2015)
The ASAXS technique was established at the P12 BioSAXS beamline (EMBL, Hamburg) and made available in the frame of the user access program
Summary
Small-angle X-ray scattering (SAXS) is a powerful method to study macromolecular solutions. By collecting several SAXS patterns at different X-ray energies (wavelengths) close to the absorption edge, the differences in the scattering patterns arising from variations in the scattering factor of the resonant atom can be detected Analysis of these differences provides information on the distribution of atoms of interest. ASAXS on biological samples remains challenging due to multiple reasons: (i) these samples are largely composed of lightweight atoms without absorption edges in the hard X-ray regime, (ii) the SAXS signal is usually rather weak, the ASAXS signal even weaker, (iii) samples are often limited in quantity and (iv) are sensitive to radiation damage (Jeffries et al, 2015) These experimental limitations can explain the relatively few examples of biological ASAXS studies published over the last decades, while standard biological SAXS on macromolecules has been attracting a growing number of users (Schroer & Svergun, 2018). Its application is further illustrated with the experiments and analysis on several test samples containing different anomalously scattering atoms
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
