Small-angle scattering (SAS) of X-rays and neutrons (SAXS/SANS) experiences a renaissance in the studies of macromolecular solutions allowing one to study the structure of native particles and complexes and to rapidly analyze structural changes in response to variations in external conditions [1]. The last decade saw a major progress both in data analysis methods and instrumentation. These developments significantly enhanced the quality of structural models provided by SAS and offered the possibilities to rapidly study structural transitions also to analyze complicated objects like flexible macromolecules. Large scale structural studies in molecular biology are now possible on high brilliance synchrotrons thanks to the automation of the experiment, data processing and analysis.

Given the limited information content in the scattering data, robust data analysis and modelling methods are of major importance for broad applications of solution SAS in biology. To reduce the ambiguity of interpretation, SAS is often combined with other structural methods like crystallography, NMR and electron microscopy, and also with computational, biophysical and biochemical techniques to build hybrid models. In classical applications, SAXS generally yields low resolution quaternary structure but, very importantly, the method can also help to analyze equilibrium mixtures and to visualize flexible portions of the structures, not seen by the high resolution methods.

In the present talk, modern methods for SAS data analysis will be reviewed and new developments in the ATSAS program package will be presented. In particular, bioinformatics-type approaches, which are becoming more and more important, will be considered. These include the use of advanced computer algorithms for model building and validation [2], extensive applications of homology modelling [3] and the growing utilization of databases [4]. The recent developments in SAS data analysis methods will be illustrated by examples of application to various macromolecular systems. The perspectives of the synergistic use of SAS for hybrid modelling utilizing complementary methods will be discussed.

1. Svergun, D. I., Koch, M. H. J., Timmins, P. A., and May, R. P. (2013) Small angle x-ray and neutron scattering from solutions of biological macromolecules, Oxford University Press. 358 pp.

2. Tuukkanen AT, Kleywegt GJ, Svergun DI. (2016) Resolution of ab initio shapes determined from small-angle scattering. IUCrJ. 3:440-447.

3. Kikhney AG, Panjkovich A, Sokolova AV, Svergun DI. (2016) DARA : a web server for rapid search of structural neighbours using solution small angle X-ray scattering data. Bioinformatics, 32 : 616-8.

4. Valentini E, Kikhney AG, Previtali G, Jeffries CM, Svergun DI. SASBDB, a repository for biological small-angle scattering data. (2015) Nucleic Acids Res., 43 : D357-63.

Contact : mader@ill.fr