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| Dmitri Svergun - | |
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Small-angle X-ray scattering (SAXS) is an increasingly important
tool for the study of biological macromolecules. The method
allows one to study native particles, from individual proteins
to large macromolecular complexes, in solution under nearly
physiological conditions. SAXS not only provides low resolution
models of particle shapes but in many cases answers important
functional questions. Most of fundamental biological processes
depend on supramolecular assemblies and their changes over time.
SAXS experiments employing high brilliance synchrotron radiation
allow one to analyse structural changes in response to variations
in external conditions, protein-protein and protein-ligand
interactions, and to effectively study equilibrium and
non-equilibrium processes like assembly or folding. In the analysis
of complex systems, SAXS, together with cryo-EM, should provide the
framework in which the high resolution models (crystallography and
NMR) can meaningfully be fitted.
The recent resurgence in biological SAXS should be attributed to the
synergy of hardware and software development. New SAXS instruments
have been built on high brilliance synchrotron sources, and novel
data analysis methods have become available. This tremendously
improved resolution and reliability of models deduced from high
quality SAXS data and made solution scattering a useful complementary
tool to high resolution methods, also for high throughput studies.
Advanced methods to analyze SAXS data from macromolecular solutions
will be presented including: ab initio low resolution structure
analysis; rigid body refinement and addition of missing fragments
to high resolution models; combined use of X-ray and neutron
scattering in the study of macromolecular complexes. Practical
applications of the methods will be illustrated by recent examples.
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