Chturikagae saxs - xxxi moboile mms 3gp
Recent examples include the use of SAS as a simple test of structural integrity for a group of creatine kinase mutants (Forstner et al., 1997) and as a measure of stability for a group of streptococcal protein G mutants undergoing guanidinium chloride mediated denaturation (Smith et al., 1996).Chen and colleagues (Chen et al., 1996) have also used SAS data to identify a partially folded kinetic intermediate consisting of a molten globule domain and a disordered region that forms during the folding of lysozyme.
The practical parts of this guide are based on the Australian Synchrotron SAXS beamline. : Senior beamline scientist Nigel Kirby has created a comprehensive guide to the Australian Synchrotron SAXS beamline. Small angle scattering (SAS) is emerging as a powerful tool for the study of biomolecules and their complexes in solution (Wall et al., 2000).
SAXS is used for the determination of the structure of particle systems in terms of averaged particle sizes or shapes.
The materials can be solid or liquid and they can contain solid, liquid or gaseous domains (so-called particles) of the same or another material in any combination.
Thus measuring times with line-collimation SAXS instruments are much shorter compared to point-collimation and are in the range of minutes to hours.
(Small Angle X-ray Scattering/ Wide Angle X-ray Scattering)There are many other websites which discuss SAXS.
The advantage over crystallography is that the samples need not be crystalline, the measurement is non-destructive and NMR methods encounter problems with macromolecules of higher molecular mass ( 30000-40000).
However, owing to the random orientation of dissolved or partially ordered molecules there occurs spatial averaging which leads to a loss of information.
SAXS instruments can be divided into two main groups: point-collimation and line-collimation instruments: 1) point-collimation instruments have pinholes that shape the X-ray beam to a small circular or elliptical spot that illuminates the sample.
Thus the scattering is centro-symmetrically distributed around the primary X-ray beam and the scattering pattern in the detection plane consists of circles around the primary beam.
Rather, the power of SAS lies in the facile determination of the shape and dimensions of native, unfolded and complexed proteins and in the ability to follow changes in these parameters as they occur (Millett et al., 2002, Wall et al., 2000, Trewhella, 1997).
SAS can be used to investigate the shape of both ligand -bound and uncomplexed proteins in solution.
Owing to the small illuminated sample volume the scattered intensity is small and therefore the measurement time is in the order of hours or days.