Small Angle Neutron Scattering for membrane protein specialists
Beside crystallography and cryoEM, structural biology also include low resolution (about 1 nm) techniques in solution named Small angle scattering (SAS). They can be applied to samples that are too flexible to crystallize, to macromolecular complexes or to conformational equilibrium. Their results can be analyzed ab initio or by fitting atomic model, and provide large-scale information complementary to high-resolution techniques to understand protein behavior in solution.
The probe used in SAS techniques can be an X-ray Beam (SAXS) or a Neutron beam (SANS). SAXS is very powerful for soluble protein but cannot distinguish between molecules of different nature, such as protein and detergent, while SANS can: using specific deuteration, the detergent can be made invisible to the neutron beam.
In consequence, SANS is adapted to the study of membrane protein in solution. This is known for decades, but until now, several technical constraints blocked the generalization of the technique: 1/Detergents adequately deuterated were difficult to obtain, 2/Neutron sources had insufficient flux, 3/Instrumental set up and sample environment were not adapted to biological samples.
These technical locks have now been open thanks to a new collaboration which includes:
- adequately deuterated detergents (from ANSTO national deuteration facility),
- a high-flux and low-background SANS instrument (D22 at ILL)
- coupled with a size-exclusion chromatography set up (SEC-SANS ).
- Ab initio and model-based analysis software adapted from the SAXS toolbox are also available.
With these new technical capabilities, building a new community of users is required. Many membrane protein specialists did not mind acquiring SANS expertise up to now, because this technique was useless for them. Therefore, to help building this community, a free trial session was launched and its promotion was conducted by FILL2030.