BM29: bio-SAXS beamline

SYNOPSIS

BM29 is a tunable energy beamline (from 7 to 15 keV) for Small Angle X-ray Scattering (SAXS) experiments of biological macromolecule solutions with the goal to determine their 3-dimensional structures in a natural state with a 'low' resolution (~ nm).

At the beamline are essentially studied proteins, but also nucleic acids (DNA, RNA, peptides,...), protein-based complexes, lipids, membrane proteins (and surfactants), synthetic polymers, glycoproteins, viruses, etc.

The beamline has been re-built from EXAFS to bio-SAXS beamline and new Optics hutch equipment have been commissioned.

In December 2011 the bio-SAXS experiments stopped at ID14-3 and the set-up will be moved to BM29 location.  The beamline will be available for users from June 2012.

This high performance beamline has been designed to be easy to setup and user-friendly for providing a relative autonomy of users, to achieve:

• a routine data collection on protein solutions in the temperature range from 4 to 60° C
• sample handing equipment with off-axis visualisation, sample cell is a 1.8 mm diameter quartz capillary with a few tens of micron wall thickness
• automated data collection and processing pipeline using automated sample changer of a storage capacity up to three 96 well microplates (288 samples)

Continuous progresses have substantially improved the SAXS data quality (in resolution and reliability) making this beamline indispensable and complementary to other structural biology beamlines at the ESRF

APPLYING for BioSAXS BEAM-TIME

Application for beam-time will follow a rapid access model and can be made at ANY time. Those who wish to apply (excluding members of ESRF MX BAG Groups) should use the mechanism for:

MXnon-BAGproposal

In which it must be clearly indicated in the title of the proposal that the application is for BioSAXS beamtime on BM29.

SCIENTIFIC APPLICATIONS

The SAXS is a unique method for studying low resolution structure and structural transitions of individual proteins and large macromolecular complexes in solution. The presence of a biologically-oriented SAXS beamline at the ESRF will enable determination of low resolution shapes of proteins, which cannot be crystallised (or of those, which have been crystallised, in which case the shapes can be used as masks for low resolution phasing) and validation of MX models in solution. The cutting-edge experiments performed on small sample volumes in parallel with MX applications will provide valuable complementary information on the structure of targets in solution. 

Using SAXS to model structures:

•  using known atomic resolution structure of individual domains: SAXS used to determine the relative orientation and placement of these domains in a complex (rigid body modeling)
•  direct comparison of crystallographic structures (theoretical solution scattering pattern can be calculated from the atomic coordinates) with SAXS data
•  ab-initio envelope reconstruction: three-dimensional envelope generated from the one-dimensional SAXS curve

Figure shows X-ray solution scattering curves computed from atomic models of 25 different proteins with molecular masses between 10 and 300 kDa.  

TECHNICAL DETAILS

The working energies of BM29 are between 7 to 15 keV. It is a bending magnet beamline, however an elevated flux at detector plane is achieved thanks to the double multilayer monochromator (energy band pass ~ 10^-2) and 4 mrad torodial mirror 1.1 m long. Experimental hutch is equipped with a marble table housing the modular-length flight tube, 2D detector  (Pilatus 1M) and a sample handing equipment (automated sample changer). The achievable q-range is 0.01 - 5 nm^-1, which corresponds to the biggest measurable Rg (radius of gyration) of the investigated particle of 20 nm. Data collection, processing and analysis are performed in an automated manner using dedicated beamline software BsxCuBE.

SAXS/SANS PLATFORM FOR STRUCTURAL BIOLOGY

 The establishment of this integrated platform allows to CISB members and associates as well as external users of the ESRF and ILL access to both the new experimental facility for SAXS at the ESRF and existing facilities for small angle neutron scattering (SANS) at the Institut Laue- Langevin (ILL).

For those ILL proposals which have signalled a wish for ESRF SAXS time and which are awarded beam time by the ILL colleges, they will receive the official decision from the ILL which will at the same time tell them to now go and fill in the ESRF BioSAXS Rolling application. The review by the respective ILL and ESRF colleges/committees will be co-ordinated, as well as scheduling of successful SANS and SAXS time.

First users using both facilities during one trip have performed their experiments in the autumn 2010 and several other groups profited of this opportunity since than.

SANS uses the dramatic difference in the interaction of neutrons with hydrogen atoms ¹H and deuterons ²H and allows contrast variation studies on 2 (and more) component systems (as ribosome, DNA-protein complexes, ...) and is comlementary to SAXS.

For further details see SAXS/SANS PSB platform web page