1. Dynamically Polarized Solid Target for Neutron Scattering at the SNS PST 07 J.K. Zhao Neutron Scattering Sciences Division, Spallation Neutron Source Oak Ridge National Laboratory

2. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Post-Genomics – DNA, Proteins and Beyond From genes to structure to function Challenges in Biology We know the basic principles of Protein, RNA & DNA structure, the architectures of >>20,000 proteins and of a few molecular machines

3. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY FROM REDUCTIONISM TO AN INTEGRATED UNDERSTANING OF COMPLEX BIOLOGICAL SYSTEMS

4. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Integrated platforms for Structural Biology STRUCTURAL HIERARCHY TECHNIQUECHALLENGE / FUTURE Hydrogen atomsNeutron Crystallography+ Polarized Neutron X-ray Crystallography Deuteration, High resolution ProteinsX-ray crystallography NMR Structural genomics, membrane proteins Protein-ligandsX-ray & Neutron Crys+Polarized Neutron, NMR, Mass Spec Protein function, drug design. Complexes Protein/Protein Protein/Nucleic Acid Membranes X-ray crystallography Electron microscopy Small angle scattering Reflectometry+Polarized Neutron Large complexes, Flexible complexes, Membrane Associated Sub-cellularElectron tomography X-ray microscopy X-ray tomography Confocal microscopy Localisation in cells. Molecular dynamics in cells. Transient complexes Pathways/networks/ assembly Interaction parameters Modelling/physics Systems biology

5. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Polarized Neutron Scattering  Hydrogen is the most abundant element in living matter (~50%) as well as many other soft materials.  Hydrogen has very strong polarization dependent scattering cross-section.  Without polarization, the huge hydrogen incoherent cros-section(79.8 barns) puts a severe limit on experiments, which are almost always flux limited.  At polarization =1, the hydrogen coherent cross-section increases from 1.8 to 14.7 barns, while its incoherent signal drops to 0 – a huge signal-to- noise gain.  The difference in cross-section between polarization =+1 and -1 can be exploited to polarize shorter wavelength neutrons (<1A), which are difficult to polarize with other techniques.  Polarization on nuclei other than hydrogen can be exploited as well. (Neutron Polarization=1)

6. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Coherent and incoherent cross- sections of a typical sized protein >10 folds increase in diffraction intensity: Reduce hydrogen incoherent background Solvent studies H/D exchange on protein surface >10 folds increase in diffraction intensity: Reduce hydrogen incoherent background Solvent studies H/D exchange on protein surface Structure Factors Spin-independent Spin-dependent Cross-Term

7. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Experiments with polarized targets 50S Ribosome structure Left: Crystal structure (Nissen et al2000). Right: Low resolution neutron scattering with polarized target (Zhao et al 1992). The experiment was carried out at the 5MW reactor. Similar result was NOT possible without polarized neutrons even at the best research reactor(60MW). Past neutron scattering experiments with polarized target have been confirmed by crystallography and proven to be very powerful. There are many situations where crystallography is not yet possible. Polarized neutron can enhance neutron protein crystallography!

8. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Experiments with polarized targets Comparison of two proteins (L3 and L4) within the 50S Ribosome as studied by polarized neutrons (color) and crystallography (ribbons)

9. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY The Polarized Solid Target for Neutron Scattering Project at SNS  First Stage: Quick and portable (between neutron beam lines) setup.  Using existing, 5T compensated magnet.  Using helium-4 cryostat for simplicity.  Major Components (Magnet, Microwave generators & counters, rf-generator for NMR, helium pumping system) have been bought.  Second Stage: Custom and optimized setup for specific instruments, such as neutron protein crystallography:  Neutron protein crystallography is severely flux-limited.  Samples are very small (<< 1x1x1 mm 3 ).  Compact apparatus needed.  Frozen spin mode desired.  Other Applications: Polarization filter for <1A neutrons.

10. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Initial 4He Cooling power Calculations

11. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Increase diffraction intensity: Eliminate solvent contribution:  use D 2 O as solvent and P D = 0, F s contains only diffraction from protein. Better way to study H/D exchange on protein surface, protein hydration.  e.g. by comparing the structure of protein in H 2 O and D 2 O. Solving the phase problem? Reduce background:  incoherent scattering vanishes at p n P H = +1

12. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Polarized ‘Spin-Cluster’ The size of the cluster ~ 15 Å in diameter. There should be ~ 100 hydrogens in the cluster. Molecule with < 200 atoms should be solvable by direct methods. If a ‘spin-cluster’ is fixed on a protein (spin labelling), it may provide a second phase for neutron protein crystallography. AFP polarization reversal (in bulk) will add more contrast.

13. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY The Spallation Neutron Source SNS construction completed May 2006. At 1.4 MW it will be ~8x ISIS, the world’s leading pulsed spallation source. The peak neutron flux will be ~20–100x ILL, the world’s leading neutron scattering facility. SNS will be a leading facility for neutron scattering. Room for eventual 24 instruments spanning physics, chemistry, biology, & materials science

14. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Instruments and Sciences at SNS

15. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Example protein to study  Produces all the oxygen in the earths atmosphere  Mechanism of water splitting unclear water orientations and aa protonation states needed  Crystals very sensitive to X-ray damage  Neutron protein crystallography is key to address the issue.  Polarized neutron will greatly facilitate the neutron diffraction experiment Photosynthesis (Photosystem II) Courtesy of Leighton Coats