Dynamically Polarized Solid Target for Neutron Scattering

1. Josh Pierce, J.K. Zhao Oak Ridge National Laboratory Don Crabb University of Virginia Dynamically Polarized Solid Target for Neutron Scattering

2. Presentation_name The Spallation Neutron Source • Completed May 2006. • 1.4 MW, ~8x ISIS. the world’s recent leading pulsed spallation source. • The peak neutron flux will be ~20–100x ILL, the world’s leading neutron scattering facility. • SNS will be the new leading facility for neutron scattering. • Room for eventual 24 instruments spanning physics, chemistry, biology, & materials science

3. Presentation_name Instruments and Sciences at SNS

4. Presentation_name High-Flux Isotop Reactor (HFIR)‏

5. Presentation_name Neutron Scattering Sciences at ORNL d (Å) d (Å) Momentum Distributions Biological Structure Viruses Small Proteins Hydrogen Modes Itinerant Magnets Molecular Vibrations Crystal Fields Critical Phenomena Micelles Colloids Vesicles Lattice Vibrations Electron-Phonon Interactions Polymers and Metals Alloys Zeolites Magnetic Films and Domains Small Molecule Diffusion Membranes Molecular Reorientation Larger Objects Large Scale Motions Polymers and Biological Systems Crystal, Fiber, and Magnetic Structures Liquids and Glasses Tunneling Spectroscopy Slower Motions Ultracold Neutrons Fundamental Physics Q (Å-1) Q (Å-1) Dynamics Structure

6. Presentation_name Challenges in Biology • In post-genomics era, one of the main challenges in biology is From Gene to Structure and Function. • We know the basic principles of protein, RNA & DNA structure, the architectures of >20,000 proteins and of a few molecular machines. However, major challenges are still ahead. • Neutron scattering is a great tool for structural biology due to neutron’s sensitivity to hydrogen. • Polarization enhances neutron scattering’s ability greatly.

7. Presentation_name Polarized Neutron Scattering • Hydrogen is the most abundant element in living matter (~50%), as well as in many other soft materials. • Hydrogen incoherent scattering is one of the largest sources of background. • Polarized neutron scattering from hydrogenous material drastically increases the signal-to-noise ratio.

8. Presentation_name Polarized Neutron Protein Crystallography 6 [x 10 ] 30 25.82 25 Coherent Cross-seciton of a typical sized protein (~40kDa) 20 =0) [barn] q 15 (at 2 10.47 W /d s 10 d 0.85 5 0 -100% 0% 100% Proton Polarization • >10 fold increase in diffraction intensity. • >10 fold reduction in incoherent background. • Decrease data collection time. • Ability to study smaller crystals. • Reduce cost for sample generation by 1000 fold. • Allow better study of H/D exchange on protein surface and active sites. • Allow better studies on protein hydration. • Allow site-specific diffraction (combined with spin labeling).

9. Presentation_name Utilize Spin Diffusion • The size of the cluster ~ 15 Å in diameter. • ~ 100 hydrogen atoms in the cluster. • Use the ‘spin-cluster’ to spin label proteins.

10. Presentation_name Experiments with polarized targets 50S Ribosome structure Left: Crystal structure (Nissen et al 2000). 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. • Successfully demonstrated in solution scattering. • Solution Scattering is low in information content. • The future lies in high resolution studies.

11. Presentation_name Dynamically Polarized Sample at SNS • First stage: quick and portable (between neutron beam lines) setup. • 7T solenoid & 5T compensated magnet. • Using helium-4 cryostat. • Major components ready (Magnet, MW generators, NMR, helium pumping system). • Second stage: custom and optimized setup for specific instruments, such as neutron protein crystallography: • Samples are very small (<< 1x1x1 mm3 ). • Compact apparatus needed. • Frozen spin mode desired. • Other applications: polarization filter for <1A neutrons.

12. Presentation_name Davies et al, Biochemstry 34: 16210-16220 (2ENG.pdb) Asp121: red Asp10: yellow Case Study: EGV (ORNL-LDRD) • Endoglucanase V (EGV): What’s the catalytic mechanism. • An important cellulase that catalyzes one of the steps in the breakdown of cellulose, a process which is critical for the production of biofuels. • The active site of EGV resembles that of lysozyme, with Asp10 and Asp121 on each side of the groove. • Asp121 is proposed to be the proton donor in the catalytic core. • The pH-dependent protonation states of Asp121 is thought to correspond to the two conformers of Asp121.