Frozen spin targets in ribosomal structure research

Area of Science:

• Structural Biology
• Biophysics
• Neutron Scattering

Background:

• Polarized neutron scattering is highly sensitive to nuclear spin polarization, especially proton spin polarization.
• A single proton in a deuterated environment provides scattering efficiency comparable to 10 electrons in X-ray anomalous diffraction.
• Controlling neutron and nuclear spin polarization is key for neutron scattering from nuclear spin labels.

Purpose of the Study:

• To determine the in situ structure of ribosomal RNA (rRNA) and total ribosomal protein (TP) in the large subunit of E. coli ribosomes.
• To utilize polarized neutron scattering with highly polarized proton and deuteron spin labels.
• To establish a foundation for future studies on ribosome-bound mRNA and tRNAs.

Main Methods:

• Production of pure deuteron and proton spin labels via Nuclear Magnetic Resonance (NMR) saturation.
• Orientation of nuclear spins using dynamic nuclear polarization in an external field.
• Measurement of polarized small-angle neutron scattering using frozen spin targets of deuterated E. coli ribosomes.

Main Results:

• Achieved proton spin polarizations exceeding 80% in ribosomes at temperatures below 0.5 K.
• Established a relaxation time of one month for the polarized target at 130 mK (frozen spin target).
• Determined the in situ structures of rRNA and TP, consistent with room temperature neutron scattering in H2O/D2O mixtures.

Conclusions:

• Highly polarized proton spin targets enable sensitive structural analysis of biological macromolecules.
• The frozen spin target approach provides a stable platform for neutron scattering experiments.
• This method is a prerequisite for future in situ structural determination of ribosome-bound nucleic acids and proteins.