A quasi-Laue diffractometer for macromolecular crystallography

The quasi-Laue diffractometer LADI-III is used for single crystal neutron diffraction studies at high resolution (1.5 – 2.5 Å) of biological macromolecules, such as proteins or nucleic acids, providing unique information regarding hydrogen that is complementary to X-ray crystallography. Locating the positions of hydrogen/deuterium (H/D) atoms and protons/deuterons (H⁺/D⁺) provides us with knowledge of the protonation states of key amino-acid residues, or of bound ligands or drugs, as well as the orientation of water molecules. These details allow a more complete understanding of a macromolecule’s specific function and behaviour. Neutron macromolecular crystallography is unique in its ability to provide these invaluable details at room-temperature, and without radiation damage.

Neutron macromolecular crystallography projects typically aim to address questions concerning:

• Enzyme mechanisms
• Small-molecule (e.g. drug, ligand) binding interactions
• Rational drug-design

LADI-III uses a large cylindrical area detector composed of neutron-sensitive image-plates, which completely surround the crystal and allows large numbers of reflections to be recorded simultaneously. Data are collected using quasi-Laue methods in order to provide a rapid survey of reciprocal space, while reducing the background on the detector compared to use of the full white beam.