DALI - A quasi-Laue diffractometer for large proteins

To extend the capabilities and capacity for neutron macromolecular crystallography at the ILL, a second quasi-Laue diffractometer DALI has been commissioned at H141 as part of the ILL Endurance Programme. DALI utilizes a neutron velocity selector to provide higher transmission and a narrower bandwidth (δλ/λ ~10%) than LADI-III, both required to extend capabilities to the study of larger proteins.

DALI allows high-resolution (2.5 Å or better) studies of large proteins (>70kDa), in order to locate hydrogen/deuterium (H/D) atoms and protons/deuterons (H⁺/D⁺) of special interest, revealing important information on protonation, H-bonding and hydration. Neutron macromolecular crystallography is unique in its ability to provide these invaluable details at room-temperature, and without radiation damage.

Applications

Neutron macromolecular crystallography projects typically aim to address questions concerning:

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

Instrument layout

DALI 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.