A huge advance for high-resolution neutron crystallography of large proteins
In October ’25, a completely new neutron-sensitive cylindrical image plate detector has been built and installed in the DALI instrument at the ILL. This is a major upgrade that significantly improves the instrument performance. Built in the framework of the ILL upgrade programme Endurance (2016-2024), DALI is a quasi-Laue diffractometer designed for high-resolution studies of large proteins.
During the last 2025 reactor cycle, neutron diffraction tests and analyses were performed using crystals of proteins covering a wide range of molecular weights, from the very small (6 kDa) to the very large (271 kDa).*
The results of these tests show that the two neutron protein crystallography diffractometers, LADI-III and DALI are highly complementary; LADI-III providing higher quality diffraction data for small to medium sized proteins (5-70 kDa) and DALI, with its new detector and narrow bandwidth velocity selector, now providing diffraction data of higher quality for large proteins (70-150 kDa).
In addition, the tests show that DALI can even be used to study very large proteins (>150 kDa) that were previously out of range. This represents a step-change in capabilities for neutron protein crystallography research and further cements the ILL’s position as world-leading in the field.
“This has been a huge effort and great work by all involved - Un grand merci à Olivier Aguettaz, Benjamin Giroud, Lukas Gajdos, Juliette Devos, Théodore Arnaud [ILL] et Nicholas Croy [Uppsala University]!”, says Matthew Blakeley ILL scientist and Instrument Responsible for LADI-III and DALI.
16-hours exposure from a crystal of 105 kDa protein (LecA/PheGal complex, unit-cell, a=74, b=111, c=113 Å / P212121). Complete data set collected to 2.0 Å resolution.
[Protein Lectin LecA is a virulence factor of the pathogenic bacteria Pseudomonas aeruginosa. Specific ligands - molecules binding to specific sites of the protein to form molecular complexes – can counteract P. aeruginosa infections if they block specific protein sites involved in the process.]
14-hours test exposure from a crystal of 271 kDa rubisco (unit-cell, a=158, b=158, c=202 Å / C2221). Diffraction to 2.4 Å resolution. Full data set to be collected in 2026. Currently the largest protein published to high-resolution with neutron diffraction is the 125 kDa Inorganic pyrophosphatase using LADI-III.
[RuBisCO, involved in the first step of photosynthesis, is found in plants and other photosiynthetic organisms and is the most abundant protein on Earth.]
DALI is the second quasi-Laue diffractometer at ILL (with LADI-III) used for single-crystal neutron diffraction studies of biological macromolecules at high resolution (1.5 - 2.5Å), allowing the visualisation of key hydrogen or deuterium atoms within biological macromolecules. These instruments use 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.
Protein crystallography is crucial in biomedical research and drug development. It helps scientists understand the 3D structure of proteins and their functions, revealing how proteins interact. The procedure involves crystallising proteins into ordered lattices and analysing the resulting diffraction patterns from X-rays or neutrons. Neutron crystallography offers better resolution whenever hydrogen atoms are concerned.
(*) The size of a protein is measured by the number of amino acids it contains or by its total molecular mass, which is normally reported in dalton (Da).
ILL instrument: DALI
ILL contact person: Matthew Blakeley