Crystals of trp repressor suitable for high-resolution neutron Laue diffraction studies

Crystallization and preliminary neutron-diffraction measurements of wild-type variant Val58→Ile of the Escherichia coli trp repressor are reported. A vapor-diffusion chamber suitable for initial protein-solution volumes in the range 0.2–0.5 ml was used to grow cube-shaped crystals with edge dimensions in the range 0.8–1.4 mm. Neutron Laue measurements to a nominal resolution of 2.1 Å were recorded from a D₂O-exchanged crystal using the LADI instrument at ILL. These results demonstrate that it will be possible for the first time to obtain a full-atom neutron structural model of a DNA-binding protein plus its associated solvent. Direct observation of hydrogen bonding between protein and solvent should enhance understanding of the role of solvent in protein–DNA recognition.