Hi David,

1. First, make sure it’s not a salt crystal. The salt crystal has low resolution points. It is normal that the diffraction resolution is low due to the poor quality of the crystal itself. The basic principle of crystal optimization in our lab is to improve the crystal by gradient optimization of precipitant concentration, salt concentration, pH value and crystallization temperature according to the initial screening conditions. And you can also try to remove the flexible region;

2. If the crystal growth is irregular, it may be necessary to optimize the conditions. Hampton’s Additive Screen has a lot of additives to try. If you can get a crystal with a different crystal shape, the diffraction may improve;

3. You can try to dehydrate the protein crystals. The internal structure is closer to the single crystal by treatment such as dehydration or annealing;

4. According to my experience, the nucleation rate of hanging drop method is slower than that of sitting drop method, but the crystals formed are larger and more regular, which is more conducive to diffraction, which may be related to the volume and pressure change of droplets.

Hope it helps!