Crystallographic fragment screening at FragMAX is a well-established process, but project success depends strongly on the quality and robustness of the crystal system. We therefore recommend that your system is well characterised and ready before applying. We are always happy to discuss feasibility in advance.
Reproducible crystallisation
Fragment screening requires several hundred droplets with crystals. It is essential that crystals can be grown reliably and reproducibly, ideally yielding at least 200 suitable drops without excessive plate setup. For example, if only 10% of the droplets in a plate contain crystals then that’s not great, but 40% or more is good enough.
Crystallisation format
FragMAX workflows are optimised for sitting-drop plates with drop volumes ranging from 200 nL to 800 nL. SWISSCI 3-lens and MRC 2-lens plates are ideal, but other formats may also work. Hanging drops and large 24-well plates are more challenging, but we can explore workarounds if necessary.
Temperature
We can work at 4 °C and 20 °C. Whenever possible, we assess whether mounting can be done at room temperature without compromising diffraction quality but if this is not possible (and sometimes it is not) then we soak and mount in a cold room.
Crystal appearance
Robust crystals larger than ~50 µm in at least one dimension are preferred. While we have successfully screened smaller and thinner crystals, handling and data quality are generally improved with larger, sturdier crystals.
Crystal packing
Uniform diffraction to better than ~2.8 Å is recommended, ideally below 2.0 Å, to facilitate confident ligand identification.
Solvent tolerance
Solvent tolerance is not an issue at FragMAX. All our fragments are supplied in DMSO and we would typically mix them directly with the corresponding soaking buffer. But if your crystals are sensitive, we can use solvent-free protocols. We have done this for several projects and it worked very well. However, we recommend testing DMSO tolerance in advance, as you would in your home laboratory.
Diffraction behaviour
Be aware of complications such as twinning, pseudo-symmetry, multiple crystal forms, or radiation sensitivity. None of this is a show stopper, but it is important to fully understand the crystal system before embarking on a screening campaign.
Multiple crystal forms
If multiple well-diffracting forms are available, consider screening more than one. Hit rates and binding modes can vary significantly between forms.
Finally…
We understand that science is rarely predictable. If your project does not fit neatly into the “standard” workflow, please get in touch – we are always happy to explore options.