Fragment-based screening is now well-established as a powerful approach to early drug ("lead") discovery.
Before you visit Diamond to use the XChem Facility you should have a robust crystal system that is as compatible as possible with our pipeline, this will help to ensure your time in the lab and data collection is as smooth and efficient as possible.
Make sure to check out our article, which contains all our collective knowledge, tips and tricks:
Collins, P.M. et al. Achieving a Good Crystal System for Crystallographic X-ray Fragment Screening. Preprints 2018, 2018090383 (doi: 10.20944/preprints201809.0383.v1) (link)
Potential Cause: Are you using a different batch of protein to previous plates?
Possible Causes: Was your original crystallisation optimised for larger, hanging drop format?
Possible Causes: Your crystal system may be sensitive to DMSO.
As a last resort: If you need to do short soaks the Shifter has a Dip-Soak programe that makes this method easy to do and enables you to add the compound straight before harvesting to reduce damage to your crystal. We would prefer if you optimise your crystallisation conditions to be compatible with a longer soak in DMSO or EG but if this is the only way we can do it!
Possible Causes: Some proteins are like that...
Possible Causes: Crystallisation condition may contain a volatile solvent or high salt.
Possible cause: Are they salt crystals?
Possible causes: If they are protein crystals then your crystallisation condition remains meta-stable even after crystals have grown.
Optimise your condition to find a lower-saturation condition - try seeding!
Try adding reservoir solution to drops before transferring compounds.
See if using the Watershed helps, it may help with this but we can't guarantee it, details of the Watershed can be viewed in the XChem Pipeline subpage
Last resort: Characterise how few droplets you can have open at once, by seeing how quickly the showers of crystals form. Once we know, we can modify the soak/harvest workflow accordingly. It makes everything a lot more tedious, though, so please try optimisation first.
Possible Causes: It always grew like this.
Possible Causes: Some crystals are like that...
If they are large, chunky needles i.e. larger than our beam (60x50 um), then you should be ok
If they are thin needles try to get them to lie consistently across the centre of the loop during harvesting (tough!)
You may need to do assisted data collection: it requires you watching every crystal and fixing any mis-centring - it's a bit tedious but we rigged the software to make it very easy.
We're working with Mitegen to develop new needle-supporting loops.
We're always working on various ways to improve data collection for these very cases, some things may take a long time to impelment but it's the nature of these big projects and updates
Possible Cause: Is your crystallisation condition straight from a screen?
Corrective action: Do more optimisation
Possible Cause: How extensively have you tried optimisation?
Potential Cause: Crystals may age faster than you realise
Possible Causes: Your crystals may be growing as sub-microscopic clusters or stacks of plates.
Potential Cause: If the bond is not physiolopgically relevant then your protein may be sensitive to oxidation
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