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Dear CCP4 users, I am trying to capture small molecule bound to the protein. These small molecules are solubilised in 100% DMSO. And the biochemical and biophysical assays shows micromolar affinity (two or three digit) towards the protein. We have extensively tried soaking (max 15% DMSO), long period soaking, growing protein crystals in the well precoated with the ligand and cocrystallization (max 5% DMSO) experiments, but have not succeeded to get any density for the ligand. The molar ratio that was used in the biochemical experiment is ~ 1:1000 (protein:ligand) in order to observe any binding. [one of the experiment used was microscale thermophoresis]. In these experiments the protein is in nM and small molecule is in microM quantities. For crystallization we are able to reach a maximum of 1:90 (in cocrystallization). It is not possible to approach a higher molar ratio because of the limitations of DMSO. So is there a possibility that we can capture the ligand in the crystal? I have come across ligands that have been captured even though they had mM binding affinities. So can anyone please suggest possible ways I can try to capture the small molecule. Thank you Regards Kavya -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.