Hi Nicola, Try TRIS ir bis-tris, Chers <div>Em qui, 18 18e jul 18e 2019 às 17:03, Nicola Evans</div><div><[email protected]> escreveu:</div> I have an unidentfied blob of density at a crystal contact region. I tried inputting a magnesium ion there, it was clearly incorrect but it improved the R-factors by 3, so I would really like to identify the correct molecule! Is there a tool to identify ligands in structures? I have tried the Phenix ligand identification tool to no avail (although it did find some nice horseshoe shaped PEG ions). I used glycerol and PEG400 as a cryo protectant, and identified a few glycerol and PEG molecules in other parts of the structure but not in this spot (well conditions: 0.2 M Magnesium chloride hexahydrate, 0.1 M BIS-TRIS pH 5.5, 25% PEG 3,350). As this is an the crystal contact region the molecule isn't likely to be biologically significant. The data have been solved to 1.9Å. I have attached a screenshot of the mysterious density. I would appreciate any suggestions!In addition, I am adding water molecules to this protein, and often there are what appear to be long chains. Are these likely to be long chains of ordered waters, or more PEG molecules? Thanks in advance for your help!Nicola
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