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Dear Veronica, with 1st, 2nd, 3rd map you mean the density for the same dataset after three consecutive cycles of building-refining or three different maps from three different crystals? If it's the first case, it could be fine, it may mean that at each cycle you improve the map so you see signal from the different ligand molecules. If it's the second case, well, it could be simply an artifact. Are the ligands proximal one to another or bind different sites on the protein? Best V. 2016-10-26 14:32 GMT+02:00 Veronica Fiorentino < [log in to unmask]>: > Hello all, > I just solved a NCS-tetrameric (biological assembly is just a dimer) > crystal structures with ligand soak (same plate - same conditions). No > density for ligand is observed in the first map. In the 2nd, I have 1 > ligand bound. In the 3rd, I have 2 ligands bound. Is there any reason for > this 'random' behaviour? > > In addition, I observed just one crystal out of 20 gave a different unit > cell. Pointless confirms to me > "Best Solution: space group C 2 2 2". REFMAC refinement shows R/Rfree ~ > 20/25 % > Cell from mtz : 216.5 345.8 145.2 90.0 90.0 90.0 > Space group from mtz: number - 21; name - C 2 2 2 > > All other datasets have: > Cell from mtz : 147.0 354.3 217.4 90.0 90.0 90.0 > Space group from mtz: number - 20; name - C 2 2 21 > > I tried re-processing/refining the C2221 dataset in C222 but R/Rfree stays > ~45%. Can I also consider the C2221 dataset as a 'different crystal form'? > > Am I safe? > > Thank you all, > Veronica > -- *Valentina Speranzini, PhD* European Molecular Biology Laboratory Grenoble Outstation 71, avenue des Martyrs, CS 90181 38042 Grenoble Cedex 9, France Web: http://www.embl.fr E-mail: [log in to unmask] Tel: +33 (0)4 76 20 7630