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Dear Jiyuan have you run any data diagnostics on your dataset? Ccp4 offers quite some options (truncate, detwin etc), and xtriage from PHENIX is also very powerful. And how sure are you of your laue group symmetry and space group (pointless via ccp4 and xtriage via PHENIX can be very helpful)? Also, is your data strongly anisotropic? Furthermore, the presence of pseudotranslation may not be an unlikely scenario given your large unit cell and large number of copies in the asu. MolRep in ccp4 can deal well with that, and is worth trying anyway regardless of pseudotranslation issues. Also I could not help notice that your c axis is b+b/2. best regards Savvas On 30 Apr 2012, at 17:41, Ke, Jiyuan wrote: > Dear All, > > I have a question regarding solving a crystal structure by molecular replacement. It is a single protein with a molecular weight of 25.5 kDa. The cell dimension is rather big from the diffraction data ( 90.9 Å, 143.9 Å, 216.3Å, 90°, 90°, 90°). The possible space group is P212121. With such a big unit cell, we predicted that there are 8-10 molecules per asymmetric unit. We have a decent model with sequence similarity of 49%. I tried several times with Phaser search with the current model and had difficulty to find any clear solution. Has anyone seen such cases and any suggestions to solve the structure? Thanks! > > Jiyuan Ke, Ph.D. > Research Scientist > Van Andel Research Institute > 333 Bostwick Ave NE > Grand Rapids, MI 49503 >