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A partial solution can potentially lead you to an appropriate MR solution. With many protein chains in the ASU, there will be several "reasonable" possibilities by Matthews analysis. When I originally solved 2A8D, cell content analysis suggested 8 monomers per ASU, but it was clear after a few MR runs that was not going to work. Inspecting the packing of a partial solution with 4 monomers, which formed a nice, biological-looking tetramer, clearly suggested that another dimer would fit into the lattice just nicely. A search with 3 such dimers produced an excellent MR solution starting point for the final refinement. I used a similar procedure for 3UAO. The Matthews analysis suggested 10-12 chains per ASU, but it was clearly 8 based on packing of partial solutions. A 4-dimer search was immediately successful. Cheers, _______________________________________ Roger S. Rowlett Gordon & Dorothy Kline Professor Department of Chemistry Colgate University 13 Oak Drive Hamilton, NY 13346 tel: (315)-228-7245 ofc: (315)-228-7395 fax: (315)-228-7935 email: [log in to unmask] On 4/30/2012 5:20 PM, [log in to unmask] wrote: > Provided that you guess the number of copies and your guess is > reasonably close, my experience is that Phaser will do the job. But > you have to tell it how many copies you expect, or it will never make > sense of the data. When I did my structure with 6(?) copies some years > ago, I guessed a number that was close enough and then when I > inspected the electron density I could see that there were more copies > than I had told the software and all was fine after that. It was > surprising to see that good solutions were obvious from a packing > consideration, while inadequate solutions were obviously wrong. > > Mark > > > -----Original Message----- > From: Ke, Jiyuan <[log in to unmask]> > To: CCP4BB <[log in to unmask]> > Sent: Mon, Apr 30, 2012 2:28 pm > Subject: [ccp4bb] Suggestions for solving a structure with 8-10 copies > per asymmetric unit > > 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