You mention that your Rsym is 0.6 - this seems outrageously high (except if the 0.6 is just for your outer resolution bin). If 0.6 is indeed the overall Rsym you have a basic problem of unit cell and space group assignment to reconsider. Check if your processing accounts for all spots and check the input beam position - if its wrong you may have mis-indexed by one (e.g. on l, corresponding to the longest axis of your unit cell - c)
Later on: if you have any sulphurs in the structure you might consider sulphur-SAD to complement your MR. Let the MR find your S positions and go from there. Poul On 12/07/2010, at 05.00, 孙庆祥 wrote: > Dear ccp4 experts, > > I'm a beginner and have a problem with the following structure solution. I > need great help from you experts. Thanks in advance! > > The dataset is 1.6A resolution and the spots looks ok, except some smear in > the higher resolution. Space group is P1(could be P2 or P21). Completness is > above 95% and mosaicity is less than 1. Rsym is 0.6. > > Cell parameters are: a=18.2320 b= 39.6330 c=77.5260 alpha=104.8230 > beta=90.0780 gamma=90.0400 > > The model is about 60 amino acids snake venom protein with 60% identity. > However, no solution with an initiall R less than 0.7 was obtained by Molrep, > Phaser, or Phenix . > > Using a molrep search result (R=0.75, mtz in P1, 2 moelcules in AU), with > Refmac5 twin refinement, we could refine the structure to 40% Rfree and > 38%Rwork. The density looks good (can see hole in rings structures) for all > residues and no continous unexplained density is observed. However, the R and > Rfree does not go down no matter what we try... > > We tested the twinning by CNS or the crystal twinning server > (http://nihserver.mbi.ucla.edu/Twinning/) and found no twinning present. > > I'm sure the sequence is correct. > > I've tried hard on this for quite some time. Really appreciate if you could > help. > > Thanks and regards, > > Jeremy > > >
