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
