Hi all, I've got a 2.1 angstrom structure that I am refining. The space group is P212121. The structure is a dimer which I am refining without NCS restraints. Each monomer has 333 residues and one ligand, there are 33 Ile residues in each monomer. The first couple of rounds of refinement I had no problems, but during the third round phenix started breaking the main chain at the peptide bond and the side chain between CA and CB on some of the Ile residues. Specifically there are two breaks in chain A and four breaks in chain B, with two additional residues in chain B breaking only the CA-CB bond. Only one of the breaks is between the same residue in both chains. I'll be boring and run through my refinement process. This is the first time I've used phenix for anything but AutoSol and it is very likely that I have messed something up. Feel free to correct anything else I've done wrong along the way. Round 1, I rigid body refined chain A and B independently, performed simulated annealing, and refined individual coordinates. In COOT I manually refined and removed some bad loops. A few of the Ile were deleted but none of the problem ones Round 2, I refined individual_sites and individual_adp and turned off simulated annealing. In COOT I rebuilt some of the loops and fitted the ligand into the density. I generated a .cif file in eLBOW. Round 3, I refined the same as round 2 except that I included the .cif file. This is when I got the peptide bond breaks for Ile residues. I figured it was a fluke, fixed the breaks in COOT and rebuilt a few more residues in the loops. I ran another round of refinement and the same breaks showed up in the pdb file. I double checked the .geo file to see if Real Space Refine had made the bond distances were too long, but all the input distances were within one or two hundredths of an angstrom from ideal. I considered it was maybe the ADP refinement as I was borderline pushing the number of parameters I was refining given the number of reflections I had. I turned off the individual_adp refinement and reran refine_003. No luck. I tried increasing the weight of the geometry restraints over the observed data. I did this by increasing target_weights.wxc_scale = 1.5. (I suspect that I got this wrong. As I understood the wxc_scale is the ratio of the geometry restraints to the observed data. Feel free to point and laugh as long as you also provide an explanation as to what this parameter really means and how I should have done it,please.) Still no luck. For future information none of the problem isoleucines were located near the ligand or near any of the loops I was rebuilding. I think that's everything. Any help would be appreciated, Thanks, Kat -- SIPPEL,KATHERINE H Ph. D. candidate McKenna Lab Department of Biochemistry and Molecular Biology College of Medicine University of Florida