Hi Phenix BB, We discovered that a fragment had degraded in our crystallography condition and the product was observed bound in the resulting crystal structure. Unfortunately we have been unable to separate certain stereoisomers of this compound or its analogues, and so are looking to simultaneously model two of the isomers into the crystal structure. I have made a .cif file corresponding to each isomer and modelled them into my crystal structures with altloc tags A & B, however after refinement, the occupancy of the two adds up to more than 1 in some instances (ie. 0.51 and 0.53). I’ve never had this before when trying to model dual conformations of the stereoisomers. I tried to make the ligands the same residue number as discussed in a previous thread (http://www.phenix-online.org/pipermail/phenixbb/2011-March/016859.html), however neither coot or pymol will open the pdb file after refinement if I do this. Unfortunately I am unable to share the pdb file as we do not want to disclose the compound structure. Does anyone have any suggestions as to how to proceed? Thanks in advance, Andrew Andrew Thompson PhD Candidate Molecular and Cellular Biology School of Biological Sciences The University of Adelaide, Australia