Dear Rex, if you need to fit only one ligand, and if this fit is the starting point for further model building, the quickest way to do it is to do a manual superposition. (calculate - model/fit/refine/ - rotate/translate zone). If you click twice on an atom of the phenyl ring, your ligand will rotate around this atom. You then first translate this atom on top of the corresponding atom of your ligand in place, and then rotate the ligand to get a perfect fit. Best, Herman
________________________________ From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf Of Rex Palmer Sent: Friday, September 03, 2010 1:44 PM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] superpositioning two ligands This is not really protein crystallography but we are trying to model build a ligand into a protein binding site. A similar ligand is already in place and we want to replace this by initially superimposing a phenyl ring which is common to both ligands. We understand that such superpositioning can be done with eg Quanta but do not have access to this program. Does anyone know of a downloadable program that we could use instead? Rex Palmer Birkbeck College, London