Dear Chimera developers, My apologies if this question has been asked before but I was not able to find an answer so far. I am dealing with PDB files that contain too many individual chains and as such need two-character chain IDs. Ideally I do not want to split the PDB-files (to be able and work with single-character chain IDs). In addition, the PDB-file also contains more than 100,000 atoms and thus uses alphanumeric atom numbers. It seems Chimera is not aware of the two-character chain IDs because selecting a certain chain in the GUI shows only single character chain IDs and it leads to the selection of the two distinct chains (e.g. chain AA and chain BA are both treated as chain A). Is there a workaround? I’ve also noticed that saving such a PDB-file in Chimera changes all ATOM records to HETATM - I don’t know if this is related to the double-character chain IDs or alphanumeric atom numbers but this causes problems downstream because it’s very difficult to change this back to ATOM records without also affecting true HETATM entries. Thank you for your help! Best regards, Albert -- Albert Weixlbaumer Centre for Integrative Biology Department of Integrated Structural Biology Institute of Genetics and Molecular and Cellular Biology IGBMC - UMR 7104 - U 1258 1, rue Laurent Fries BP 10142 67404 ILLKIRCH CEDEX FRANCE Phone: +33 3 6948 5103 Email: Albert.Weixlbaumer@igbmc.fr<mailto:Albert.Weixlbaumer@igbmc.fr> OpenPGP KeyID: 0x7F644168