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As an additional comment on the issue of spatially correlated disorder, SHELX (and possibly other programs) has an elegant way of handling bump generation between disordered atoms. SHELX will only generate a bump if two atoms are in van der Waals conflict AND their occupancies sum to 1.1 or greater. This is on top of an exclusion for atoms from different altloc (non-zero part) numbers, and has the attraction of enforcing a physically reasonable model in any event. This approach requires no information about the correlated group membership of the atoms, although as George Sheldrick pointed out, this can be handled using free variables in SHELX. I bring this up because several current validation programs do not take correlated disorder into account when generating clashes, and I wish that an occupancy check would be more widely implemented. Best regards, Mark Mark A. Wilson Associate Professor Department of Biochemistry/Redox Biology Center University of Nebraska N118 Beadle Center 1901 Vine Street Lincoln, NE 68588 (402) 472-3626 [log in to unmask] On 7/25/14 2:51 AM, "Thomas Lütteke" <[log in to unmask]> wrote: >Just a quick thought that might be a workaround solution within the PDB >format restrictions: In NMR structures there are often multiple >conformations stored in different MODEL sections - this should in >principle be possible for x-ray structures as well, shouldn't it? > >Of course this is a waste of space, as you have to duplicate all atoms >and not only the ones that are included in multiple conformations, and >not all features might be handled by validation tools, but with the >limitations of the current PDB format there are not many ways to encode >this anyway. > >Best regards, >Thomas