Hi phenixbb, I am working on a homodimer. Each protein has an internal b-sheet with three b-strands, however the sheets swap their middle strands. So a sheet consists of one strand from molecule A surrounded by two strands from molecule B or vice versa. As I am at 3 A resolution, I would like to set secondary structure restraints including correct hydrogen bonding between the strands of the two molecules. My problem: There is only one protein in the ASU and the "other" molecule is in deed just a symmetry mate. Phenix is not able to automatically detect this and if I provide the restraints myself, phenix discards them as it is falsely assuming the b-sheet is intramolecularly (all on chain A) and hence the strands are 30ish A apart. What is the best way of refining this feature? Thanks in advance, Matthias -- Matthias Uthoff, PhD Student University of Cologne Institute for Biochemistry Zülpicher Straße 47 D-50674 Cologne Phone: +49 221 470 3211 E-Mail:[email protected] Internet:http://px.uni-koeln.de