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Hello everyone, I am refining a 2.5 angstrom structure whose phase is solved by molecular replacement with a search probe determined by SAD with 3 angstrom resolution. While I am able to see densities of a bunch of water molecules and ligands in the MR solved structure, which means that the phase is correct, the Rfree gets stuck at ~27%. The crystal belongs to P3221 and has a twinning fraction of 19%, according to Xtriage. Currently I've been sticking to Phenix for refinement, and twin law (-h, -k, l) has been applied. I was wondering if the CCP4 community would have any suggestions of how to refine this twinned structure, such as softwares to use, tricky strategies to choose, etc. I really appreciate any recommendations you would come up with my situation! Thank you in advance! Best, Mengbin -- Mengbin Chen PhD Candidate Christianson Laboratory Department of Chemistry University of Pennsylvania 231 S. 34th Street, #323 Philadelphia, PA 19104 USA Phone: (215)898-2227 Email: [log in to unmask]