Dear All,
I am trying to refine a 1.9 A structure that indexed with excellent statistics (XDS) into a primitive monoclinic cell with cell lengths a=81.33, b=90.11, c=113.25 and beta angle =102.15. Data analysis (Xtriage) indicated strong pseudo-symmetry with an off-origin peak (53% of origin peak) at fractional coordinates (0.07, 0.5, 0.19). The intensity statistics did not indicate twinning and Pointless picked P2(1) as the space group with a 94% probability. Molecular replacement (Phaser) gave a solution with 4 molecules in the asymmetric unit with appropriate packing of symmetry-related molecules and NCS-restrained refinements with TLS led to very good quality maps. However, the Rfree for the completed model has stalled at 28% (Rwork is at 24%). I could not solve the structure in P2. Data processed in P1 has almost the same dimensions as the monoclinic cell (a=81.37, b=90.14, c=113.29) and MR with Phaser located 8 molecules in the asymmetric unit. The data scaled in P1 also has translational pseudo-symmetry at (0.06, 0.5, 0.185). Intensity statistics do not indicate twinning but Xtriage detects the two-fold as a pseudo-merohedral twin (-h,k,-l) and suggests the likely point group is P2. Initial refinement indicates the Rfree will likely remain high for the structure in P1 as well (Rfree ~37% and Rwork at 34%). I would really appreciate advice regarding the stalled Rfree and finding the true space group. Many thanks, Renu --------------------------------------------- Renu Kadirvelraj Biochemistry and Molecular Biology 120, Green Street University of Georgia Athens, GA 30605 Tel: (706) 583 0303 r...@ccrc.uga.edu
