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Thanks very much for all the suggestions so far. While I am pursuing all the checks and balances for twinning here are the Wilson plots I forgot to attach before..I am not sure what is going on, especially in B ! best, Iain > > > On Oct 25 2007, Iain Kerr wrote: > >> Dear all, >> >> I find myself posed with a rather interesting if somewhat confusing >> problem. >> >> Two crystals grown from the same conditions, let's call them A and B.. >> >> A: >> >> Resolution 2.1A >> Spacegroup P4? >> Rmerge 0.137 (0.324) >> Mean((I)/sd(I)) 41.0 (17.8) >> Completeness 100 (100) >> Multiplicity 53.6 (56.3) >> >> 4/mmm is clear from indexing...systematic absences show a clear 4 >> fold screw-axis..Pointless gives the most likely as P4_1 22 (I'm not >> clear on how it distinguishes P4_1 22 and P4_3 22..) >> >> Molecular replacement in Phaser, checking all the possible >> spacegroups, gives two outstanding solutions >> >> LLG Z-score >> P4_3 22 1972 41 (1mol/asu) >> P4_3 3801 54 (2mols/asu, ASU too full warning !) >> >> Solutions in other spacegroups had negative LLGs and/or were rejected >> for poor packing...the P1 solutions have LLGs of around -22000 >> >> I rebuilt both solutions in ARP/wARP both giving Rfree ~32% and Rfac >> ~23%...rebuilding (most residues accounted for), adding ligands and >> water makes no difference. >> >> Different iterations of refinement/rebuilding eg. cutting resolution >> make no difference...the maps are really well defined and packing is >> very reasonable with no clashes in either spacegroup. >> >> B: >> >> Resolution 2.3A >> Spacegroup C222? >> Rmerge 0.187 (0.402) >> Mean((I)/sd(I)) 11.8 (4.8) >> Completeness 99.4 (98.8) >> Multiplicity 6.8 (6.6) >> >> Mosflm: >> >> 11 144 mC 255.61 64.32 63.97 90.0 90.3 76.1 C2 >> 10 7 oC 90.69 90.74 124.09 90.3 90.7 89.7 C222,C2221 >> 9 7 tP 63.97 64.32 124.09 90.7 90.3 90.0 >> P4,P41,P42,P43,P422,P4212,P4122,P41212,P4222,P42212,P4322,P43212 >> 8 5 oP 63.97 64.32 124.09 90.7 90.3 90.0 >> P222,P2221,P21212,P212121 >> 7 5 mP 63.97 124.09 64.32 90.7 90.0 90.3 P2,P21 >> 6 4 mC 90.69 90.74 124.09 89.7 90.7 90.3 C2 >> 5 4 mC 90.69 90.74 124.09 90.3 90.7 89.7 C2 >> 4 3 mP 64.32 63.97 124.09 90.3 90.7 90.0 P2,P21 >> 3 1 mP 64.32 63.97 124.09 90.3 90.7 90.0 P2,P21 >> 2 0 aP 63.97 64.32 124.09 89.3 89.7 90.0 P1 >> 1 0 aP 63.97 64.32 124.09 90.7 90.3 90.0 P1 >> >> This suggests pseudo-merohedral twinning to me...in C222/C222_1 ...a >> and b are almost equivalent, so the 4/mmm symmetry would be apparent ? >> >> The Rmerge in 422 (19.6%) is only slightly higher than C222/C222_1 >> ....systematic absences again suggest a 4 fold...the curves >> calculated from the cumulative intensity distribution suggest partial >> twinning (when inputting C222_1 into the 'old' server to calculate a >> twin fraction from the partial twin test it says there are no twin >> laws for that spacegroup...) >> _ >> The outstanding solutions in Phaser this time are: >> >> LLG Z-score >> P4_3 22 1317 35 (1mol/asu) >> C222_1 2237 46 (2mols/asu, ASU too full warning !) >> >> Rigid body refinement of the solutions give (C222_1 ) Rfree 43%, Rfac >> 42% and ( P4_3 22 ) Rfree 44%, Rfac 43%....I'm thinking this is high >> and the maps from Phaser although fitting the placed molecules have >> poor connectivity (high Rmerge anything to do with this ?) >> >> Going back to crystal A it turns out the same C222/C222_1 is found >> but lower down in the list amongst the other solutions... >> >> I have attached the Wilson plots for both crystals...A has a large >> spike at high resolution (which is why I cut the data to 2.4A to try >> and improve refinement, to no avail) and B looks horrid ! >> >> OK, I think that is all the information I have at the moment...have I >> completely missed the correct symmetry..the Rmerge does seem high.. >> >> I have not yet tried to detwin the data (if it truly is twinned) and >> perhaps that is impeding refinement ?? >> >> Any suggestions would be greatly appreciated. >> >> Thank you, >> Iain >> _ >> >> >> >