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Apologies, I think I neglected to attach the wilson plots...I'll do so on Friday. best, Iain 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 > _ > > > ------------------------------------------------------------------------ > > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.5.503 / Virus Database: 269.15.8/1089 - Release Date: 10/23/2007 7:39 PM >