Not enough information but some suggestions.
Are you sure the data is OK? Any sign of twinning? That is suspicious
if you cant decide between P43 and P43212
(Run SFCHECK on the amplitudes and try to understand output! )
Or send it and I will provide commentary.
Eleanor
Yanming Zhang wrote:
Hi ,
Please help me on this structure:
Data 1.8A: cell 84.892 84.892 172.580 90 90 90 with tetrahedral index
Space group: P43212 or P43, Final refinement Rfree indicates P43 is
better so most likely P43(also the systematic absence indicate P43 is it)
Matthew coeffient indicates: P43 3mol/a.u(2.58,52%) 2mol/a.u(3.87, 68%)
MR: Both Molerep and Phaser find out 2mol/au initially. Refinement
reaches Rfree 30% , R 27% finally. WE think, comparing with 1.8
resolution, The R and Rfree are too high. Also considering the 1.8A
resolution, there should be 3 molecules in total. So we engaged into
the effort to find out the 3rd molecule.
Phased MR by MOLREP did find out the 3rd, so did Phaser(fix two, find
out the 3rd). Both solutions gave relatively poorer statistics but
packing is perfect. The 3rd molecule, solved by phased MR of MOLREP
and PHaser respectively, can not superpose showing slightly different
orientations, but position is similar. Refinement indicates PHased
MOLREP MR gives lower Rfree.
Using totally 3 molecule, When I restrain or constrain NCS during
refinement(used TLS),R free goes way up (R~30, Rfree > 36%). If I
refine without NCS,R factors slip right away to 27/30 but this strange
thing
happens: two copies of the original solution refines very well - low B
factors,very good looking map. The 3rd copy, however, B factors are
high and the map is bad, no good density match with the model.And the
3rd molecule did no help to Rfree or R.
Story ends with my questions:
1,It seems the 3rd copy non-exist or globally disordered, under this
circumstance, can I say 'because of the 3rd molecule is globally
disordered so Rfree and R stay high (2mol/a.u with Rfree 30% R 27%,
1.8A data)?
2,Anything I should worry about in the process finding out the 3rd?
3,Are there suggestions to further lower down Rfree (the reasonable
Rfree should be around 22%)?
THANKS
Yanming
