Hi Everyone,
I have a (2.5 - 2.3 Angstroms) data set the process as I4 or I222.
Aimless indicates twinning in both space groups and all the lower
symmetry space groups consistent with the reduced cell. Molecular
replacement works in I4 but not I222 etc. I can see new density for a
ligand we are interested in some of the 6 subunits so all seems
promising. I've refined in refmac without the twinning turned on in
order to avoid model bias and end up with an R-factor/R-free of
0.268/0.305. However, if I repeat the last round of refinement with
twinning turned on the R-factor drops but not the R-free (R/R-free
0.237/0.305). Remac reckons the twin fraction is 0.628/0.372.
My question is does the drop in R-factor but not R-free suggest I am
over-fitting the model by refining twinning?
Running the data and model through pdb redo suggest the data isn't twinned.
Thanks,
Alun
--
Dr Alun R. Coker
Senior Lecturer
Wolfson Institute for Biomedical Research
University College London
The Cruciform Building
London
WC1E 6BT
Tel: 020 7679 6703 Ext 46703
Web: www.ucl.ac.uk/pxmed
