Dear Fulvio,
what did your L-Test with the unmerged (P1) data look like? In order to
use twin refinement you should be sure that the structure is twinned.
Did you try all possible subgroups of R3? Generally, a triplet can be
treated as any other pseudo-merohedral twin, given it really is a
triplet - meaning integration and scaling in the lower (real) space
group, MR and twin refinement.
What is the indication that MR worked? The random R value (meaning an
unsolved structure) goes down from 58.5 to 50% if your structure is
(pseudo-)merohedrally twinned, and you are not very much under this value.
Best wishes
Andrea.
Am 07.05.2013 14:47, schrieb Fulvio Saccoccia:
Dear ccp4 users,
I have a reflections file obtained from a crystal initially scaled
in H3. All the attempts to phase by Molecular Replacement were not
successful and I succeeded only in P1. Based on previously solved
structures from the same protein, I suspected that twinning affected
crystals; so I used Twin refinement in Refmac. The program gave
indication of 3 domains:
Twin operator: H, K, L : Fraction = 0.335
Twin operator: H, L, -H-K-L: Fraction = 0.332
Twin operator: H, -H-K-L, K: Fraction = 0.333
With P1 and twin refinement I obtained a reasonable initial value of
FOM (0.50) but R/Rfree still remain at very large values (0.46/0.49).
I am not sure about twinning and data handling in presence of 3 twin
domains and I will appreciate a lot if someone will suggest me how to
deal out with these data.
Thanks
Fulvio
--
Dr. Andrea Thorn
Department of Haematology, University of Cambridge
Cambridge Institute for Medical Research
Wellcome Trust/MRC Building
Hills Road
Cambridge CB2 0XY, U.K.
andrea.th...@web.de
http://shelx.uni-ac.gwdg.de/~athorn
Tel: + 44 1223 763234
