1) Why do you think there is twinning? If you label a structure whose
true spacegroup is H32 as having SG H3, then some of the twinning
analyses report that this is consistent with perfect twinning..
I believe the graphs of the moments from TRUNCATE give a true indicator.
Ditto the latest SFCHECK in ccp4-6.0.2 does a good analysis and usually
gets it right
2) If there is twinning smetimes a smaller crystal shows less effect.
3) If you can solve it then it can be refined using SHELXL.
MR works for twiinned data usually..
Eleanor
Mark Mayer wrote:
Hi,
I'd greatly appreciate advice on how to proceed with trying to solve and refine a structure with
nearly perfect merohedral twinning - or is this impossible? The SG is H3; most likely nmol is asu
is 4 from Matthews coefficient - but not sure about this.
Here are the twinning stats from phenix xtriage
------------------------------------------------------------------
| Operator | type | R obs. | Britton alpha | H alpha | ML alpha |
------------------------------------------------------------------
| h,-h-k,-l | M | 0.038 | 0.452 | 0.468 | 0.478 |
------------------------------------------------------------------
The data is for a novel ligand complex for which we have previously solved structures with
different ligands in other space groups - the protein has two domains, and these may have moved
compared to other structures.
So what should I do? Try and solve by MR using detwinned structure factors? Can Refmac refine
the twin fraction, or should I refine against detwinned mtz file? Or ... should we look for additional
xtal forms, or try additives to see if we can reduce twinning?
Thanks !!!
