[ccp4bb] Merohedral twinning

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CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

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Subject: convert2mtz...
From: Kevin Cowtan cowtan {- at -} YSBL {- dot -} YORK {- dot -} AC {- dot -} UK
Date: 2007-03-29

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Subject: Re: Merohedral twinning
From: Christopher Colbert Christopher {- dot -} Colbert {- at -} UTSOUTHWESTERN {- dot -} EDU
Date: 2007-03-29

Subject: Merohedral twinning
From: Mark Mayer mayerm {- at -} MAIL {- dot -} NIH {- dot -} GOV
Date: 2007-03-29

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 !!!

CCP4bb navigation

CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

Previous message:
Subject: convert2mtz...
From: Kevin Cowtan cowtan {- at -} YSBL {- dot -} YORK {- dot -} AC {- dot -} UK
Date: 2007-03-29

Next message:
Subject: Re: Merohedral twinning
From: Christopher Colbert Christopher {- dot -} Colbert {- at -} UTSOUTHWESTERN {- dot -} EDU
Date: 2007-03-29