Re: [ccp4bb] Merohedral twinning

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

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Subject: Postdoc positions in Yokohama
From: Jeremy Tame jtame {- at -} TSURUMI {- dot -} YOKOHAMA-CU {- dot -} AC {- dot -} JP
Date: 2007-03-30

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From: Frank von Delft frank {- dot -} vondelft {- at -} SGC {- dot -} OX {- dot -} AC {- dot -} UK
Date: 2007-03-30

Subject: Re: Merohedral twinning
From: Eleanor Dodson ccp4 {- at -} YSBL {- dot -} YORK {- dot -} AC {- dot -} UK
Date: 2007-03-30

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 !!!
>
>
>
>

CCP4bb navigation

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

Previous message:
Subject: Postdoc positions in Yokohama
From: Jeremy Tame jtame {- at -} TSURUMI {- dot -} YOKOHAMA-CU {- dot -} AC {- dot -} JP
Date: 2007-03-30

Next message:
Subject: Re: Multiple nucleation
From: Frank von Delft frank {- dot -} vondelft {- at -} SGC {- dot -} OX {- dot -} AC {- dot -} UK
Date: 2007-03-30