Re: [ccp4bb] twin fraction varies between crystals?

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CCP4bb <-- 2007 <-- April 2007 <-- 18 April 2007

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Subject: SUMMARY: Getting started with twin refinement with SHELXL
From: "Radisky, Evette S {- dot -} Ph {- dot -} D {- dot -} " Radisky {- dot -} Evette {- at -} MAYO {- dot -} EDU
Date: 2007-04-18

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Subject: Re: Stop Refmac from refining B factors?
From: Eva Kirchner eva {- dot -} kirchner {- at -} UNI-TUEBINGEN {- dot -} DE
Date: 2007-04-18

Subject: Re: twin fraction varies between crystals?
From: Eleanor Dodson ccp4 {- at -} YSBL {- dot -} YORK {- dot -} AC {- dot -} UK
Date: 2007-04-18

This is not definitive, but in a similar case - P21 with a~c, we could
detect twinning from the moment plot in TRUNCATE with 15% of data.. (ie
run SCALA and TRUNCATE option - scales poorly determined, and I think we
fixed them to unity..)
Eleanor

That meant you could test the crystals at home and only take the likely
ones.

Radisky, Evette S. Ph.D. wrote:
> Can you (or anybody else) expand upon this -- what would be a
> recommended screening protocol for twinning? Collect X degrees of data,
> scale, merge, run mmtbx.xtriage? How many degrees of data will it take
> to give a reliable estimate, and does this depend upon crystal
> orientation, SG, merohedral vs pseudo-merohedral twinning, other
> parameters???
>
> We have a pseudo-merohedrally twinned crystal (SG=C2 with beta~90) and
> the twin fraction was ~0.44 in the two crystals we have tested, but we
> are now taking 40 new crystals to NSLS and I would welcome advice for
> how to screen efficiently. Thanks!
>
> Evette
>
> Evette S. Radisky, Ph.D.
> Assistant Professor and Associate Consultant II
> Mayo Clinic Cancer Center
> Griffin Cancer Research Building, Rm 310
> 4500 San Pablo Road
> Jacksonville, FL 32224
> (904) 953-6372 (office)
> (904) 953-2857 (lab)
>
> -----Original Message-----
> From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of
> Christopher Colbert
> Sent: Tuesday, April 17, 2007 4:01 PM
> To: CCP4BB@JISCMAIL.AC.UK
> Subject: Re: [ccp4bb] twin fraction varies between crystals?
>
> I experienced the same behavior. Crystals from the same drop could have
> varying twin fractions. Screening for twinning can be done with
> remarkably few degrees of data. Of course, all proteins and all twins
> aren't equal. So, don't expect to have varying twin fractions all the
> time.
>
> Happy Refining,
>
> Chris
>
> On Tue, 17 Apr 2007, Mark Mayer wrote:
>
>
>>>> For cases where people have had merohedral twinning, did the twin
>>>> fraction vary substantially between individual crystals grown under
>>>> indentical conditions? I have no prior experience with merohedral
>>>> twinning, and was surprised to see that the twin fraction varied
>>>>
> substantially as detailed below, and that by screening we were able to
> get untwinned xtals.
>
>>>> The project started with a weak home data set for which the twin
>>>> fraction was 0.478, and which scaled in both H3 and H32. We just came
>>>>
>
>
>>>> back from APS with data sets from another three crystals, for which
>>>> the ML twin fraction, estimated using phenix.xtriage with scalepack
>>>> merged intensities as input, varied from 0.335, 0.219 and 0.02. The
>>>>
> latter is refining very nicely, in H3 and will not scale in H32.
>
>>>> Thanks - Mark
>>>>
>>>>
>
> Christopher L. Colbert, Ph.D.
> Assistant Instructor Phone: (214) 645 5944
> University of Texas Southwestern Medical Center FAX: (214) 645 5945
> 6001 Forest Park Lane
> Dallas, TX 75390
>
>
>
>

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CCP4bb <-- 2007 <-- April 2007 <-- 18 April 2007

Next message:
Subject: Re: Stop Refmac from refining B factors?
From: Eva Kirchner eva {- dot -} kirchner {- at -} UNI-TUEBINGEN {- dot -} DE
Date: 2007-04-18