Re: [ccp4bb] twin fraction varies between crystals?

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

Previous message:
Subject: Re: Stop Refmac from refining B factors?
From: "Harry M {- dot -} Greenblatt" harry {- dot -} greenblatt {- at -} WEIZMANN {- dot -} AC {- dot -} IL
Date: 2007-04-18

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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

Subject: Re: twin fraction varies between crystals?
From: "Radisky, Evette S {- dot -} Ph {- dot -} D {- dot -} " Radisky {- dot -} Evette {- at -} MAYO {- dot -} EDU
Date: 2007-04-18

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

CCP4bb navigation

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

Previous message:
Subject: Re: Stop Refmac from refining B factors?
From: "Harry M {- dot -} Greenblatt" harry {- dot -} greenblatt {- at -} WEIZMANN {- dot -} AC {- dot -} IL
Date: 2007-04-18