Deer Peer,
i've got recently two proteins/crystals with the the following
phenomenon: One strand is swapped and extends into the sheet of its
symmetry mate. This happens obviously around a 2-fold axis and it was
hard to see at higher Rfrees. In both cases, only the first 10-20 amino
acids were swapped but I can imagine large parts could do the same,
albeit less likely.
Not sure if it applies here but I guess you can have a look on the
orientations in your lower symmetry experiments.
Best,
Matthias
On 26.08.2021 11:54, Peer Mittl wrote:
Der CCP4 community,
Is there a refinement program that can handle protein monomers sitting
on crystallographic 2-folds?
This is probably a strange question but we have the following
situation. We have a 2.6 Ang datasets in SG P3221 (Rpim=4%, Isa=19.6)
and a clear molrep solution with 2 chains, albeit with tNCS (0/0/0.5)
that can be refined to around 27/33% Rfactor. According to Vm a third
chain could be present. So far so good, but there is clear difference
ED for a third chain sitting exactly on the 2-fold. Since the protein
has a peculiar shape, one can tell even its orientation. I can relax
the symmetry to P32 (or even P1) and place the missing chain with 50%
occupancy on the 2-fold. This model can be refined, but I do not like
this work around, because the data is clearly P3221.
Any hints on similar crystal pathologies and how they have been
handled would be helpful.
All the best,
Peer
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Matthias Uthoff, PhD Student
Institute for Biochemistry
University of Cologne
Zülpicher Str. 47
D-50674 Cologne
Phone: +49 221 470 3211
E-Mail: [email protected]
Internet: http://px.uni-koeln.de
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