It's a very interesting crystallographic and likely biological problem.
These patterns--a series of peaks along the axes of the Chi=180 plot,
with the peaks corresponding to a great circle in polar (3D)
space--indicate 2 back-to-back rings. On each great circle (each line
of peaks on the Chi=180 plot) there are 16 distinct peaks, so you have
likely D16 molecular symmetry i.e. you have two 16-mers forming a
two-ring structure.
This indicates that ASU has megadalton complex inside:
- in P2221 where only one crystallographic 2-fold can be used as axis of
D16 assembly there will be likely 16 molecules in ASU.
- in tetragonal form, if this P42 21 2 or P4 21 2, two crystallographic
2-folds can coincide with 2-folds of D16 assembly so there will be 8
molecules in ASU. I would expect for such symmetry (two perpendicular
assemblies, each 32 sub-units, in the unit cell) to result in very high
solvent content e.g. 75-80%.
If in a tetragonal space group you get ~70-80% of solvent for 8
molecules in ASU, then there is a very high chance that the entire
assembly sits on two perpendicular 2-fold axes and 8 NCS operators are
determined by the orientation of these axes. One of the 2-folds will
have to coincide with 42 screw axis or 4-fold axis, while the second
2-fold is the diagonal along ab directions.
In both cases, the NCS operators will be represented by rotations along
diagonal 2-fold crystallographic axis by angles 0, 22.5, 45, 67.5, 90,
112.5, 135, 157.5. These axes will intersect at the origin of
crystallographic system in both space groups.
If you don't have such situation, your best bet is cryoEM. It should
work for such big assembly.
Zbyszek
On 2021-07-28 13:48, Jorg Stetefeld wrote:
Hi,
we are seeking advice interpreting the attached selfrotation patterns
in terms of defining the NCS symmetry and eventually NCS-masks for
proper averaging/DM.
We are working with a muliti-domain transmembrane receptor composed
of several Ig -and FN-domains. We collected data in P4x212 and in
P2221 (see attachments).
Thx in advance
js
__
[1] [2]
Jörg Stetefeld
https://stetefeldlab.ca/ [2]
Find a job you like- You never work a day in your life!
[1] [2]
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