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[ccp4bb]: Space group / NCS problems
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Hello all,
I am having a strange problem in the interpretation of my space group.
The protein appears to have orthorhombic symmetry (a=57 b=91 c=111) with
systematic absences along the a and c axes (see below). There appears to
be no systematic absences along the b axis. However, attempts at solving
the structure by molecular replacement would not refine to Rfactors below
41% work (49% free). MAD data was then collected, and a similar pattern of
systematic absences were observed. However, no solution could be found
(the heavy atom positions that were found by Shelx and SOLVE had low FOM
values and produced uninterpretable density).
When processed in a monoclinic setting, the axes stay the same, and
beta=90.
When processing the data through CNS or Yeates twinning server, it appears
as if I have perfect twinning. However, there are no twin laws for a
monoclinic space group with axes a=57 b=91 c=111.
I ran GLRF (self rotation function) and it showed that there was 2 fold
rotation axes along a, b, and c.
I ran a native patterson map to check for translational NCS, and there was
a large peak present at .0075 0.5 0.0 39.2049 (see list below).
This suggests that there is translational symmetry along the b axis.
However, with its position half way along the b axis, I would expect to
see systematic absences correct?
My questions are as follows:
If there is translational NCS axis along the b direction at 0 0.5 0, why
do I not see systematic absences?
In a native patterson, you do not see crystallographic 21 axes right?
If I do not see crystallographic 21 axes in a native patterson, then it
suggests that I have 21 2 21 symmetry with translational symmetry along
the b axis that gives no systematic absences. This does not make sense to
me.
Why do I get twinning statistics, when twinning is not possible?
Thanks in advance for any suggestions,
Matt
_________________________________________________________________________
Systematic absence information:
h k l Intensity Sigma I/Sigma
0 3 0 36.7 2.6 14.2
0 5 0 34.3 3.0 11.3
0 7 0 9.7 3.2 3.0
0 9 0 -2.0 4.2 -0.5
0 11 0 9.1 5.6 1.6
0 13 0 2.2 7.2 0.3
0 15 0 -0.4 8.1 -0.1
0 17 0 10.0 9.9 1.0
0 19 0 16.8 10.4 1.6
0 21 0 2.2 10.6 0.2
0 23 0 -13.5 14.4 -0.9
3 0 0 0.1 0.7 0.1
5 0 0 23.3 2.2 10.4
7 0 0 0.8 2.2 0.4
9 0 0 3.9 3.0 1.3
11 0 0 -2.6 3.6 -0.7
13 0 0 2.8 4.8 0.6
15 0 0 0.2 5.2 0.0
17 0 0 6.0 5.6 1.1
19 0 0 -3.3 6.4 -0.5
21 0 0 -2.6 7.4 -0.4
23 0 0 8.8 8.5 1.0
25 0 0 28.0 9.4 3.0
27 0 0 7.3 8.9 0.8
29 0 0 -1.7 10.3 -0.2
31 0 0 -6.8 12.1 -0.6
33 0 0 -21.2 13.4 -1.6
35 0 0 -9.7 13.7 -0.7
37 0 0 28.5 14.3 2.0
39 0 0 16.7 14.8 1.1
41 0 0 7.9 15.7 0.5
43 0 0 1.7 16.3 0.1
45 0 0 14.7 18.3 0.8
_____________________________________________________________________
Native patterson information:
peak no. interpolated (x,y,z,height)
1 0.0075 0.5000 0.0000 39.2049
2 0.0000 0.0000 0.4408 11.3819
3 0.0717 0.0000 0.0000 8.2458
4 0.0000 0.1166 0.0000 7.8074
5 0.0000 0.0000 0.2576 7.3205
6 0.0000 0.3846 0.0000 6.6375
7 0.0000 0.0649 0.2092 6.4106
(truncated)