Hi everyone,
I have a dimmer protein diffract to 1.6 A resolution.
After processing the data, the Linear R-fac was 0.26/0.038 (last/all), the
data quality seems good.
This data can be processed to P3 or P321 with the R-fac almost the same
After that, I used Bales to do the MR, two solutions were found in P32
(dimmer) and one in P32 21 (monomer)
Then, I refine the structure using phenix.refine in both P32 and P32 21
sets, but the R/Rfree stopped at 0.19/0.25 and never goes down.
Rfree 25% seems a little bit too high for a 1.6 resolution data.
However, if I treat the P32 data as a twin (with twin law h,-h-k,-l ), the
R/Rfree can down to 0.12/0.18.
I use P3 to run the phenix.xtriage (see bellows), it looks like the L-test
says it is not a twin data.
So, I am wondering is it a twin data or not?
The results are as follow.
"Twinning and intensity statistics summary (acentric data):
---------------------------------------------------------------------------
Statistics independent of twin laws
- /<I>^2 : 2.105
- <F>^2/ : 0.773
- <|E^2-1|> : 0.757
- <|L|>, : 0.508, 0.344
Multivariate Z score L-test: 2.013
Statistics depending on twin laws
------------------------------------------------------------------
| Operator | type | R obs. | Britton alpha | H alpha | ML alpha |
------------------------------------------------------------------
| -h,-k,l | M | 0.484 | -0.003 | 0.022 | 0.022 |
| h,-h-k,-l | M | 0.026 | 0.454 | 0.479 | 0.478 |
| -k,-h,-l | M | 0.507 | -0.004 | 0.026 | 0.022 |
------------------------------------------------------------------
Patterson analyses
- Largest peak height : 8.386
(corresponding p value : 0.29163)
The largest off-origin peak in the Patterson function is 8.39% of the
height of the origin peak. No significant pseudotranslation is detected.
The results of the L-test indicate that the intensity statistics
behave as expected. No twinning is suspected.
Even though no twinning is suspected, it might be worthwhile carrying out
a refinement using a dedicated twin target anyway, as twinned structures
with
low twin fractions are difficult to distinguish from non-twinned structures.
The correlation between the intensities related by the twin law h,-h-k,-l
with an
estimated twin fraction of 0.45 %
is most likely due to an NCS axis parallel to the twin axis. This can be
verified by
supplying calculated data as well."
Thanks!
Lauren
