Without seeing the raw data and watching the integration of frames, I
would be suspicious of an incorrect space group assignment with an
Rmerge > 0.10. Are image spots well-predicted by the integration program
(all spots have predictions, all predictions have spots)? Are the spots
well-resolved (no or few overlaps) at the camera distance used? The lack
of falloff of I/sig(I) with resolution bin also looks atypical.
Typically, you would see a larger spread between the overall I/sig(I)
and the I/sig(I) in the highest resolution bin (assuming you have
collected data out to the resolution limit of the crystal). And with
10-fold redundancy, I would expect the overall I/sig(I) to be much
higher, if your integration program factors redundancy into the I/sig(I)
calculation.
I see results similar to this doing automated processing of frames in
real time during collection when the program goes off the rails and
chooses the wrong space group.
Cheers,
_______________________________________
Roger S. Rowlett
Gordon & Dorothy Kline Professor
Department of Chemistry
Colgate University
13 Oak Drive
Hamilton, NY 13346
tel: (315)-228-7245
ofc: (315)-228-7395
fax: (315)-228-7935
email: rrowl...@colgate.edu
On 3/29/2013 9:19 AM, hamid khan wrote:
Dear CCP4BB Members,
I am interested in your expert comments/opinions about two values of a
protein crystal diffraction data. Basically I am new to this field and
do not have much idea about diffraction data interpretation and
crystallography software’s use.
1)What could be the possible reasons for a high *Rmerge value, *say
like *0.185*?
2)Value *6.2* for average *I/sigma(I)* for higher shell means that the
resolution of the diffraction data is much higher than actually
measured, what could be the possible reasons for this?
For your ease I would like to past the table here;
Values in parentheses are for the last resolution shell
Space group P2221
Unit-cell parameters (A°)
a 58.08
b 101.32
c 103.47
Molecules in ASU 1
Resolution range 38.63 - 2.50 (2.59 - 2.50)
Total number of reflections 228902
Number of unique reflections 21600
Completeness (%) 99.1 (98.0)
*Rmerge 0.185 * (0.373)
Reduced χ2 0.94 (1.01)
*Average I/σ(I) 9.8 (6.2)*
Thanks for the tips..,
Hamid Khan
