[ccp4bb] High Rmerge and I/sigma values....?

[hamid khan]

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