[ccp4bb]: High and low B-factors

[Ralf Bienert <bienert@mdc-berlin.de>]

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Hello everybody!

I solved a SAD structure to 1.8 A of a Se-Met protein and refine it with
refmac5.
However, I observed negative difference density around my Se-sites,
together with high B-factors of this atoms. I think this is due to
radiation damage. So far it is interpretable.
But why do I have so low B-values for my CE atoms, even lower than the
B-value of the other atoms of Se-Met.
My question now is how to interprete this observation and how to deal with
it. I just set the occupancy of both atoms to lower (same) values to get
rid of the negative difference density, but is this the right way???? Of
course, the B-value decresed, as well of CE.

To get an idea I list my "worst" data (occupancy=1, B-value):

 N   MSE                         1.00 45.98  N
 CA  MSE                         1.00 45.15  C
 CB  MSE                         1.00 43.74  C
 CG  MSE                         1.00 44.29  C
SE   MSE                         1.00 49.38 SE
 CE  MSE                         1.00 9.79   C
 C   MSE                         1.00 43.49  C
 O   MSE                         1.00 44.28  O

 N   MSE                         1.00 25.08  N
 CA  MSE                         1.00 25.90  C
 CB  MSE                         1.00 25.00  C
 CG  MSE                         1.00 29.97  C
SE   MSE                         1.00 35.56 SE
 CE  MSE                         1.00 19.57  C
 C   MSE                         1.00 24.97  C
 O   MSE                         1.00 23.98  O

Thanks in advance.
Ralf


*********************
Ralf Bienert
Crystallography Group
MDC-Berlin
*********************