Rfree in molecular replacement

anja rabijns Anja.Rabijns at farm.kuleuven.ac.be
Wed Jul 23 02:26:38 EST 1997


At the moment I am trying to solve the structure of a protein by molecular 
replacement. This protein is very similar to the search model I am using 
(only the first ten amino acids are missing). Both proteins crystallize in 
the C2 spacegroup, however, the cell parameters are slightly different.
The structure of the search model was solved to 1.8 A and for the unknown 
structure I only have a 75 % complete data set to 2.6 A.

Now, the problem is that when I try to refine the new structure in X-PLOR 
after having found an easy solution for the molecular replacement, I 
immediately get a large difference between Rwork and Rfree. Rwork goes to 
crazy values of about 14 % and Rfree is around 36 %.

My question is what can be the reason for this and how can I avoid this 

Any suggestions are welcome,
Thanks in advance,

Anja Rabijns

Laboratory for Analytical Chemistry and Medicinal Physicochemistry
E.  Van Evenstraat 4,
B-3000 Leuven
Tel: (+32)-16-32 34 21
Fax: (+32)-16-32 34 14
anja.rabijns at farm.kuleuven.ac.be

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