[ccp4bb] refining low resolution structures

[Mario Milani]

After many warning messages, I think I have to clarify the meaning of  
my question. After careful refining, in a low resolution structure  
often many residues (mainly in loop regions) can still adopt  
different dihedral conformations which are equally compatible with a  
low resolution electron density map. Thus, during the final steps of  
the refinement, it could be useful to restrain the dihedrals of such  
residues using the theoretical informations contained in Ramachandran  
plot to support/complete the poor information displayed by the  
experimental electron density map.
If this approach is used during the final stages of refinement i  
think it could provide structures of better quality. In this context  
i think that the use of Ramachandran restrain would follow the basic  
principle: enhance the weight of prior knowledge (geometrical  
costrains/restains) when experimental data are scarce.

mario
Mario Milani, PhD
University of Milan
Dep. of Biomol. Science and Biotech.
Via Celoria 26, 20133 Milan, Italy
T. +39 0250314892-4
F. +39 0250314895
http://digilander.libero.it/mario.milani/
http://users.unimi.it/biolstru/Home.html