Re: [ccp4bb]: Refmac vs. cns with NCS

["David J. Schuller" <djs63@cornell.edu>]

***  For details on how to be removed from this list visit the  ***
***          CCP4 home page http://www.ccp4.ac.uk         ***

On Mon, 21 Jan 2002 rams@poori.biochem.uiowa.edu wrote:

> REfmac Vs CNS.
> CNS, simulated annealing and
> water picking do an absoltely wonderful job with strict NCS.

i am not entirely satisfied with NCS under CNS.  you have a choice between 
strict NCS (constraints) or NCS restraints. if you want to switch from one 
to the other, you have to build a new coordinates file and then re-run 
generate.  this is a nuisance.  and in both cases, the NCS is 
constrained/restrained by the NCS matrix, which itself is not refined. to 
do that, you have to build the whole multimer and put it through rigid 
body fitting.  why not allow the NCS matrix to be refined with either/or 
constraints & restraints?

and to bring in a dark horse, SHELX has a different approach to NCS which 
makes a lot of sense to me. NCS restraints are applied not to the position 
as defined by the NCS matrix, but by extra restraints on torsional angles. 
this is particularly appropriate for structures with hinges or other 
localized differences between monomers.

cheers,
=======================================================================
"Now that I'm a cranky, constipated old man I can afford to say that
 the younger generation of scientists makes me sick to my stomach."
                                                  - C.M. Kornbluth
=======================================================================
                        David J. Schuller
                        modern man in a post-modern world
                        MacCHESS, Cornell University
                        djs63@cornell.edu