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[ccp4bb]: high resolution refinement

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I would like to pose one question concering refinement of
high-resolution structures. This topic has been discussed to some extend
at the beginning of this year, but I would like to go for sure and have
an additional question:

The situation:
I have refined a quite large structure (6 monomers of 50kDa each in the
asu) at 1.7AA to quite reasonable R-values (Rwork: 16%, Rfree: 19%). Now
I have measured a 1.295A data set of the same crystal. The unit cell
dimensions differ less than 1%. Because of the huge amount of data
(close to 700.000 independent hkls) refmac5 and ARP/wARP with refmac4
appear to be THE refinement-programs to use (also in terms of tolerable
time for refinement).

The questions:
Is it the reasonable way to start the refinement of the 1.295AA
structure right from the beginning with all the data I have and let
maximum likelihood find its way. Or is it better to use the "old
fashioned" way to extend the high resolution limit in small steps and
search water in each step?

Is the following refinement strategy reasonable (each step until Rfree
- refinement at 1.295AA without water starting from 1.7AA structure with
- adding water with ARP at 1.295AA
- refinement with anisotropic B-factors
- introduction of multiple conformations
- refinement of occupancies
- refinement with hydrogen contributions

Taking in account resolution and the amount of data: Where should the
R-values converge after proper refinement?

Thanks for any comments!


Jan Abendroth
Institut fuer Biochemie
Universitaet Koeln
Zuelpicher Strasse 47
D-50674 Koeln

Tel: +49-(0)221 470 6455 (Labor)
                    6445 (Buero)
Fax: +49-(0)221 470 5092