Jan Abendroth a écrit :
Hi all,
kind of a weird problem - the R-factors of a refinement using the new
twin refinement in refmac are low, almost suspiciously low:
A good 1.9AA data set, space group H3/R3, many statistics starting
with truncate's cumulative intensity distribution clearly suggest
twinning. The structure (SSGCID target) was solved by MR, very rigid
beta-helix (see 3bxy, very cool fold!), maps nice. I use refmac
5.5.0046 for refinement, with and without the new TWIN flag.
Here my concerns:
Despite 0.3/0.7 twin domains as suggested by various programs and
refined by refmac, the difference of between the Rs of the twinned
refinement and the non-twinned refinement are constantly rather
little: 0.143/0.174 for the twinned case, 0.218/0.275 for the
non-twinned case. This seems rather low to me for a quite high twin
fraction. Plus the R-factors for the twinned case are really low for a
1.9AA structure. As expected, the maps from the twin treatment are a
bit nicer that for the non-twinned treatment.
Any reasons for concerns or just a very rigid structure that refines
really well or refmac handling twinning really nicely?
Thanks for any input
Jan
--
Jan Abendroth
deCODE biostructures
Seattle / Bainbridge Island WA, USA
work: JAbendroth_at_decode.is
home: Jan.Abendroth_at_gmail.com
Dear Jan,
The result looks reasonable to me.
Twinning has two effects:
The effective ration of observations/variables decreases with increasing
twinning fraction.
The datasets become better as there are less weak and strong reflections.
This leads to a better fit so that your results do not surprise me.
Yours
Wim Burmeister
--
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Wim Burmeister
Professeur, Membre de l'Institut Universitaire de France
Unit of Virus Host Cell Interactions (UVHCI) UMR5233 UJF-EMBL-CNRS
6 rue Jules Horowitz
B.P. 181, F-38042 Grenoble Cedex 9 FRANCE
E-mail: [EMAIL PROTECTED]
Tel: +33 (0) 476 20 72 82 Fax: +33 (0) 476 20 94 00
http://www.uvhci.fr
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