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Dear all,
I recently collected a data set at 1.9 A resolution of a protein mutant and I
tried molecular replacement. Space group seems to be P212121 even though there
are some exceptions in the systematic absences.
MR solutions of the rotation function are the following:
SOLUTIONRC 1 2.04 127.32 0.72 0.0000 0.0000 0.0000 36.7 0.0 1
SOLUTIONRC 1 177.96 52.68 180.72 0.0000 0.0000 0.0000 36.7 0.0 2
SOLUTIONRC 1 66.50 19.00 106.00 0.0000 0.0000 0.0000 14.6 0.0 3
SOLUTIONRC 1 113.50 161.00 286.00 0.0000 0.0000 0.0000 14.6 0.0 4
SOLUTIONRC 1 173.17 116.02 215.83 0.0000 0.0000 0.0000 14.6 0.0 5
SOLUTIONRC 1 6.83 63.98 35.83 0.0000 0.0000 0.0000 14.6 0.0 6
SOLUTIONRC 1 133.94 156.89 214.72 0.0000 0.0000 0.0000 14.2 0.0 7
SOLUTIONRC 1 46.06 23.11 34.72 0.0000 0.0000 0.0000 14.2 0.0 8
The Matthews coefficient (2.36) shows that there should be 2 molecules in the
asymmetric unit.
I didn't use the BMAX 90 option. I also tried to refine only one molecule and
then to calculate the map on the whole asymmetric unit and what I saw was the 2
molecules rapresented by the first two solutions.
Using the first 2 solutions and refining them (with 2 different programs,
REFMAC and SHELXL) I obtain an R(free) of about 30% and R value of 21% (after
intruducing 120 water molecules). The 2fo-fc map is well defined and the fo-fc
doesn't show any significant density peaks.
I wonder why I can't lower the R factor below 20 % and why the R(free) is so
high.
Thanks in advance
Annalisa
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Dr. Annalisa Guerri
Dipartimento di Chimica
Via A. Moro
53100 Siena
Tel: +39 055 42 09 234
email: annalisa@indy1.chim.unifi.it
guerri@alpha.cerm.unifi.it
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