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The Bruker programs SAINT and TWINABS can integrate and scale up to four
overlapping lattices simultaneously and we have obtained excellent
results using these programs on several twinned proteins similar to the
case you describe. This is routine practice in small molecule
crystallography. The program EVALCCD is also reputed to be able to
integrate such twins. However with sufficient patience it is often
possible to get untwinned crystals by varying the conditions (e.g.
increasing the crystallization temperature by 10 degrees).
George
m.oldham wrote:
We have what seems to be a unique twinning problem. We have
obtained crystals in different conditions and temperatures and these
crystals routinely diffract
to 1.4 Angstroms belonging to same C2 space group with dimensions
(124.15 x 50.49 x 41.38 90, 108.84, 90). However. these crystals show
two independent lattices of equal intensities with crystal orientations
of (twin1: rotx 97.4 roty 7.0 rotz -154.3; twin2: rotx -82.6 roty -7.0
rotz 11.2) With several crystals processed with HKL2000 we observe a 180
degree difference in rotx, an opposite sign to roty and usually a 35
degree difference in rotz. Unfortunately, this twinning causes
the spots to have various degrees of overlap from easily resolvable to
those which are completely superimposable. The integrated and scaled
data give Rsym values of 5-10% and we are able to use the data for
molecular replacement achieving a adequate solution
with reasonably elevated R and Rfree values. Removing overlapped spots
from our highly redundant and complete data results in incomplete data
with the same high redundancy since the removed overlapped reflections
seem to be symmetry related. Does anyone have ideas of how we could
better separate our overlapped reflections and/or what might be the
cause of this twinning phenomenon. If possible we have selenomethionine
data that we would like to use with this structure. Thanks for any help.
Michael Oldham
[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
Purdue University
West Lafayette, IN
--
Prof. George M. Sheldrick FRS
Dept. Structural Chemistry,
University of Goettingen,
Tammannstr. 4,
D37077 Goettingen, Germany
Tel. +49-551-39-3021 or -3068
Fax. +49-551-39-2582
