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<>We
have recently solved the structure of a protein
complex to and tried different substrates. Among these, we obtained a different crystal form: the crystal diffracts up to 2.9A and can be indexed in hexagonal or trigonal space groups with lattice parameters a=175 b=175 c=290. 90,90,120°. All diffraction spots are indexed in the frames by mosflm. Refinement of the unit cell goes fine and final processing with scala give Rsym of 0.13-0.15 for the different space groups. However the unit cell seems very large and imposes the asymmetric unit to contain 6 molecules in the case of P622 or Data analysis with sfcheck, detwin, and Yeates server indicates the crystal is twinned with twin fraction of ~0.39. Taking all the possible twin laws for each possible space group, the data were detwinned with program detwin but remained twinned afterwards with a new suggested twin fraction of ~0.20 when analysed by sfcheck and others. detwinned or not, Patterson analysis yields three high peaks at (0.666 0.333 0.052), (0.333 0.666 0.052) and (0.666, 0.333, 0.000) which suggest a pseudo translation (or a smaller possible unit cell (?) which was not given by mosflm). When using untwined data, cross rotation search with Molrep yields a single rotation peak, although one would expect several solutions. The translations mentioned above have been used but did not yield any good solution so far. When using detwinned data we obtain several cross rotation solutions but with no further success. Could it be possible that the crystal exhibit a reticular merohedral twinning (with a smaller unit cell)? But in this case should the Rsym be much higher than it actually is? Any
help will be welcome -- Thierry GRANIER Unité de Biophysique Structurale Bât B8 Avenue des Facultés Université Bordeaux 1 33405 TALENCE Cedex FRANCE |
