Dear all, I have two isomorphous crystals of the same protein. One crystal, let's call it 'derivative', was soaked with 10 mM CoCl2 whereas the other, let's call it 'original', was not. Both crystals were otherwise grown under identical conditions (see below) and treated the same. In the derivative, I see some puzzling electron density which I do not see in the original (find two pictures under the links below; the waters in the figures are just put in for your convenience, they were no part of the refinement). The density forms a planar hexagon of spheres with another sphere in the exact center. The distance from corner to corner is about 3.0 A but varies. The distance from one corner to the center is about 3.1 A. The hexagon is almost symmetrical as the angles enclosed by two edges are about 120° each. This density shows up at two positions, once located between two aspartate residues and once between an aspartate and a tyrosine residue. These are, however, no special postions. It seems obvious that this density is caused by the presence of Co(II) since it only shows up in the derivative and also coincides with peaks in the difference fourier map. I am unable to interpret it in a way that makes sense. Could anyone of you help me figure out what to build in there?
Crystallization condition for both original and derivative was 200 mM Tris pH 8.8, 200 mM NaCl, 21% PEG 6000, 20% glycerol. The high-resolution limit of the dataset is 2.0 A. Data were collected at lambda=0.981 A. Anomalous data were collected at Co peak wavelength (weak SigAno but good enough for difference fourier map). links: http://imageshack.us/a/img89/9376/unknowndensity1q.png http://imageshack.us/a/img696/7135/unknowndensity2.png Thank you in advance! Joern ****************************************** Address: Joern Krausze Molecular Structural Biology Helmholtz Centre for Infection Research Inhoffenstrasse 7 38124 Braunschweig Germany Email: joern.krau...@helmholtz-hzi.de Phone: +49 (0)531 6181 7023 (office) +49 (0)531 6181 7020 (lab) ****************************************** ________________________________ Helmholtz-Zentrum für Infektionsforschung GmbH | Inhoffenstraße 7 | 38124 Braunschweig | www.helmholtz-hzi.de Vorsitzende des Aufsichtsrates: MinDir’in Bärbel Brumme-Bothe, Bundesministerium für Bildung und Forschung Stellvertreter: Rüdiger Eichel, Abteilungsleiter Niedersächsisches Ministerium für Wissenschaft und Kultur Geschäftsführung: Prof. Dr. Dirk Heinz; Ulf Richter, MBA Gesellschaft mit beschränkter Haftung (GmbH) Sitz der Gesellschaft: Braunschweig Handelsregister: Amtsgericht Braunschweig, HRB 477
