Thank you for your efforts!
@BR: Yes, I do have anomalous data which indicate that the density stems
from Co(II) or anything else that shows significant anomalous dispersion
at 1.6083 A. I just cannot picture 7 Co(II) ions forming a perfectly
planar hexagonal structure with one Co(II) in the center. Even alternating
Co(II) and Cl- ions or anything similar make no chemical sense. I might
simply lack the chemical understanding, though.
@bob: I checked the I6P. With a diameter of about 8.3 A is it 2 A too
wide.
Regards,
Joern
******************************************
Address:
Joern Krausze
Molecular Structural Biology
Helmholtz Centre for Infection Research
Inhoffenstrasse 7
38124 Braunschweig
Germany
Email: [log in to unmask]
Phone: +49 (0)531 6181 7023 (office)
+49 (0)531 6181 7020 (lab)
******************************************
On Thu, 1 Nov 2012, Joern Krausze wrote:
> 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: [log in to unmask]
> Phone: +49 (0)531 6181 7023 (office)
> +49 (0)531 6181 7020 (lab)
> ******************************************
>
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