The density looks an awful lot like a polyatomic anion (sulfate,
phosphate, etc.). It's hard to tell from the fixed images, but it
appears to be tetrahedral. Is there any chance a polyatomic anion could
be in the crystallization solution? Perhaps from the protein stock solution?
Sampath Natarajan wrote:
> Dear All,
>
> Currently I'm modeling one structure with 2.6A data. I could find an
> unknown density which I located in the interface between the three
> similar subunits. This density shows very strong peak, which appears
> until 10 sigma level in the difference map. It seems to be a metal
> ion. But, already I could find two Zn ions in the active site and
> refined well. The aspartic acid of each subunit has very close
> interaction with this density. You can see the pictures, which I have
> attached with this mail. The crystallization condition is 0.05M CaCl_2
> 0.1M Bis-Tris pH 6.5, 30% (/v/v/) PEG monomethyl ether 550. Suggestion
> about this unknown density will be more helpful to find the molecule.
>
> thanks a lot,
>
> Regards,
>
> Sampath
--
------------------------------------------------------------------------
Roger S. Rowlett
Professor
Colgate University Presidential Scholar
Department of Chemistry
Colgate University
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Hamilton, NY 13346
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