[phenixbb] Magnesium or calcium

vellieux frederic.vellieux at ibs.fr
Sat Mar 2 10:14:20 PST 2013


In principle if you have access to a tuneable X-ray beam and that you go 
to higher wavelengths (towards 2.5 and higher) then you'd get 
significant anomalous signal for Calcium and no such significant 
anomalous signal for Mg. Not many of these beam lines (with high flux) 
around though. At lower wavelengths there is less signal and therefore 
it becomes more and more problematic (care must be taken to collect the 
data). Still ca. 1.3 electrons anomalous signal at 1.54 A wavelength for Ca.



On 02/03/13 18:43, Daniel Slade wrote:
> I have several structures that has multiple known calcium binding sites, and I found a new site that seems to accept calcium or magnesium.  I say this because if a magnesium is put in the structure, the bond lengths are ~ 2.1.  But if you put a calcium in it, they go to ~2.6.  All of these  refinements were done without ReadySet, which I recently used with metal restraints and it seemed to change the bond length of calcium to ~2.4.  I'm a bit confused as to what to do here as either metal seems to be right.  Worth noting, this is a very strong metal binding site that can't be removed with 10 mM EDTA.
> Any help here on how to figure this out which ion this is would be great.
> Thanks in advance
> Dan
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Fred. Vellieux (B.Sc., Ph.D., hdr)
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