Dear All,
I am refining the crystal structure of an E. coli expressed protein
at 2.65 A resolution. The crystals grew in
0.1 M MES pH6, 0.7 M sodium formate pH 6. Ni-NTA was used in the
purification.
There are four molecules in the asymmetric unit. A particular histidine
in each molecular has clear, strong extra density which looks like a
metal bonded to an imidazole nitrogen (distance approx 2 A) with three
other co-ordinating atoms in a triangular planar arrangement (see
attached screen shot for unbiased extra density, atoms are only put in
the density for illustrative purposes).
Has anyone seen anything like this ? Any suggestions ?
thanks very much
Stephen
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Dr. Stephen Cusack, FRS
Head of Grenoble Outstation of the European Molecular Biology Laboratory (EMBL)
Group leader in structural biology of protein-RNA complexes and viral proteins
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