Dear Chris, are there any metal ions in your buffer or in your protein.
We had a similar looking case. A Zn2+ ion bridged two monomers. Our
protein is a Zn2+ binding protein. The Zn2+ originated from some
denatured protein in the drop. No extra Zn2+ was in the crystallization
buffer.
http://www.rcsb.org/structure/5CHT
https://www.nature.com/articles/nsmb.3371
HTH
Guenter
Dear CCP4BB Users,
I've recently solved the ~2.2 angstrom structure of a protein. In my
electron density there are unusual monomer-monomer interfaces
involving pairs of His and Cys residues (see https://ibb.co/wdWBcdk).
Note the positive Fo-Fc density between the four side chains. As there
is not adequate space for a water molecule or metal ion, perhaps the
Cys residues are partially tied up disulfide bonds? However, the
protein looks to be fully monomeric based on LC-MS measurements. Has
anyone else observed crystal-driven formation of disulfide bridges?
Aside from this region, there is no extensive interface between
momoners, and PDBePISA suggests a monomeric state.
Thanks in advance for any advice!
Best wishes,
Chris
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