 |
 |
Dear All,
I am facing difficulty in interpreting an unknown density on a surface tyrosine residue. It appears like an O-modified tyrosine. Two lysines and one histidine are other residues in its proximity.
My storage buffer contains 20mM HEPES, 200mM NaCl and 2mM DTT. The protein was purified with an imidazole gradient and buffer exchanged with the storage buffer. Crystallization buffer
s include 2.0 M Ammonium sulfate, 0.2 M Na K tartarate and 0.1 M Na citrate, pH 5.6. 10% Glycerol and 3.2 M Ammonium sulfate were used as cryo. The density was too small for tartrate, while the Fo-Fc map showed some positive density around a fully occupied glycerol. I was not able to model any of the other buffer components in it.
Attached are the links to the images of the structure. Blue is 2Fo-Fc, contoured to 1σ and green is Fo-Fc contoured to 3σ. The structure was solved to 2.0 Å resolution. The density appears in all the crystals solved in this condition. I would like to know if anyone has come across such a density.
TIA for your suggestions.
Gayathri Subash
Research Scholar,
Lab No: 309,
Structural Biology Lab,
IIT Madras,
Chennai-600036