Dear all,

 

We have found a huge Fo-Fc density close to cysteine residue (see attached image) in the structure with resolution of 1.2A. In the crystallization condition, we have PEG 3350, Potassium phosphate monobasic, glycerol and protein was in Tris and NaCl. Before freezing the crystals were soaked in mother liquor containing sodium dithionite.

 

I have tried different modified cysteine (CSX, CSO, OCS, CME, CSS, SNC, CSD, CXM, SCH, CSU) from the library and also SO₃, SO₂ and peroxide. But in all the screenings we do see some part of Fo-Fc density unaddressed at 3 sigma.

 

Does anyone have an idea about what this density could be? Covalent modification?

 

Thanks.

 

Kind regards,

Lumbini

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