Hello BB I am working with small protein-protein complex of Molecular weight 40kDa. This protein expresses well and soluble in 20mM Tris-Cl pH-8.0 and 50mM of KCl, could be concentrated upto 20mg per ml in this buffer. I have purifed this protein with Ni-NTA resin and they are free from any contaminants. Therefore, this protein have been directly used for the screening. I started crystallisation screening with INDEX screen of hampton research and some other lab made random screen. It precipitates immediately in the most of the condition (85%) except those conditions where PEG and Jeffamine are as precipitant with HEPES or Tris-Cl buffers above the pH value 7. Another conditions where it doesnot precipiatate are 0.1M Tris-Bis pH-5.5 + 3M NaCl , and 0.1M Na-Acetate pH-4.5 + 3M NaCl. This is a strange behaviour of the protein complex. I would appreciate the suggestions in this concern. What are the other possibilties, which can be explored through this observation? Although I can proceed for the screening with the other screens like PEG Screen or crystal screen or some other random screens, it would be better to find out the root problem of the immediate precipiation of the proteins in the crystallisation conditions.
Thanks in advance Jhon
