Dear all I am working on a 30 kDa membrane protein which forms a functional dimer. The protein is His-tagged at N-terminal. In small scale expression screening from whole cells, there is only a single band on Western blot at 30 kDa. But, after purification, additional bands appear at 60 and 120 kDa on SDS-PAGE and Western blot. On size exclusion with Superdex 200, a large proportion elute near the void volume (8 ml).
Detail purification For small scale screening, I lysed cells in 20 mM Tris pH 8, 100 mM NaCl, 1 mg/ml lysozyme, 1 % DDM and DNAse for 2 hours and then centrifuged at 16000 g. I then checked the supernatant on SDS-PAGE and scale it up for purification. For purification, I use the buffer 50 mM Tris pH 8, 300 mM NaCl, 20 mM imidazole, 0.05 % DDM (two times CMC of DDM). Is there suggestion to get homogeneous protein? Thank you. Theresa
