I have expressed a protein in E.coli BL21(DE3) expression vector system.This targeted protein always remains in sediment. For the elution of this protein I have tried many times to change the pH of elution buffers at 7.5,8,9 pH of 50mM Tris-Hcl and 20mM Immidazole and also after sonication i have washed sediment three times with 2M urea and each time centrifuged at 10000rp for 10 minutes.After that 8M urea was added into the sediment and incubated it at 4c for 6 hours. Then centrifuged and supernatant was loaded onto a Ni-NTA column and purified it with the series of washing and elution buffers but all efforts were remaind fruitless. After SDS running i saw that a protein was in sediment. Please give me suggestions What should I do.
Thans
Farman Ali