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
If you are trying to purify recombinant protein with His-tag as you have mentioned E.coli BL21(DE3) as an expression vector system, you need to purify your protein by increasing concentrations of imidazole. I would recommend you below steps to follow:
1) Centrifuge lysate for 15 min. at 6500 rpm
2) Add urea buffer (8M) pH 8.0 and sonicate ( 3 cycles for 30 sec at an interval of 1 min, or repeat the cycles depending on viscosity of lysate) (8 ml of buffer recommended for 100 ml of culture pallet)
3) Equilibrate Ni resin column with urea buffer pH 8.0 (8M) for 30 min.
4) Apply and incubate culture lysate to the column for 30 min (before applying to column lysate should be centrifuged for 30 min at 4oC at 10,000 rpm).
5) Wash column with urea buffer (8M) pH 8.0
6) Wash column with urea buffer (8M) pH 7.4
7) Wash column with increasing concentrations of imidazole in urea buffer pH 7.4 (5mM, 10mM, 15mM, 20mM)
8) Finally, collect the fraction (each 1 ml) by applying 200mM imidazole
Hopefully, You will get the purified fraction of desired protein.
It appears that you have a protein that is extremely insoluble when overexpressed in E. coli. You can try dissolving the insoluble protein in concentrated guanidine hydrochloride or guanidine isothiocyanate. Alternatively, you can try to express it as a soluble protein by coexpression with chaperones and lowering the expression temperature. You could also try expressing it as a fusion with a soluble protein, such as maltose binding protein.
it looks like insoluble expression. Sometimes it can happen if the induction is too large and too much protein is expressed very quickly, Try one or more of the following, lowering the temperature to 16-18degC reduce the induction chemical concentration, harvest the protein earlier after a few hours rather than overnight induction and finally if that fails try autoinduction as this varies the induction chemical concentration with time and is a gentler way of induction.
Your protein is getting overexpressed and the protein folding machinery of E.coil is unable to refold it.so it appears in the insoluble / sediment.So before proceeding for affinity column it has to be solubilized as suggested above. All the best.
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