Editing His-TEV-Tat-NRF2 Purification

1. Transform Rosetta2(DE3)pLysS (EMD) or BL21(DE3)pRare2 pLysS with plasmid 

2. Pick a few colonies and grow them in 80 ml LB/K/C, at 37 oC 

3. Add 10 ml of starter culture to 1 liter LB/K/C, at 37 °C until OD600nm reached 0.6. 

4. Add 1 M IPTG to final conc of 1 mM, grow for 4 h at 37 oC. 

5. Spin down cells, add Lysis buffer (50 mM Tris–HCl, pH 8.0, 400 mM NaCl, 5% glycerol, 0.1 mM EDTA, 2 mM tris(2-carboxyethyl)phosphine (TCEP) or beta-ME). Add at a ratio of 10 ml of lysis buffer per 1 g of wet weight E. coli. 

6. Freeze and thaw once. 

7. Homogenize or sonicate. 

8. Spin at 26,000g for 30 min at 4 °C. 

9. Wash inclusion bodies in the pellet twice by resuspension in Inclusion Body Wash Buffer <br>(50 mM Tris–HCl, pH 7.9, 400 mM NaCl, 5% glycerol, 0.1 mM EDTA, 2 mM tris(2-carboxyethyl)phosphine (TCEP) or beta-ME), 1% Triton X-100). 

<br>10. Spin again as step 8. 

11. Wash again with Lysis Buffer. 

12. Dissolve inclusion bodies in denaturing buffer (50 mM Tris–HCl, 6 M guanidine hydrochloride (GdnHCl), 2 mM TCEP, pH 7.9). 

13. Spin at 26,000g for 30 min. 

14. Load supernatant (1 ml) to on a 24-ml Superose 6 10/300 GL column. 

15. Elute with mobile phase (50 mM Tris–HCl, 3 M GdnHCl, 2 mM TCEP, pH 7.9) at a flow rate of 0.25 ml/min. 

16. Solubilize inculsion body in denaturing buffer (10 mM Tris–HCl, 3 M GdnHCl, 0.1 mM dithiothreitol (DTT), pH 7.9), and dilutediluted 20-fold,, i.e., add 10 ul of denatured protein into 190 ul of base buffer (10 mM Tris–HCl, 0.1 mM DTT, pH 7.9) supplemented with specific refolding additives, such as 0.6 M arginine. 

Best condition for NRF2 refolding: 25 mM Tris–HCl, 0.6 M arginine, 2 mM TCEP, pH 7.9 

17. Incubated for 1 h at 22 °C and then measure absorbance at 320 nm using spectrophotometer or microplate reader. Use one well with water as blank and one well without refolding additive as unfolded control. <br>

Example additives: 50% glycerol, 0.6 M arginine, 0.3 M arginine, sodium taurodeoxycholate, Polyethylene glycol, β-mercaptoethanol, dithiotreitol (DTT), dithioerythritol, or cysteine, Glucose, 0.75 M Trehalose, 1 M Glycine betaine, 0.5 M Mannitol, 0.1 M Potassium citrate, mannitol, L-Arginine, potassium citrate, CuCl2, proline, xylitol, NDSB 201, CTAB and K2PO4.<br><br><br>

18. Analyse refolding efficiency by analytical SEC (AnSEC). Equilibrate a Shodex Protein KW802.5 column with mobile phase (50 mM Tris–HCl, 250 mM NaCl, 5% glycerol, 0.1 mM DTT, pH 7.9). Load 200 ul of refolded protein (10–40 ug) onto the column and elute protein with mobile phase at a flow rate of 1 ml/min. Monitor at 280 nm (A280nm) and 215 nm (A215nm). 

<br>19. Concentrate and desalting using hydrophobic interaction chromatography (HIC). 

*Equilibrate a 1-ml Phenyl-Sepharose FF (low substitution) column equilibrated with Buffer A (50 mM Tris–HCl, 2 mM TCEP, pH 7.5, 800 mM ammonium sulfate)<br>* Elute protein with phase B (50 mM Tris–HCl, 2 mM TCEP, pH 7.5).

20. Add 2X buffer TEV buffer (100 mM Tris–HCl, pH 7.9, 300 mM NaCl, 1 mM EDTA, and 0.2 mM DTT, 10% glycerol) to adjust to final conc: 50 mM Tris–HCl, pH 7.9, 150 mM NaCl, 0.5 mM EDTA, and 0.1 mM DTT, 5% glycerol) and cleaved with 0.1 M equivalents of His6-tagged TEV protease for 2 h at 22 °C. 

21. Pass digested protein through a 1 ml Ni-NTA agarose column, collect flow through. 

22. Concentrate protein using spin concentrator. 

23. Store protein at -80 oC.<br>