Please read our suggestions below:
-Maintain low protein concentrations 10-50 µg/mL.
-Disulfide bonds help to stabilize native proteins; add a redox pair such as GSH (reduced glutathione)
-GSSG (oxidized glutathione) at a ratio of 10:1 with GSH concentration of 2-5 mM. Such a redox pair is helpful to create an oxidizing potential to break and build new S-S bonds during the folding process.
-Remove denaturants slowly by dilution or dialysis; glycine (50 mM, pH 9.0, 5 mM EDTA) helps to solubilize the proteins. If GuHCl (guanidinium HCl) is used, add 2 M urea because urea helps to stabilize the protein folding, too.
-Add detergents at a very low concentration such as 0.1-0.5% NP-40 or 0.005% (v/v) Tween 20.
-Include co-solvents to stabilize the proteins such as glycerol (5-20%) or PEG 8000 or glucose or sucrose. (10 %)
-Certain anions (e.g., phosphate or sulfate) or cations (e.g., MES or HEPES) have positive effects, too; include salt and maintain a neutral pH such as 100 mM KCl, or 150-500 mM NaCl, 2 mM MgCl2.
-Avoid protein degradation by adding protease inhibitors such as 0.5 mM PMSF, 0.005-2 µg/mL aprotinin, 2 µg/mL Pepstatin, or 2-5 µg/mL leupeptin.
-Dialysis of a phosphate buffer when against calcium will result in a calcium phosphate precipitate. If CaCl2 is needed for subsequent enterokinase digestion (10 mM Tris pH 8, 10 mM CaCl2), remember to add CaCl2 after dialysis is complete.
Alternatively, you can use the Pierce Protein Refolding kit (cat. No. 89867)
Find additional tips, troubleshooting help, and resources within our Protein Purification and Isolation Support Center.