Human growth hormone inclusion bodies present native-like secondary and tertiary structures which can be preserved by mild solubilization for refolding.

Background: Native-like secondary structures and biological activity have been described for proteins in inclusion bodies (IBs). Tertiary structure analysis, however, is hampered due to the necessity of mild solubilization conditions. Denaturing reagents used for IBs solubilization generally lead to the loss of these structures and to consequent reaggregation due to intermolecular interactions among exposed hydrophobic domains after removal of the solubilization reagent. The use of mild, non-denaturing solubilization processes that maintain existing structures could allow tertiary structure analysis and increase the efficiency of refolding.

Results: In this study we use a variety of biophysical methods to analyze protein structure in human growth hormone IBs (hGH-IBs). hGH-IBs present native-like secondary and tertiary structures, as shown by far and near-UV CD analysis. hGH-IBs present similar λ intrinsic Trp fluorescence to the native protein (334 nm), indicative of a native-like tertiary structure. Similar fluorescence behavior was also obtained for hGH solubilized from IBs and native hGH at pH 10.0 and 2.5 kbar and after decompression. hGH-IBs expressed in E. coli were extracted to high yield and purity (95%) and solubilized using non-denaturing conditions [2.4 kbar, 0.25 M arginine (pH 10), 10 mM DTT]. After decompression, the protein was incubated at pH 7.4 in the presence of the glutathione-oxidized glutathione (GSH-GSSG) pair which led to intramolecular disulfide bond formation and refolded hGH (81% yield).

Conclusions: We have shown that hGH-IBs present native-like secondary and tertiary structures and that non-denaturing methods that aim to preserve them can lead to high yields of refolded protein. It is likely that the refolding process described can be extended to different proteins and may be particularly useful to reduce the pH required for alkaline solubilization.