Purification and structural analysis of the hepatitis B virus PreS1 expressed from Escherichia coli

The preS1 of hepatitis B virus (HBV) is located at the outermost part of th e envelope protein and possesses several functionally important regions suc h as hepatocyte receptor-binding site and virus-neutralizing epitopes, As t he first step to understand the structure-function relationship for the pre S1 antigen, we have purified the preS1 and performed its structural charact erization by circular dichroism (CD) spectroscopy. The preS1 was purified t o near homogeneity from bacterially expressed glutathione S-transferase (GS T)-preS1 fusion protein by two-step purification, affinity chromatography o n glutathione-agarose column, and cation-exchange chromatography on Mono S column, The CD analysis showed that the purified preS1, which was largely u nstructured in aqueous solution, acquired a significant (16%) alpha -helica l structure when analyzed in 50% trifluoroethanol or 20 mM SDS, The results suggest that the preS1 assumes a mainly unstructured conformation and may form induced secondary structures upon binding to target proteins or under hydrophobic environment. (C) 2001 Academic Press.