Study of the putative fusion regions of the preS domain of hepatitis B virus

In a previous study, it was shown that purified preS domains of hepatitis B virus (HBV) could interact with acidic phospholipid vesicles and induce aggregation, lipid mixing and leakage of internal contents which could be indicative of their involvement in the fusion of the viral and cellular membranes (Núñez, E. et al. 2009. Interaction of preS domains of hepatitis B virus with phospholipid vesicles. Biochim. Biophys. Acta 17884:417–424). In order to locate the region responsible for the fusogenic properties of preS, five mutant proteins have been obtained from the preS1 domain of HBV, in which 40 amino acids have been deleted from the sequence, with the starting point of each deletion moving 20 residues along the sequence. These proteins have been characterized by fluorescence and circular dichroism spectroscopy, establishing that, in all cases, they retain their mostly non-ordered conformation with a high percentage of β structure typical of the full-length protein. All the mutants can insert into the lipid matrix of dimyristoylphosphatidylglycerol vesicles. Moreover, we have studied the interaction of the proteins with acidic phospholipid vesicles and each one produces, to a greater or lesser extent, the effects of destabilizing vesicles observed with the full-length preS domain. The ability of all mutants, which cover the complete sequence of preS1, to destabilize the phospholipid bilayers points to a three-dimensional structure and/or distribution of amino acids rather than to a particular amino acid sequence as being responsible for the membrane fusion process.