Physicochemical studies of hepatitis A virus recombinant proteins: interaction with monolayers as membrane models

The production of recombinant proteins of hepatitis A virus (HAV), P1 and F proteins, was achieved in Escherichia coli [A. Bosch et al., Viral Hepatitis and Liver Disease, 1997, p. 27]. Both were recognized by MAbs K2-4F2 and MAK7E7, which means that some discontinuous epitopes are present so they may be used as HAV immunogens, and thus, their interaction with biological membranes is of interest. The surface activity of P1 and F recombinant proteins was very similar, thus indicating their similar hydrophobicity. The saturation concentration resulted to be 0.019 mg ml−1 and 0.022 mg ml−1 at 25°C for P1 and F proteins, respectively. Membrane interaction studies were performed either using diphosphatidylcholine (DPPC) monolayers as a model for biological membranes or using artificial erythrocyte membranes. The kinetics of penetration into both kind of membranes were carried out at different pressures (5 mM m−1, 10 mM m−1, 20 mM m−1 and 32 mM m−1) in a Langmuir film balance at constant temperature (25°C). A different pattern was observed between the P1 and F proteins depending on the kind of membrane. While the P1 protein showed higher activity with the DPPC membrane than with the erythrocyte membrane, the F protein showed higher activity with the last membrane. These different behaviour cannot be explained considering only the amino acid composition since no major differences in charge or hydrophobicity exists between both proteins. However, since the protein lengths are different, the protein folding could not be the same, thus influencing the membrane interaction.