Polypeptide 3AB of hepatitis A virus is a transmembrane protein

Hepatitis A virus (HAV) protein 3AB is a membrane-interacting protein containing a stretch of 21 hydrophobic amino acid residues. The nature of its membrane association was studied in detail by analysing various deletion mutants. In vivo and in vitro expression of the wild-type protein and its mutants allowed to demonstrate that the hydrophobic domain interacts with membranes and to define the portions essential for this feature. Furthermore, the results suggest that 3AB behaves as an integral membrane protein. Expression in Escherichia coli showed that 3AB can be isolated, in association with membranes, both in monomeric and in dimeric form. This finding was confirmed in vitro after post-translational incubation of the protein with microsomal membranes. Analysis of deletion mutants demonstrated that the dimerization region colocalises with the hydrophobic transmembrane domain, implicating that HAV 3AB could form oligomers mediated by the interaction of transmembrane alpha-helices.