ABSTRACT
The most frequent mutation of the human hepatitis B virus (HBV) core antigen occurs at amino acid 97. Recently, a phenylalanine (F)-to-leucine (L) mutation at this position (mutant F97L) in HBV surface antigen subtype ayw has been shown to result in an immature secretion phenotype, which is characterized by the nonselective export of an excessive amount of virions containing minus-strand, single-stranded HBV DNA. While subtype aywmutant F97L has been found in Europe, the major reservoir of HBV resides in Asia and Africa. We report here that the immature secretion phenotype indeed can be found in an HBV strain (subtypeadr) prevalent in Asia, changing from an isoleucine (I) to a leucine (mutant I97L). Despite its immature secretion phenotype, theadr variant I97L replicates as well as its parentaladr wild-type I97I, supporting the conclusion that the extracellular phenotype of immature secretion is not a consequence of the intracellular HBV DNA replication defect. Further studies demonstrated that it is the acquisition of a leucine, rather than the loss of a wild-type amino acid at codon 97, that is important for immature secretion. We conclude that immature secretion is a subtype-independent phenotype and deficiency in intracellular DNA synthesis is a subtype-dependent phenotype. The former is caused by thetrans-acting effect of a mutant core protein, while the latter by a cis-acting effect of a mutated nucleotide on the ayw genome. These immature secretion variants provide an important tool for studying the regulation of HBV virion assembly and secretion.
The secretory core protein of human hepatitis B virus is expressed on the cell surface.
