Hepatitis B Virus Capsid Assembly Is Enhanced by Naturally Occurring Mutation F97L

Abstract

In chronic hepatitis B virus (HBV) infections, one of the most common mutations to the virus occurs at amino acid 97 of the core protein, where leucine replaces either phenylalanine or isoleucine, depending on strain. This mutation correlates with changes in viral nucleic acid metabolism and/or secretion. We hypothesize that this phenotype is due in part to altered core assembly, a process required for DNA synthesis. We examined in vitro assembly of empty HBV capsids from wild-type and F97L core protein assembly domains. The mutation enhanced both the rate and extent of assembly relative to those for the wild-type protein. The difference between the two proteins was most obvious in the temperature dependence of assembly, which was dramatically stronger for the mutant protein, indicating a much more positive enthalpy. Since the structures of the mutant and wild-type capsids are essentially the same and the mutation is not involved in the contact between dimers, we suggest that the F97L mutation affects the dynamic behavior of dimer and capsid.

Thermodynamic origins of protein folding, allostery, and capsid formation in the human hepatitis B virus core protein

“…Thus, the low secretion phenotype associated with L60V may arise from making other functionally important conformers inaccessible or by compromising interactions with key-binding partners. F97L stabilized N relative to I but slightly increased the equilibrium proportion of capsids (Table S1), consistent with reports of enhanced in vitro capsid assembly and immature virion secretion (25,51,52). Because F97 is buried within the hydrophobic core of the four-helix bundle, a structurally diverse region reported to be allosteric (15), it may be that F97L simply accelerates capsid assembly by promoting occupancy of HBc Ass (25).…”

“…5B). F97L slightly increased the extent of capsid assembly (25), but S87D and L60V were WTlike (Table S1). …”

“…We then analyzed HBc mutants that yield viruses with altered phenotypes in patients with chronic HBV infections to see if these phenotypes had origins in the thermodynamics of the native dimer (Table 1). F97L enhances HBV capsid assembly and causes premature virion secretion (25,(51)(52)(53)). L60V causes low-level virion secretion in vivo (53,54).…”

“…capsid assembly have inferred the existence of assembly-active (HBc Ass ) and assembly-incompetent (HBc Inc ) HBc conformations (12,13,21,24,25). However, there are few detailed insights on the thermodynamic origins of structure, allostery, and dynamics for the dimeric HBc 1-149 protomer, where structural plasticity must originate.…”

Core-controlled polymorphism in virus-like particles

“…Insight into empty capsid formation has been obtained in recent years from theoretical (33)(34)(35)(36)(37) and in vitro experimental studies (31,38,39). In this case, a sequential assembly principle has been proposed in which either preformed intermediates or individual structural subunits adhere to a proto-capsomer or initial nucleation center to form a capsid (33,40).…”