title: An Aptamer against the Matrix Binding Domain on the Hepatitis B Virus Capsid Impairs Virion Formation.
abstract: The hepatitis B virus (HBV) particle is an icosahedral nucleocapsid surrounded by a lipid envelope containing viral surface proteins. A small domain (matrix domain [MD]) in the large surface protein L and a narrow region (matrix binding domain [MBD]) including isoleucine 126 on the capsid surface have been mapped, in which point mutations such as core I126A specifically blocked nucleocapsid envelopment. It is possible that the two domains interact with each other during virion morphogenesis. By the systematic evolution of ligands by exponential enrichment (SELEX) method, we evolved DNA aptamers from an oligonucleotide library binding to purified recombinant capsids but not binding to the corresponding I126A mutant capsids. Aptamers bound to capsids were separated from unbound molecules by filtration. After 13 rounds of selections and amplifications, 16 different aptamers were found among 73 clones. The four most frequent aptamers represented more than 50% of the clones. The main aptamer, AO-01 (13 clones, 18%), showed the lowest dissociation constant (Kd) of 180 ± 82 nM for capsid binding among the four molecules. Its Kd for I126A capsids was 1,306 ± 503 nM. Cotransfection of Huh7 cells with AO-01 and an HBV genomic construct resulted in 47% inhibition of virion production at 3 days posttransfection, but there was no inhibition by cotransfection of an aptamer with a random sequence. The half-life of AO-01 in cells was 2 h, which might explain the incomplete inhibition. The results support the importance of the MBD for nucleocapsid envelopment. Inhibiting the MD-MBD interaction with a low-molecular-weight substance might represent a new approach for an antiviral therapy.
  
  
  OBJECTIVE
  Approximately 240 million people are persistently infected with HBV. To date, antiviral therapies depend on a single target, the viral reverse transcriptase. Future additional targets could be viral protein-protein interactions. We selected a 55-base-long single-stranded DNA molecule (aptamer) which binds with relatively high affinity to a region on the HBV capsid interacting with viral envelope proteins during budding. This aptamer inhibits virion formation in cell culture. The results substantiate the current model for HBV morphogenesis and show that the capsid envelope interaction is a potential antiviral target.
authors.affiliation: Institute of Virology, Helmholtz Zentrum München, Neuherberg, Germany Department of Virology, Faculty of Veterinary Medicine, Zagazig University, Sharkia Governorate, Egypt.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Orabi
authors.affiliation: Institute of Virology, Helmholtz Zentrum München, Neuherberg, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Bieringer
authors.affiliation: Protein Expression and Purification Facility, Institute of Structural Biology, Helmholtz Zentrum München, Neuherberg, Germany.
authors.forename: Arie
authors.initials: A
authors.lastname: Geerlof
authors.affiliation: Institute of Virology, Helmholtz Zentrum München, Neuherberg, Germany volker.bruss@helmholtz-muenchen.de.
authors.forename: Volker
authors.initials: V
authors.lastname: Bruss
mesh_terms: D019943:Amino Acid Substitution; D000998:Antiviral Agents / Q000737:chemistry / Q000494:pharmacology; D052157:Aptamers, Nucleotide / Q000737:chemistry / Q000494:pharmacology; D002213:Capsid / Q000378:metabolism*; D045744:Cell Line, Tumor; D006515:Hepatitis B virus / Q000502:physiology*; D006801:Humans; D020125:Mutation, Missense; D017434:Protein Structure, Tertiary; D019065:Virus Assembly / Q000187:drug effects* / Q000235:genetics
chemical_list: D000998:Antiviral Agents; D052157:Aptamers, Nucleotide