Substitution of proline 306 in the reverse transcriptase domain of hepatitis B virus regulates replication

The proline residue at position 306 in hepatitis B virus (HBV) reverse transcriptase (rtP306) has been suggested to constrain the conformation of the alpha-helices in the thumb subdomain that interacts with the viral DNA template-primer. To study the impact of residue rt306 in HBV replication further, 11 site-directed mutants were constructed that substituted rtP306 with different amino acids. The replicative competencies of these mutants were assayed by HepG2 cell transfection and real-time PCR. When rtP306 was substituted with glycine or threonine, the replication competency of these mutants was drastically reduced to 1.96 and 4.51% of the wild-type HBV level, respectively. When rtP306 was substituted with glutamic acid, the replicative competency of the mutant increased up to 9.4-fold compared with wild-type virus. The results also showed that changes in the replicative competency of these constructed mutants were not associated with functional changes of HBV enhancer I. These results indicate the importance of amino acid(s) at the interface between the thumb and palm subdomains in modulating the replicative competency of HBV isolates. This regulatory residue(s) could serve as a new target for the development of anti-HBV drugs.