The nature of hepatitis B virus (HBV) particle associated DNA polymerase was studied in relation to various enzyme inhibitors including antiviral agents. HBV DNA polymerase required high concentration of MgCl2(> 30 mM) and neutral pH for its full activity. p-chloromercuribenzoate was a strong inhibitor (85% inhibition at 1 mM) but N-ethylmaleimide had much less inhibitory effect (20% inhibition at 10 mM). Phosphonoformic acid showed the greatest inhibitory effect on HBV-DNA polymerase (almost complete inhibition at 100 microM) among phosphocompounds tested. Adenine arabinoside triphosphate (ara-ATP) and cytosine arabinoside triphosphate (ara-CTP) were competitive inhibitors with respect to their respective deoxyribonucleoside triphosphate (dATP and dCTP). Ara-CPT was a stronger inhibitor of HBV-DNA polymerase compared to ara-ATP. Ki values for ara-ATP and ara-CTP were 15.0 microM and 11.7 microM , respectively. HBV-DNA polymerase is characteristic in its ionic requirements and susceptibilities to certain inhibitors.
DNA-Directed DNA Polymerase/antagonists & inhibitors ; DNA-Directed DNA Polymerase/metabolism* ; Hepatitis B Virus/enzymology* ; Human

BACKGROUND/AIMS: To develop a novel treatment method for hepatitis B virus (HBV) infection, we aimed to make a human monoclonal antibody inhibiting reverse transcriptase (RT) activity of P protein which was important in HBV replication by using phage display technique. Therefore, we analysed the usability of human monoclonal antibody as a protein based gene therapy. METHODS: Reverse transcriptase/polymerase (RT/POL) functional motif of P protein of HBV was cloned in pMAL-c vector and expressed as maltose binding fusion protein form. The RT/POL recombinant protein (pMRT/POL) was purified by amylose resin column. Using human single chain Fv phage antibody library with 1.1x10(10) size, human antibody against pMRT/POL was selected with BIAcore panning. Selected antibody fragments were analyzed for the activity of RT inhibition. Finally, they were analyzed for the affinity with BIAcore and the complementarity determining regions with nucleotide sequencing. RESULTS: pMRT/POL recombinant protein expressed in E. coli showed RT activity, 1microgram of recombinant protein had an activity equivalent to 5 unit of MMLV RT. By BIAcore panning, we could select 3 clones; POL-A5, POL-B8 and POL-B12. Each clone's RT inhibiting activity were 52-82%, affinity against antigen were 8.15x10(-8) M to 1.75x10(-6) M. CONCLUSIONS: Human monoclonal antibodies produced in this study showed low affinity, but efficiently inhibited the activity of RT in vitro. If POL-A5, POL-B8, and POL-B12 can be converted to intracellular antibody form, it can be used for protein-based gene therapy by inhibiting the replication through the neutralization of polymerase protein of HBV.
Antibodies, Monoclonal/biosynthesis/genetics/*pharmacology ; Complementarity Determining Regions/chemistry ; Gene Products, pol/*antagonists & inhibitors/genetics/immunology ; Genetic Vectors ; Hepatitis B virus/enzymology/genetics ; Humans ; Peptide Library ; RNA-Directed DNA Polymerase/genetics/*immunology ; Recombinant Fusion Proteins/biosynthesis/genetics ; Reverse Transcriptase Inhibitors/chemistry/metabolism/*pharmacology