• Journal of Microbiology and Biotechnology
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• v.30 no.9
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• pp.1273-1281
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• 2020

Due to the broad host suitability of viral vectors and their high gene delivery capacity, many researchers are focusing on viral vector-mediated gene therapy. Among the retroviruses, foamy viruses have been considered potential gene therapy vectors because of their non-pathogenicity. To date, the prototype foamy virus is the only retrovirus that has a high-resolution structure of intasomes, nucleoprotein complexes formed by integrase, and viral DNA. The integration of viral DNA into the host chromosome is an essential step for viral vector development. This process is mediated by virally encoded integrase, which catalyzes unique chemical reactions. Additionally, recent studies on foamy virus integrase elucidated the catalytic functions of its three distinct domains and their effect on viral pathogenicity. This review focuses on recent advancements in biochemical, structural, and functional studies of foamy virus integrase for gene therapy vector research.

• Journal of Microbiology and Biotechnology
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• v.27 no.2
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• pp.380-387
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• 2017

The foamy viruses are currently considered essential for development as vectors for gene delivery. Previous studies demonstrated that prototype foamy virus (PFV) can infect and replicate prevalently in a variety of cell types for its exclusive replication strategy. However, the virus-host interaction, especially PFV-transportin3 (TNPO3), is still poorly understood. In our investigation of the role of TNPO3 in PFV infection, we found lower virus production in TNPO3 knockdown (KD) cells compared with wild-type 293T cells. PCR analysis revealed that viral DNAs were mostly altered to circular forms: both 1-long terminal repeat (1-LTR) and 2-LTR in TNPO3 KD cells. We therefore suggest that TNPO3 is required for successful PFV replication, at least at/after the nuclear entry step of viral DNA. These findings highlight the obscure mysteries of PFV-host interaction and the requirement of TNPO3 for productive infection of PFV in 293T cells.

• Journal of Microbiology and Biotechnology
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• v.18 no.6
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• pp.1044-1049
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• 2008

In order to study functional nucleotides in prototype foamy virus (PFV) DNA on specific recognition by PFV integrase (IN), we designed chimeric U5 long terminal repeat (LTR) DNA substrates by exchanging comparative sequences between human immunodeficiency virus type-1 (HIV-1) and PFV U5 LTRs, and investigated the 3'-end processing reactivity using HIV-1 and PFV INs, respectively. HIV-1 IN recognized the nucleotides present in the fifth and sixth positions at the 3'-end of the substrates more specifically than any other nucleotides in the viral DNA. However, PFV IN recognized the eighth and ninth nucleotides as distinctively as the fifth and sixth nucleotides in the reactions. In addition, none of the nucleotides present in the twelfth, sixteenth, seventeenth, eighteenth, nineteenth, and twentieth positions were not differentially recognized by HIV-1 and PFV INs, respectively. Therefore, our results suggest that the functional nucleotides that are specifically recognized by its own IN in the PFV U5 LTR are different from those in the HIV-1 U5 LTR in aspects of the positions and nucleotide sequences. Furthermore, it is proposed that the functional nucleotides related to the specific recognition by retroviral INs are present inside ten nucleotides from the 3'-end of the U5 LTR.

• YAKHAK HOEJI
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• v.52 no.2
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• pp.125-130
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• 2008

The long terminal repeat (LTR) of retroviral DNA genome plays an important role in the integration process by providing substrate recognition site for viral integrase (IN). The dinucleotide CA near the 3'-end of the LTR termini is completely conserved among retoviruses. In order to study specificity of interaction between prototype foamy virus (PFV) IN and its U5 LTR DNA, the effect of mutagenesis of the CA sequence was investigated by studying reactivity of PFV IN to the mutant LTR substrates. Replacement of only the C or the A allowed 60 to 100% of the reactivity of the wild type LTR substrate. In addition, replacement of the C and the A showed 50 to 80% of the reactivity of the wild type LTR substrate, indicating that PFV IN has less specificity on the conserved CA sequence when it is compared to the other retroviral INs. Therefore it is suggested that PFV IN is less dependent on the conserved sequence of LTR termini for its enzymatic reaction.

• Journal of Microbiology and Biotechnology
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• v.20 no.6
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• pp.968-973
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• 2010

In order to study its biochemical properties, the integrase (IN) protein of feline foamy virus (FFV) was overexpressed in Escherichia coli, purified by two-step chromatography, (Talon column and heparin column), and characterized in biochemical aspects. For the three enzymatic reactions of the 3'-processing, strand transfer, and disintegration activities, the $Mn^{2+}$ ion was essentially required as a cofactor. Interestingly, $Co^{2+}$ and $Zn^{2+}$ ions were found to act as effective cofactors, whereas other transition elements such as $Ni^{2+}$, $Cu^{2+}$, $La^{3+}$, $Y^{3+}$, $Cd^{2+}$, $Li^{1+}$, $Ba^{2+}$, $Sr^{2+}$, and $V^{3+}$ were not. Regarding the substrate specificity, FFV IN has low substrate specificities as it cleaved in a significant level prototype foamy virus (PFV) U5 LTR substrate as well as FFV U5 LTR substrate, whereas PFV IN did not. Finally, the 3'-processing activity was observed in high concentrations of several solvents such as CHAPS, glycerol, Tween 20, and Triton X-100, which are generally used for dissolution of chemicals in inhibitor screening. Therefore, in this first report showing its biochemical properties, FFV IN is proposed to have low specificities on the use of cofactor and substrate for enzymatic reaction as compared with other retroviral INs.

• Molecules and Cells
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• v.37 no.2
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• pp.140-148
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• 2014

We identified four basic amino acid residues as nuclear localization signals (NLS) in the C-terminal domain of the prototype foamy viral (PFV) integrase (IN) protein that were essential for viral replication. We constructed seven point mutants in the C-terminal domain by changing the lysine and arginine at residues 305, 308, 313, 315, 318, 324, and 329 to threonine or proline, respectively, to identify residues conferring NLS activity. Our results showed that mutation of these residues had no effect on expression assembly, release of viral particles, or in vitro recombinant IN enzymatic activity. However, mutations at residues 305 (R ${\rightarrow}$ T), 313(R ${\rightarrow}$ T), 315(R ${\rightarrow}$ P), and 329(R ${\rightarrow}$ T) lead to the production of defective viral particles with loss of infectivity, whereas non-defective mutations at residues 308(R ${\rightarrow}$ T), 318(K ${\rightarrow}$ T), and 324(K ${\rightarrow}$ T) did not show any adverse effects on subsequent production or release of viral particles. Sub-cellular fractionation and immunostaining for viral protein PFV-IN and PFV-Gag localization revealed predominant cytoplasmic localization of PFV-IN in defective mutants, whereas cytoplasmic and nuclear localization of PFV-IN was observed in wild type and non-defective mutants. However sub-cellular localization of PFV-Gag resulted in predominant nuclear localization and less presence in the cytoplasm of the wild type and non-defective mutants. But defective mutants showed only nuclear localization of Gag. Therefore, we postulate that four basic arginine residues at 305, 313, 315 and 329 confer the karyoplilic properties of PFV-IN and are essential for successful viral integration and replication.