Structure and Function of HIV-1 Reverse Transcriptase: Molecular Mechanisms of Polymerization and Inhibition

Christopher Bond Life Sciences Center, Department of Molecular Microbiology & Immunology, University of Missouri School of Medicine, Columbia, MO 65211, USA.
Journal of Molecular Biology (Impact Factor: 4.33). 12/2008; 385(3):693-713. DOI: 10.1016/j.jmb.2008.10.071
Source: PubMed


The rapid replication of HIV-1 and the errors made during viral replication cause the virus to evolve rapidly in patients, making the problems of vaccine development and drug therapy particularly challenging. In the absence of an effective vaccine, drugs are the only useful treatment. Anti-HIV drugs work; so far drug therapy has saved more than three million years of life. Unfortunately, HIV-1 develops resistance to all of the available drugs. Although a number of useful anti-HIV drugs have been approved for use in patients, the problems associated with drug toxicity and the development of resistance means that the search for new drugs is an ongoing process. The three viral enzymes, reverse transcriptase (RT), integrase (IN), and protease (PR) are all good drug targets. Two distinct types of RT inhibitors, both of which block the polymerase activity of RT, have been approved to treat HIV-1 infections, nucleoside analogs (NRTIs) and nonnucleosides (NNRTIs), and there are promising leads for compounds that either block the RNase H activity or block the polymerase in other ways. A better understanding of the structure and function(s) of RT and of the mechanism(s) of inhibition can be used to generate better drugs; in particular, drugs that are effective against the current drug-resistant strains of HIV-1.

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Available from: Kalyan Das, Oct 06, 2015
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    • "The first category consists of the nucleos(t)ide RT inhibitors (NRTIs), which are analogs of the natural nucleosides. Most NRTIs lack a 3’-OH and act as chain terminators by blocking DNA polymerization [1-8]. The other group includes the nonnucleoside RT inhibitors (NNRTIs), which are non-competitive RT inhibitors with respect to either dNTP or nucleic acid substrates and block DNA synthesis by binding to a hydrophobic pocket of RT [9-15]. "
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    ABSTRACT: The K65R substitution in human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) is the major resistance mutation selected in patients treated with first-line antiretroviral tenofovir disoproxil fumarate (TDF).4'-ethynyl-2-fluoro-2'-deoxyadenosine (EFdA), is the most potent nucleoside analog RT inhibitor (NRTI) that unlike all approved NRTIs retains a 3'-hydroxyl group and has remarkable potency against wild-type (WT) and drug-resistant HIVs. EFdA acts primarily as a chain terminator by blocking translocation following its incorporation into the nascent DNA chain. EFdA is in preclinical development and its effect on clinically relevant drug resistant HIV strains is critically important for the design of optimal regimens prior to initiation of clinical trials. Here we report that the K65R RT mutation causes hypersusceptibility to EFdA. Specifically, in single replication cycle experiments we found that EFdA blocks WT HIV ten times more efficiently than TDF. Under the same conditions K65R HIV was inhibited over 70 times more efficiently by EFdA than TDF. We determined the molecular mechanism of this hypersensitivity using enzymatic studies with WT and K65R RT. This substitution causes minor changes in the efficiency of EFdA incorporation with respect to the natural dATP substrate and also in the efficiency of RT translocation following incorporation of the inhibitor into the nascent DNA. However, a significant decrease in the excision efficiency of EFdA-MP from the 3' primer terminus appears to be the primary cause of increased susceptibility to the inhibitor. Notably, the effects of the mutation are DNA-sequence dependent. We have elucidated the mechanism of K65R HIV hypersusceptibility to EFdA. Our findings highlight the potential of EFdA to improve combination strategies against TDF-resistant HIV-1 strains.
    Retrovirology 06/2013; 10(1):65. DOI:10.1186/1742-4690-10-65 · 4.19 Impact Factor
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    • "As ploymerization proceeds, RNase H activity degrades RNA of the RNA/DNA replication intermediates [21]. Although RNase H activity and its interplay with polymerase activity have well-documented [22] [23], it remains unclear how RT–RNase H distinguishes between RNA/DNA hybrid and the structurally similar RNA/RNA homoduplex. For model simplification and specific functional characterizations of IN–RT interactions, we have not involved the documented interplay between RT-polymerase and RNase H activities. "
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    ABSTRACT: Human immunodeficiency virus (HIV) infection yields a high level of non-integrated viral DNA in the infected cells and up to 99% of total viral DNA can be capable of transcription. This capability of non-integrated viral DNA is reducing the efficacy of anti-HIV drug development approaches that solely focus on the integration reactions of viral replication. Using kinetic modeling, we show the transient coordinated regulation of viral DNA production by retrovirus-encoded interacting enzymes reverse transcriptase (RT) and integrase (IN), and thus we identify a possible mechanism for reducing overall efficiency of viral replication. The results indicate that both IN.RT and IN.DNA complexes and their formation rates affect RT processivity and thereby the viral DNA expression level within the pre-integration complex.
    FEBS letters 12/2012; 587(5). DOI:10.1016/j.febslet.2012.12.007 · 3.17 Impact Factor
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    • "Reverse transcription and reverse transcriptases All retroviruses, as well as retrotransposons, undergo a unique DNA synthesis process called reverse transcription, which converts single stranded RNA genomes into double stranded DNA. This process is catalyzed by virally encoded DNA polymerases, reverse transcriptases (RT) (reviewed in Hu and Hughes, 2012; Sarafianos et al., 2009). Unlike cellular DNA polymerases, which synthesize DNA from DNA templates, RTs can execute DNA polymerization from RNA templates as well. "
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    ABSTRACT: Retroviruses consume cellular deoxynucleoside triphosphates (dNTPs) to convert their RNA genomes into proviral DNA through reverse transcription. While all retroviruses replicate in dividing cells, lentiviruses uniquely replicate in nondividing cells such as macrophages. Importantly, dNTP levels in nondividing cells are extremely low, compared to dividing cells. Indeed, a recently discovered anti-HIV/SIV restriction factor, SAMHD1, which is a dNTP triphosphohydrolase, is responsible for the limited dNTP pool of nondividing cells. Lentiviral reverse transcriptases (RT) uniquely stay functional even at the low dNTP concentrations in nondividing cells. Interestingly, Vpx of HIV-2/SIVsm proteosomally degrades SAMHD1, which elevates cellular dNTP pools and accelerates lentiviral replication in nondividing cells. These Vpx-encoding lentiviruses rapidly replicate in nondividing cells by encoding both highly functional RTs and Vpx. Here, we discuss a series of mechanistic and virological studies that have contributed to conceptually linking cellular dNTP levels and the adaptation of lentiviral replication in nondividing cells.
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