Reply to "Structural requirements for RNA degradation by HIV-1 reverse transcriptase".
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ABSTRACT:
SUBMITTER: Lapkouski M
PROVIDER: S-EPMC4207619 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Recent X-ray crystal structure determinations of Moloney murine leukemia virus reverse transcriptase (MoMLV RT) have allowed for more accurate structure/function comparisons to HIV-1 RT than were formerly possible. Previous biochemical studies of MoMLV RT in conjunction with knowledge of sequence homologies to HIV-1 RT and overall fold similarities to RTs in general, provided a foundation upon which to build. In addition, numerous crystal structures of the MoMLV RT fingers/palm subdomain had also shed light on one of the critical functions of the enzyme, specifically polymerization. Now in the advent of new structural information, more intricate examination of MoMLV RT in its entirety can be realized, and thus the comparisons with HIV-1 RT may be more critically elucidated. Here, we will review the similarities and differences between MoMLV RT and HIV-1 RT via structural analysis, and propose working models for the MoMLV RT based upon that information.
| S-EPMC2443788 | biostudies-literature
Project description:We previously proposed that mutations in the connection subdomain (cn) of HIV-1 reverse transcriptase increase AZT resistance by altering the balance between nucleotide excision and template RNA degradation. To test the predictions of this model, we analyzed the effects of previously identified cn mutations in combination with thymidine analog mutations (D67N, K70R, T215Y, and K219Q) on in vitro RNase H activity and AZT monophosphate (AZTMP) excision. We found that cn mutations G335C/D, N348I, A360I/V, V365I, and A376S decreased primary and secondary RNase H cleavages. The patient-derived cns increased ATP- and PPi-mediated AZTMP excision on an RNA template compared with a DNA template. One of 5 cns caused an increase in ATP-mediated AZTMP excision on a DNA template, whereas three cns showed a higher ratio of ATP- to PPi-mediated excision, indicating that some cn mutations also affect excision on a DNA substrate. Overall, the results strongly support the model that cn mutations increase AZT resistance by reducing template RNA degradation, thereby providing additional time for RT to excise AZTMP.
| S-EPMC2491488 | biostudies-literature
Project description:Crystal structures and simulations suggest that conformational changes are critical for the function of HIV-1 reverse transcriptase. The enzyme is an asymmetric heterodimer of two subunits, p66 and p51. The two subunits have the same N-terminal sequence, with the p51 subunit lacking the C-terminal RNase H domain. We used hydrogen exchange mass spectrometry to probe the structural dynamics of RT. H/D exchange revealed that the fingers and palm subdomains of both subunits form the stable core of the heterodimer. In the crystal structure, the tertiary fold of the p51 subunit is more compact than that of the polymerase domain of the p66 subunit, yet both subunits show similar flexibility. The p66 subunit contains the polymerase and RNase H catalytic sites. H/D exchange indicated that the RNase H domain of p66 is very flexible. The beta-sheet beta12-beta13-beta14 lies at the base of the thumb subdomain of p66 and contains highly conserved residues involved in template/primer binding and NNRTI binding. Using the unique ability of hydrogen exchange mass spectrometry to resolve slowly interconverting species, we found that beta-sheet beta12-beta13-beta14 undergoes slow cooperative unfolding with a t(1/2) of <20 s. The H/D exchange results are discussed in relation to existing structural, simulation, and sequence information.
| S-EPMC2814253 | biostudies-literature
Project description:Formation of active HIV-1 reverse transcriptase (RT) proceeds via a structural maturation process that involves subdomain rearrangements and formation of an asymmetric p66/p66' homodimer. These studies were undertaken to evaluate whether the information about this maturation process can be used to identify small molecule ligands that retard or interfere with the steps involved. We utilized the isolated polymerase domain, p51, rather than p66, since the initial subdomain rearrangements are largely limited to this domain. Target sites at subdomain interfaces were identified and computational analysis used to obtain an initial set of ligands for screening. Chromatographic evaluations of the p51 homodimer/monomer ratio support the feasibility of this approach. Ligands that bind near the interfaces and a ligand that binds directly to a region of the fingers subdomain involved in subunit interface formation were identified, and the interactions were further characterized by NMR spectroscopy and X-ray crystallography. Although these ligands were found to reduce dimer formation, further efforts will be required to obtain ligands with higher binding affinity. In contrast with previous ligand identification studies performed on the RT heterodimer, subunit interface surfaces are solvent-accessible in the p51 and p66 monomers, making these constructs preferable for identification of ligands that directly interfere with dimerization.
| S-EPMC10669680 | biostudies-literature
Project description:Systematic evolution of ligands through exponential enrichment (SELEX) is a well-established method for generating nucleic acid populations that are enriched for specified functions. High-throughput sequencing (HTS) enhances the power of comparative sequence analysis to reveal details of how RNAs within these populations recognize their targets. We used HTS analysis to evaluate RNA populations selected to bind type I human immunodeficiency virus reverse transcriptase (RT). The populations are enriched in RNAs of independent lineages that converge on shared motifs and in clusters of RNAs with nearly identical sequences that share common ancestry. Both of these features informed inferences of the secondary structures of enriched RNAs, their minimal structural requirements and their stabilities in RT-aptamer complexes. Monitoring population dynamics in response to increasing selection pressure revealed RNA inhibitors of RT that are more potent than the previously identified pseudoknots. Improved potency was observed for inhibition of both purified RT in enzymatic assays and viral replication in cell-based assays. Structural and functional details of converged motifs that are obscured by simple consensus descriptions are also revealed by the HTS analysis. The approach presented here can readily be generalized for the efficient and systematic post-SELEX development of aptamers for down-stream applications.
| S-EPMC3561961 | biostudies-literature
Project description:HIV-1 reverse transcriptase (RT) contains both DNA polymerase and RNase H activities to convert the viral genomic RNA to dsDNA in infected host cells. Here we report the 2.65-Å resolution structure of HIV-1 RT engaging in cleaving RNA in an RNA/DNA hybrid. A preferred substrate sequence is absolutely required to enable the RNA/DNA hybrid to adopt the distorted conformation needed to interact properly with the RNase H active site in RT. Substituting two nucleotides 4 bp upstream from the cleavage site results in scissile-phosphate displacement by 4 Å. We also have determined the structure of HIV-1 RT complexed with an RNase H-resistant polypurine tract sequence, which adopts a rigid structure and is accommodated outside of the nuclease active site. Based on this newly gained structural information and a virtual drug screen, we have identified an inhibitor specific for the viral RNase H but not for its cellular homologs.
| S-EPMC5777007 | biostudies-literature
Project description:Efavirenz is a second-generation nonnucleoside reverse transcriptase inhibitor (NNRTI) and a common component of clinically approved anti-AIDS regimens. NNRTIs are noncompetitive inhibitors that bind in a hydrophobic pocket in the p66 subunit of reverse transcriptase (RT) ?10 Å from the polymerase active site. Hydrogen exchange mass spectrometry (HXMS) shows that efavirenz binding reduces molecular flexibility in multiple regions of RT heterodimer in addition to the NNRTI binding site. Of the 47 peptic fragments monitored by HXMS, 15 showed significantly altered H/D exchange rates in the presence of efavirenz. The slow cooperative unfolding of a ?-sheet in the NNRTI binding pocket, which was previously observed in unliganded RT, is dramatically suppressed by efavirenz. HXMS also defines an extensive network of allosterically coupled sites, including four distinct regions of allosteric stabilization, and one region of allosteric destabilization. The effects of efavirenz binding extend > 60 Å from the NNRTI binding pocket. Allosteric changes to the structural dynamics propagate to the thumb and connection subdomains and RNase H domain of the p66 subunit as well as the thumb and palm subdomains of the p51 subunit. These allosteric regions may represent potential new drug targets.
| S-EPMC3010017 | biostudies-literature
Project description:The reverse transcriptase (RT) enzyme is the prime target of nucleoside/ nucleotide (NRTI) and non-nucleoside (NNRTI) reverse transcriptase inhibitors. Here we investigate the structural basis of effects of drug-resistance mutations in clade C RT using three-dimensional structural modeling. Apropos the expectation was for unique mechanisms in clade C based on interactions with amino acids of p66 subunit in RT molecule. 3-D structures of RT with mutations found in sequences from 2 treatment naïve, 8 failed and one reference clade C have been modeled and analyzed. Models were generated by computational mutation of available crystal structures of drug bound homologous RT. Energy minimization of the models and the structural analyses were carried out using standard methods. Mutations at positions 75,101,118,190,230,238 and 318 known to confer drug resistance were investigated. Different mutations produced different effects such as alteration of geometry of the drug-binding pocket, structural changes at the site of entry of the drug (into the active site), repositioning the template bases or by discriminating the inhibitors from their natural substrates. For the mutations analyzed, NRTI resistance was mediated mainly by the ability to discriminate between inhibitors and natural substrate, whereas, NNRTI resistance affected either the drug entry or the geometry of the active site. Our analysis suggests that different mutations result in different structural effects affecting the ability of a given drug to bind to the RT. Our studies will help in the development of newer drugs taking into account the presence of these mutations and the structural basis of drug resistance.
| S-EPMC2770369 | biostudies-literature
Project description:The mature form of reverse transcriptase (RT) is a heterodimer comprising the intact 66-kDa subunit (p66) and a smaller 51-kDa subunit (p51) that is generated by removal of most of the RNase H (RNH) domain from a p66 subunit by proteolytic cleavage between residues 440 and 441. Viral infectivity is eliminated by mutations such as F440A and E438N in the proteolytic cleavage sequence, while normal processing and virus infectivity are restored by a compensatory mutation, T477A, that is located more than 10 Å away from the processing site. The molecular basis for this compensatory effect has remained unclear. We therefore investigated structural characteristics of RNH mutants using computational and experimental approaches. Our Nuclear Magnetic Resonance and Differential Scanning Fluorimetry results show that both F440A and E438N mutations disrupt RNH folding. Addition of the T477A mutation restores correct folding of the RNH domain despite the presence of the F440A or E438N mutations. Molecular dynamics simulations suggest that the T477A mutation affects the processing site by altering relative orientations of secondary structure elements. Predictions of sequence tolerance suggest that phenylalanine and tyrosine are structurally preferred at residues 440 and 441, respectively, which are the P1 and P1' substrate residues known to require bulky side chains for substrate specificity. Interestingly, our study demonstrates that the processing site residues, which are critical for protease substrate specificity and must be exposed to the solvent for efficient processing, also function to maintain proper RNH folding in the p66/p51 heterodimer.
| S-EPMC4509971 | biostudies-literature
Project description:HIV-1 Reverse Transcriptase (HIV-1 RT) has been the target of numerous approved anti-AIDS drugs that are key components of Highly Active Anti-Retroviral Therapies (HAART). It remains the target of extensive structural studies that continue unabated for almost twenty years. The crystal structures of wild-type or drug-resistant mutant HIV RTs in the unliganded form or in complex with substrates and/or drugs have offered valuable glimpses into the enzyme's folding and its interactions with DNA and dNTP substrates, as well as with nucleos(t)ide reverse transcriptase inhibitor (NRTI) and non-nucleoside reverse transcriptase inhibitor (NNRTIs) drugs. These studies have been used to interpret a large body of biochemical results and have paved the way for innovative biochemical experiments designed to elucidate the mechanisms of catalysis and drug inhibition of polymerase and RNase H functions of RT. In turn, the combined use of structural biology and biochemical approaches has led to the discovery of novel mechanisms of drug resistance and has contributed to the design of new drugs with improved potency and ability to suppress multi-drug resistant strains.
| S-EPMC2850067 | biostudies-literature