1
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Ito Y, Lu H, Kitajima M, Ishikawa H, Nakata Y, Iwatani Y, Hoshino T. Sticklac-Derived Natural Compounds Inhibiting RNase H Activity of HIV-1 Reverse Transcriptase. JOURNAL OF NATURAL PRODUCTS 2023; 86:2487-2495. [PMID: 37874155 DOI: 10.1021/acs.jnatprod.3c00662] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2023]
Abstract
The emergence of drug-resistant viruses is a serious concern in current chemotherapy for human immunodeficiency virus type-1 (HIV-1) infectious diseases. Hence, antiviral drugs aiming at targets that are different from those of approved drugs are still required, and the RNase H activity of HIV-1 reverse transcriptase is a suitable target. In this study, a search of a series of natural compounds was performed to identify the RNase H inhibitors. Three compounds were found to block the RNase H enzymatic activity. A laccaic acid skeleton was observed in all three natural compounds. A hydroxy phenyl group is connected to an anthraquinone backbone in the skeleton. An acetamido-ethyl, amino-carboxy-ethyl, and amino-ethyl are bound to the phenyl in laccaic acids A, C, and E, respectively. Laccaic acid C showed a 50% inhibitory concentration at 8.1 μM. Laccaic acid C also showed inhibitory activity in a cell-based viral proliferation assay. Binding structures of these three laccaic acids were determined by X-ray crystallographic analysis using a recombinant protein composed of the HIV-1 RNase H domain. Two divalent metal ions were located at the catalytic center in which one carbonyl and two hydroxy groups on the anthraquinone backbone chelated two metal ions. Molecular dynamics simulations were performed to examine the stabilities of the binding structures. Laccaic acid C showed the strongest binding to the catalytic site. These findings will be helpful for the design of potent inhibitors with modification of laccaic acids to enhance the binding affinity.
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Affiliation(s)
- Yuma Ito
- Laboratory of Molecular Design, Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8675, Japan
| | - Huiyan Lu
- Laboratory of Molecular Design, Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8675, Japan
| | - Mariko Kitajima
- Laboratory of Middle Molecular Chemistry, Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8675, Japan
| | - Hayato Ishikawa
- Laboratory of Middle Molecular Chemistry, Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8675, Japan
| | - Yoshihiro Nakata
- Department of Infectious Diseases and Immunology, Clinical Research Center, National Hospital Organization Nagoya Medical Center, 4-1-1 Sannomaru, Naka-ku, Nagoya, Aichi 460-0001, Japan
| | - Yasumasa Iwatani
- Department of Infectious Diseases and Immunology, Clinical Research Center, National Hospital Organization Nagoya Medical Center, 4-1-1 Sannomaru, Naka-ku, Nagoya, Aichi 460-0001, Japan
- Department of AIDS Research, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya, Aichi 466-8550, Japan
| | - Tyuji Hoshino
- Laboratory of Molecular Design, Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8675, Japan
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2
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Ilina TV, Brosenitsch T, Sluis-Cremer N, Ishima R. Retroviral RNase H: Structure, mechanism, and inhibition. Enzymes 2021; 50:227-247. [PMID: 34861939 DOI: 10.1016/bs.enz.2021.07.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
All retroviruses encode the enzyme, reverse transcriptase (RT), which is involved in the conversion of the single-stranded viral RNA genome into double-stranded DNA. RT is a multifunctional enzyme and exhibits DNA polymerase and ribonuclease H (RNH) activities, both of which are essential to the reverse-transcription process. Despite the successful development of polymerase-targeting antiviral drugs over the last three decades, no bona fide inhibitor against the RNH activity of HIV-1 RT has progressed to clinical evaluation. In this review article, we describe the retroviral RNH function and inhibition, with primary consideration of the structural aspects of inhibition.
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Affiliation(s)
- Tatiana V Ilina
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
| | - Teresa Brosenitsch
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
| | - Nicolas Sluis-Cremer
- Department of Medicine, Division of Infectious Diseases, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
| | - Rieko Ishima
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States.
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3
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Wang R, Belew AT, Achuthan V, El Sayed N, DeStefano JJ. Physiological magnesium concentrations increase fidelity of diverse reverse transcriptases from HIV-1, HIV-2, and foamy virus, but not MuLV or AMV. J Gen Virol 2021; 102. [PMID: 34904939 PMCID: PMC10019084 DOI: 10.1099/jgv.0.001708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Accepted: 11/05/2021] [Indexed: 11/18/2022] Open
Abstract
Reverse transcriptases (RTs) are typically assayed using optimized Mg2+ concentrations (~5-10 mM) several-fold higher than physiological cellular free Mg2+ (~0.5 mM). Recent analyses demonstrated that HIV-1, but not Moloney murine leukaemia (MuLV) or avain myeloblastosis (AMV) virus RTs has higher fidelity in low Mg2+. In the current report, lacZα-based α-complementation assays were used to measure the fidelity of several RTs including HIV-1 (subtype B and A/E), several drug-resistant HIV-1 derivatives, HIV-2, and prototype foamy virus (PFV), all which showed higher fidelity using physiological Mg2+, while MuLV and AMV RTs demonstrated equivalent fidelity in low and high Mg2+. In 0.5 mM Mg2+, all RTs demonstrated approximately equal fidelity, except for PFV which showed higher fidelity. A Next Generation Sequencing (NGS) approach that used barcoding to determine mutation profiles was used to examine the types of mutations made by HIV-1 RT (type B) in low (0.5 mM) and high (6 mM) Mg2+ on a lacZα template. Unlike α-complementation assays which are dependent on LacZα activity, the NGS assay scores mutations at all positions and of every type. Consistent with α-complementation assays, a ~four-fold increase in mutations was observed in high Mg2+. These findings help explain why HIV-1 RT displays lower fidelity in vitro (with high Mg2+ concentrations) than other RTs (e.g. MuLV and AMV), yet cellular fidelity for these viruses is comparable. Establishing in vitro conditions that accurately represent RT's activity in cells is pivotal to determining the contribution of RT and other factors to the mutation profile observed with HIV-1.
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Affiliation(s)
- Ruofan Wang
- Department of Cell Biology and Molecular Genetics, Bioscience Research Building, University of Maryland, College Park, Maryland 20742, USA
- Present address: Vigene Biosciences, Rockville Maryland, USA
| | - Ashton T Belew
- Department of Cell Biology and Molecular Genetics, Bioscience Research Building, University of Maryland, College Park, Maryland 20742, USA
| | - Vasudevan Achuthan
- Department of Cell Biology and Molecular Genetics, Bioscience Research Building, University of Maryland, College Park, Maryland 20742, USA
- Present address: CRISPR Therapeutics, Cambridge, Massachusetts, USA
| | - Najib El Sayed
- Department of Cell Biology and Molecular Genetics, Bioscience Research Building, University of Maryland, College Park, Maryland 20742, USA
- Maryland Pathogen Research Institute, College Park, Maryland, USA
| | - Jeffrey J DeStefano
- Department of Cell Biology and Molecular Genetics, Bioscience Research Building, University of Maryland, College Park, Maryland 20742, USA
- Maryland Pathogen Research Institute, College Park, Maryland, USA
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4
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Cilento ME, Kirby KA, Sarafianos SG. Avoiding Drug Resistance in HIV Reverse Transcriptase. Chem Rev 2021; 121:3271-3296. [PMID: 33507067 DOI: 10.1021/acs.chemrev.0c00967] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
HIV reverse transcriptase (RT) is an enzyme that plays a major role in the replication cycle of HIV and has been a key target of anti-HIV drug development efforts. Because of the high genetic diversity of the virus, mutations in RT can impart resistance to various RT inhibitors. As the prevalence of drug resistance mutations is on the rise, it is necessary to design strategies that will lead to drugs less susceptible to resistance. Here we provide an in-depth review of HIV reverse transcriptase, current RT inhibitors, novel RT inhibitors, and mechanisms of drug resistance. We also present novel strategies that can be useful to overcome RT's ability to escape therapies through drug resistance. While resistance may not be completely avoidable, designing drugs based on the strategies and principles discussed in this review could decrease the prevalence of drug resistance.
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Affiliation(s)
- Maria E Cilento
- Laboratory of Biochemical Pharmacology, Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia 30322, United States.,Children's Healthcare of Atlanta, Atlanta, Georgia 30307, United States
| | - Karen A Kirby
- Laboratory of Biochemical Pharmacology, Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia 30322, United States.,Children's Healthcare of Atlanta, Atlanta, Georgia 30307, United States
| | - Stefan G Sarafianos
- Laboratory of Biochemical Pharmacology, Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia 30322, United States.,Children's Healthcare of Atlanta, Atlanta, Georgia 30307, United States
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5
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Gong S, Kirmizialtin S, Chang A, Mayfield JE, Zhang YJ, Johnson KA. Kinetic and thermodynamic analysis defines roles for two metal ions in DNA polymerase specificity and catalysis. J Biol Chem 2020; 296:100184. [PMID: 33310704 PMCID: PMC7948414 DOI: 10.1074/jbc.ra120.016489] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2020] [Revised: 12/05/2020] [Accepted: 12/11/2020] [Indexed: 11/06/2022] Open
Abstract
Magnesium ions play a critical role in catalysis by many enzymes and contribute to the fidelity of DNA polymerases through a two-metal ion mechanism. However, specificity is a kinetic phenomenon and the roles of Mg2+ ions in each step in the catalysis have not been resolved. We first examined the roles of Mg2+ by kinetic analysis of single nucleotide incorporation catalyzed by HIV reverse transcriptase. We show that Mg.dNTP binding induces an enzyme conformational change at a rate that is independent of free Mg2+ concentration. Subsequently, the second Mg2+ binds to the closed state of the enzyme-DNA-Mg.dNTP complex (Kd = 3.7 mM) to facilitate catalysis. Weak binding of the catalytic Mg2+ contributes to fidelity by sampling the correctly aligned substrate without perturbing the equilibrium for nucleotide binding at physiological Mg2+ concentrations. An increase of the Mg2+ concentration from 0.25 to 10 mM increases nucleotide specificity (kcat/Km) 12-fold largely by increasing the rate of the chemistry relative to the rate of nucleotide release. Mg2+ binds very weakly (Kd ≤ 37 mM) to the open state of the enzyme. Analysis of published crystal structures showed that HIV reverse transcriptase binds only two metal ions prior to incorporation of a correct base pair. Molecular dynamics simulations support the two-metal ion mechanism and the kinetic data indicating weak binding of the catalytic Mg2+. Molecular dynamics simulations also revealed the importance of the divalent cation cloud surrounding exposed phosphates on the DNA. These results enlighten the roles of the two metal ions in the specificity of DNA polymerases.
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Affiliation(s)
- Shanzhong Gong
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas, USA
| | - Serdal Kirmizialtin
- Chemistry Program, Science Division, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
| | - Adrienne Chang
- Chemistry Program, Science Division, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
| | - Joshua E Mayfield
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas, USA
| | - Yan Jessie Zhang
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas, USA
| | - Kenneth A Johnson
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas, USA.
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6
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Xi Z, Wang Z, Sarafianos SG, Myshakina NS, Ishima R. Determinants of Active-Site Inhibitor Interaction with HIV-1 RNase H. ACS Infect Dis 2019; 5:1963-1974. [PMID: 31577424 DOI: 10.1021/acsinfecdis.9b00300] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The ribonuclease H (RNH) activity of HIV-1 reverse transcriptase (RT) is essential for viral replication and can be a target for drug development. Yet, no RNH inhibitor to date has substantial antiviral activity to allow advancement into clinical development. Herein, we describe our characterization of the detailed binding mechanisms of RNH active-site inhibitors, YLC2-155 and ZW566, that bind to the RNH domain through divalent metal ions, using NMR, molecular docking, and quantum mechanical calculations. In the presence of Mg2+, NMR spectra of RNH exhibited split (two) resonances for some residues upon inhibitor binding, suggesting two binding modes, an observation consistent with the docking results. The relative populations of the two binding conformers were independent of inhibitor or Mg2+ concentration, with one conformation consistently more favored. In our docking study, one distinctive pose of ZW566 showed more interactions with surrounding residues of RNH compared to the analogous binding pose of YLC2-155. Inhibitor titration experiments revealed a lower dissociation constant for ZW566 compared to YLC2-155, in agreement with its higher inhibitory activity. Mg2+ titration data also indicated a stronger dependence on Mg2+ for the RNH interaction with ZW566 compared to YLC2-155. Combined docking and quantum mechanical calculation results suggest that stronger metal coordination as well as more protein-inhibitor interactions may account for the higher binding affinity of ZW566. These findings support the idea that strategies for the development of potent competitive active site RNH inhibitors should take into account not only metal-inhibitor coordination but also protein-inhibitor interaction and conformational selectivity.
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Affiliation(s)
- Zhaoyong Xi
- Department of Structural Biology, University of Pittsburgh School of Medicine, 3501 Fifth Avenue, Pittsburgh, Pennsylvania 15260, United States
| | - Zhengqiang Wang
- Center for Drug Design, College of Pharmacy, University of Minnesota, 516 Delaware Street SE, PWB 7-215,
MMC 204, Minneapolis, Minnesota 55455, United States
| | - Stefan G. Sarafianos
- Laboratory of Biochemical Pharmacology, Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia 30322, United States
| | - Nataliya S. Myshakina
- Department of Natural Science, Chatham University, Woodland Road, Pittsburgh, Pennsylvania 15232, United States
| | - Rieko Ishima
- Department of Structural Biology, University of Pittsburgh School of Medicine, 3501 Fifth Avenue, Pittsburgh, Pennsylvania 15260, United States
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7
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DeStefano JJ. Non-nucleoside Reverse Transcriptase Inhibitors Inhibit Reverse Transcriptase through a Mutually Exclusive Interaction with Divalent Cation-dNTP Complexes. Biochemistry 2019; 58:2176-2187. [PMID: 30900874 DOI: 10.1021/acs.biochem.9b00028] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Non-nucleoside reverse transcriptase inhibitors (NNRTIs) are considered noncompetitive inhibitors that structurally alter reverse transcriptase (RT) and dramatically decrease catalysis. In this report, biochemical analysis with various divalent cations was used to demonstrate that NNRTIs and divalent cation-dNTP complexes are mutually exclusive, inhibiting each other's binding to RT/primer/template (RT-P/T) complexes. The binding of catalytically competent divalent cation-dNTP complexes to RT-P/T was measured with Mg2+, Mn2+, Zn2+, Co2+, and Ni2+ using Ca2+, a noncatalytic cation, for displacement. Binding strength order was Mn2+ ≈ Zn2+ ≫ Co2+ > Mg2+ ≈ Ni2+. Consistent with but not exclusive to mutually exclusive binding, primer extension assays showed that stronger divalent cation-dNTP complexes were more resistant to NNRTIs (efavirenz (EFV), rilpivirine (RPV), and nevirapine (NVP)). Filtration assays demonstrated that divalent cation-dNTP complexes inhibited the binding of 14C-labeled EFV to RT-P/T with stronger binding complexes formed with Mn2+ inhibiting more potently than those with Mg2+. Conversely, filter binding assays demonstrated that EFV inhibited 3H-labeled dNTP binding to RT-P/T complexes with displacement of Mn2+-dNTP complexes requiring much greater concentrations of EFV than the more weakly bound Mg2+-dNTP complexes. EFV bound relatively weakly to the NNRTI resistant K103N RT; but, binding was modestly enhanced in the presence of P/T, and EFV was easily displaced by divalent cation-dNTP complexes. This suggests that K103N overcomes EFV inhibition mostly by binding more weakly to the drug and is in contrast to other reports that indicate K103N has little to no effect on drug or dNTP binding. Overall, this biochemical analysis supports recent biophysical analyses of NNRTI-RT interactions that indicate mutually exclusive binding.
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Affiliation(s)
- Jeffrey J DeStefano
- Department of Cell Biology and Molecular Genetics and the Maryland Pathogen Research Institute , University of Maryland , College Park , Maryland 20742 , United States
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8
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Oda M, Xi Z, Inaba S, Slack RL, Ishima R. Binding thermodynamics of metal ions to HIV-1 ribonuclease H domain. JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY 2019; 135:2647-2653. [PMID: 30853849 PMCID: PMC6402781 DOI: 10.1007/s10973-018-7445-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 05/27/2018] [Indexed: 06/09/2023]
Abstract
Metal-protein interactions are not necessarily tight in many transient biological processes, such as cellular signaling, enzyme regulation, and molecular recognition. Here, we analyzed the binding thermodynamics and characterized the structural effect of divalent metal ions, i.e. Mn2+, Zn2+, and Mg2+, to the isolated ribonuclease H (RNH) of human immunodeficiency virus (HIV) using isothermal titration calorimetry (ITC) and circular dichroism. The binding thermodynamics of Mg2+ to RNH was determined using competition ITC experiments, and the binding affinity of Mg2+ was found to be about 40- and 400-times lower than those of Mn2+ and of Zn2+, respectively. The structural analysis showed that Mg2+ binding had little effect on the thermal stability of RNH, while Zn2+ and Mn2+ binding increased the stability. The thermodynamic characteristics of RNH metal binding, compared to intact HIV reverse transcriptase, and a possible mechanism of conformational change induced upon metal ion binding, in correlation with the structure-function relationship, are discussed.
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Affiliation(s)
- Masayuki Oda
- Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, 1-5 Hangi-cho, Shimogamo, Sakyo-ku, Kyoto, Kyoto 606-8522, Japan
| | - Zhaoyong Xi
- Department of Structural Biology, University of Pittsburgh School of, Medicine, Pittsburgh, Pennsylvania 15260, United States
| | - Satomi Inaba
- Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, 1-5 Hangi-cho, Shimogamo, Sakyo-ku, Kyoto, Kyoto 606-8522, Japan
- Research & Utilization Division, Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo, Hyogo 679-5198, Japan
| | - Ryan L. Slack
- Department of Structural Biology, University of Pittsburgh School of, Medicine, Pittsburgh, Pennsylvania 15260, United States
| | - Rieko Ishima
- Department of Structural Biology, University of Pittsburgh School of, Medicine, Pittsburgh, Pennsylvania 15260, United States
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9
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Achuthan V, Singh K, DeStefano JJ. Physiological Mg 2+ Conditions Significantly Alter the Inhibition of HIV-1 and HIV-2 Reverse Transcriptases by Nucleoside and Non-Nucleoside Inhibitors in Vitro. Biochemistry 2016; 56:33-46. [PMID: 27936595 DOI: 10.1021/acs.biochem.6b00943] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Reverse transcriptases (RTs) are typically assayed in vitro with 5-10 mM Mg2+, whereas the free Mg2+ concentration in cells is much lower. Artificially high Mg2+ concentrations used in vitro can misrepresent different properties of human immunodeficiency virus (HIV) RT, including fidelity, catalysis, pausing, and RNase H activity. Here, we analyzed nucleoside (NRTIs) and non-nucleoside RT inhibitors (NNRTIs) in primer extension assays at different concentrations of free Mg2+. At low concentrations of Mg2+, NRTIs and dideoxynucleotides (AZTTP, ddCTP, ddGTP, and 3TCTP) inhibited HIV-1 and HIV-2 RT synthesis less efficiently than they did with large amounts of Mg2+, whereas inhibition by the "translocation-defective RT inhibitor" EFdA (4'-ethynyl-2-fluoro-2'-deoxyadenosine) was unaffected by Mg2+ concentrations. Steady-state kinetic analyses revealed that the reduced level of inhibition at low Mg2+ concentrations resulted from a 3-9-fold (depending on the particular nucleotide and inhibitor) less efficient incorporation (based on kcat/Km) of these NRTIs under this condition compared to incorporation of natural dNTPs. In contrast, EFdATP was incorporated with an efficiency similar to that of its analogue dATP at low Mg2+ concentrations. Unlike NRTIs, NNRTIs (nevirapine, efavirenz, and rilviripine), were approximately 4-fold (based on IC50 values) more effective at low than at high Mg2+ concentrations. Drug-resistant HIV-1 RT mutants also displayed the Mg2+-dependent difference in susceptibility to NRTIs and NNRTIs. In summary, analyzing the efficiency of inhibitors under more physiologically relevant low-Mg2+ conditions yielded results dramatically different from those from measurements using commonly employed high-Mg2+ in vitro conditions. These results also emphasize differences in Mg2+ sensitivity between the translocation inhibitor EFdATP and other NRTIs.
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Affiliation(s)
- Vasudevan Achuthan
- Cell Biology and Molecular Genetics, University of Maryland , College Park, Maryland 20742, United States.,Maryland Pathogen Research Institute , College Park, Maryland 20742, United States
| | - Kamlendra Singh
- Christopher S. Bond Life Sciences Center, University of Missouri , Columbia, Missouri 65211, United States.,Department of Molecular Microbiology and Immunology, University of Missouri School of Medicine , Columbia, Missouri 65211, United States
| | - Jeffrey J DeStefano
- Cell Biology and Molecular Genetics, University of Maryland , College Park, Maryland 20742, United States.,Maryland Pathogen Research Institute , College Park, Maryland 20742, United States
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10
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Karki I, Christen MT, Spiriti J, Slack RL, Oda M, Kanaori K, Zuckerman DM, Ishima R. Entire-Dataset Analysis of NMR Fast-Exchange Titration Spectra: A Mg 2+ Titration Analysis for HIV-1 Ribonuclease H Domain. J Phys Chem B 2016; 120:12420-12431. [PMID: 27973819 DOI: 10.1021/acs.jpcb.6b08323] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This article communicates our study to elucidate the molecular determinants of weak Mg2+ interaction with the ribonuclease H (RNH) domain of HIV-1 reverse transcriptase in solution. As the interaction is weak (a ligand-dissociation constant >1 mM), nonspecific Mg2+ interaction with the protein or interaction of the protein with other solutes that are present in the buffer solution can confound the observed Mg2+-titration data. To investigate these indirect effects, we monitored changes in the chemical shifts of backbone amides of RNH by recording NMR 1H-15N heteronuclear single-quantum coherence spectra upon titration of Mg2+ into an RNH solution. We performed the titration under three different conditions: (1) in the absence of NaCl, (2) in the presence of 50 mM NaCl, and (3) at a constant 160 mM Cl- concentration. Careful analysis of these three sets of titration data, along with molecular dynamics simulation data of RNH with Na+ and Cl- ions, demonstrates two characteristic phenomena distinct from the specific Mg2+ interaction with the active site: (1) weak interaction of Mg2+, as a salt, with the substrate-handle region of the protein and (2) overall apparent lower Mg2+ affinity in the absence of NaCl compared to that in the presence of 50 mM NaCl. A possible explanation may be that the titrated MgCl2 is consumed as a salt and interacts with RNH in the absence of NaCl. In addition, our data suggest that Na+ increases the kinetic rate of the specific Mg2+ interaction at the active site of RNH. Taken together, our study provides biophysical insight into the mechanism of weak metal interaction on a protein.
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Affiliation(s)
- Ichhuk Karki
- Department of Structural Biology and ‡Department of Computational and Systems Biology, University of Pittsburgh School of Medicine , Pittsburgh, Pennsylvania 15260, United States.,Graduate School of Life and Environmental Sciences, Kyoto Prefectural University and ⊥Department of Biomolecular Engineering, Kyoto Institute of Technology , Kyoto 606, Japan
| | - Martin T Christen
- Department of Structural Biology and ‡Department of Computational and Systems Biology, University of Pittsburgh School of Medicine , Pittsburgh, Pennsylvania 15260, United States.,Graduate School of Life and Environmental Sciences, Kyoto Prefectural University and ⊥Department of Biomolecular Engineering, Kyoto Institute of Technology , Kyoto 606, Japan
| | - Justin Spiriti
- Department of Structural Biology and ‡Department of Computational and Systems Biology, University of Pittsburgh School of Medicine , Pittsburgh, Pennsylvania 15260, United States.,Graduate School of Life and Environmental Sciences, Kyoto Prefectural University and ⊥Department of Biomolecular Engineering, Kyoto Institute of Technology , Kyoto 606, Japan
| | - Ryan L Slack
- Department of Structural Biology and ‡Department of Computational and Systems Biology, University of Pittsburgh School of Medicine , Pittsburgh, Pennsylvania 15260, United States.,Graduate School of Life and Environmental Sciences, Kyoto Prefectural University and ⊥Department of Biomolecular Engineering, Kyoto Institute of Technology , Kyoto 606, Japan
| | - Masayuki Oda
- Department of Structural Biology and ‡Department of Computational and Systems Biology, University of Pittsburgh School of Medicine , Pittsburgh, Pennsylvania 15260, United States.,Graduate School of Life and Environmental Sciences, Kyoto Prefectural University and ⊥Department of Biomolecular Engineering, Kyoto Institute of Technology , Kyoto 606, Japan
| | - Kenji Kanaori
- Department of Structural Biology and ‡Department of Computational and Systems Biology, University of Pittsburgh School of Medicine , Pittsburgh, Pennsylvania 15260, United States.,Graduate School of Life and Environmental Sciences, Kyoto Prefectural University and ⊥Department of Biomolecular Engineering, Kyoto Institute of Technology , Kyoto 606, Japan
| | - Daniel M Zuckerman
- Department of Structural Biology and ‡Department of Computational and Systems Biology, University of Pittsburgh School of Medicine , Pittsburgh, Pennsylvania 15260, United States.,Graduate School of Life and Environmental Sciences, Kyoto Prefectural University and ⊥Department of Biomolecular Engineering, Kyoto Institute of Technology , Kyoto 606, Japan
| | - Rieko Ishima
- Department of Structural Biology and ‡Department of Computational and Systems Biology, University of Pittsburgh School of Medicine , Pittsburgh, Pennsylvania 15260, United States.,Graduate School of Life and Environmental Sciences, Kyoto Prefectural University and ⊥Department of Biomolecular Engineering, Kyoto Institute of Technology , Kyoto 606, Japan
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11
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Johnson RA, Manley OM, Spuches AM, Grossoehme NE. Dissecting ITC data of metal ions binding to ligands and proteins. Biochim Biophys Acta Gen Subj 2015; 1860:892-901. [PMID: 26327285 DOI: 10.1016/j.bbagen.2015.08.018] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Revised: 08/19/2015] [Accepted: 08/25/2015] [Indexed: 01/12/2023]
Abstract
BACKGROUND ITC is a powerful technique that can reliably assess the thermodynamic underpinnings of a wide range of binding events. When metal ions are involved, complications arise in evaluating the data due to unavoidable solution chemistry that includes metal speciation and a variety of linked equilibria. SCOPE OF REVIEW This paper identifies these concerns, provides recommendations to avoid common mistakes, and guides the reader through the mathematical treatment of ITC data to arrive at a set of thermodynamic state functions that describe identical chemical events and, ideally, are independent of solution conditions. Further, common metal chromophores used in biological metal sensing studies are proposed as a robust system to determine unknown solution competition. MAJOR CONCLUSIONS Metal ions present several complications in ITC experiments. This review presents strategies to avoid these pitfalls and proposes and experimentally validates mathematical approaches to deconvolute complex equilibria that exist in these systems. GENERAL SIGNIFICANCE This review discusses the wide range of complications that exists in metal-based ITC experiments. It provides a starting point for scientists new to this field and articulates concerns that will help experienced researchers troubleshoot experiments.
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Affiliation(s)
- Rachel A Johnson
- Department of Chemistry, East Carolina University, Greenville, NC 27858, United States
| | - Olivia M Manley
- Department of Chemistry, Physics and Geology, Winthrop University, Rock Hill, SC 29730, United States
| | - Anne M Spuches
- Department of Chemistry, East Carolina University, Greenville, NC 27858, United States.
| | - Nicholas E Grossoehme
- Department of Chemistry, Physics and Geology, Winthrop University, Rock Hill, SC 29730, United States.
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12
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Achuthan V, Keith BJ, Connolly BA, DeStefano JJ. Human immunodeficiency virus reverse transcriptase displays dramatically higher fidelity under physiological magnesium conditions in vitro. J Virol 2014; 88:8514-27. [PMID: 24850729 PMCID: PMC4135932 DOI: 10.1128/jvi.00752-14] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2014] [Accepted: 05/15/2014] [Indexed: 12/24/2022] Open
Abstract
UNLABELLED The fidelity of human immunodeficiency virus (HIV) reverse transcriptase (RT) has been a subject of intensive investigation. The mutation frequencies for the purified enzyme in vitro vary widely but are typically in the 10(-4) range (per nucleotide addition), making the enzyme severalfold less accurate than most polymerases, including other RTs. This has often been cited as a factor in HIV's accelerated generation of genetic diversity. However, cellular experiments suggest that HIV does not have significantly lower fidelity than other retroviruses and shows a mutation frequency in the 10(-5) range. In this report, we reconcile, at least in part, these discrepancies by showing that HIV RT fidelity in vitro is in the same range as cellular results from experiments conducted with physiological (for lymphocytes) concentrations of free Mg(2+) (~0.25 mM) and is comparable to Moloney murine leukemia virus (MuLV) RT fidelity. The physiological conditions produced mutation rates that were 5 to 10 times lower than those obtained under typically employed in vitro conditions optimized for RT activity (5 to 10 mM Mg(2+)). These results were consistent in both commonly used lacZα complementation and steady-state fidelity assays. Interestingly, although HIV RT showed severalfold-lower fidelity under high-Mg(2+) (6 mM) conditions, MuLV RT fidelity was insensitive to Mg(2+). Overall, the results indicate that the fidelity of HIV replication in cells is compatible with findings of experiments carried out in vitro with purified HIV RT, providing more physiological conditions are used. IMPORTANCE Human immunodeficiency virus rapidly evolves through the generation and subsequent selection of mutants that can circumvent the immune response and escape drug therapy. This process is fueled, in part, by the presumably highly error-prone HIV polymerase reverse transcriptase (RT). Paradoxically, results of studies examining HIV replication in cells indicate an error frequency that is ~10 times lower than the rate for RT in the test tube, which invokes the possibility of factors that make RT more accurate in cells. This study brings the cellular and test tube results in closer agreement by showing that HIV RT is not more error prone than other RTs and, when assayed under physiological magnesium conditions, has a much lower error rate than in typical assays conducted using conditions optimized for enzyme activity.
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Affiliation(s)
- Vasudevan Achuthan
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland, USA
| | - Brian J Keith
- Institute of Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Bernard A Connolly
- Institute of Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Jeffrey J DeStefano
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland, USA
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Sponder G, Svidová S, Khan MB, Kolisek M, Schweyen RJ, Carugo O, Djinović-Carugo K. The G-M-N motif determines ion selectivity in the yeast magnesium channel Mrs2p. Metallomics 2013; 5:745-52. [PMID: 23686104 DOI: 10.1039/c3mt20201a] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The highly conserved G-M-N motif of the CorA-Mrs2-Alr1 family of Mg(2+) channels has been shown to be essential for Mg(2+) transport. We performed random mutagenesis of the G-M-N sequence of Saccharomyces cerevisiae Mrs2p in an unbiased genetic screen. A large number of mutants still capable of Mg(2+) influx, albeit below the wild-type level, were generated. Growth complementation assays, performed in media supplemented with Ca(2+) or Co(2+) or Mn(2+) or Zn(2+) at varying concentrations, lead to identification of mutants with reduced growth in the presence of Mn(2+) and Zn(2+). We hereby conclude that (1) at least two, but predominantly all three amino acids of the G-M-N motif must be replaced by certain combinations of other amino acids to remain functional, (2) replacement of any single amino acid within the G-M-N motif always impairs the function of Mrs2p, and (3) we show that the G-M-N motif determines ion selectivity, likely in concurrence with the negatively charged loop at the entrance of the channel thereby forming the Mrs2p selectivity filter.
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Affiliation(s)
- Gerhard Sponder
- Department of Microbiology, Immunobiology, Genetics, Max F. Perutz Laboratories, University of Vienna, Vienna, Austria
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14
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Khan MB, Sponder G, Sjöblom B, Svidová S, Schweyen RJ, Carugo O, Djinović-Carugo K. Structural and functional characterization of the N-terminal domain of the yeast Mg2+channel Mrs2. ACTA CRYSTALLOGRAPHICA SECTION D: BIOLOGICAL CRYSTALLOGRAPHY 2013; 69:1653-64. [DOI: 10.1107/s0907444913011712] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2013] [Accepted: 04/29/2013] [Indexed: 01/08/2023]
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15
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Viral enzymes containing magnesium: Metal binding as a successful strategy in drug design. Coord Chem Rev 2012. [DOI: 10.1016/j.ccr.2012.07.006] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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16
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Le Grice SFJ. Human immunodeficiency virus reverse transcriptase: 25 years of research, drug discovery, and promise. J Biol Chem 2012; 287:40850-7. [PMID: 23043108 DOI: 10.1074/jbc.r112.389056] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Synthesis of integration-competent, double-stranded DNA from the (+)-RNA strand genome of retroviruses and long terminal repeat-containing retrotransposons reflects a multistep process catalyzed by the virus-encoded reverse transcriptase (RT). In conjunction with RNA- and DNA-templated DNA synthesis, a hydrolytic activity of the same enzyme (RNase H) is required to remove genomic RNA of the RNA/DNA replication intermediate. Together, these combined synthetic and degradative functions ensure correct selection, extension, and removal of the RNA primers of (-)- and (+)-strand DNA synthesis (tRNA and the polypurine tract, respectively). For HIV-1 RT, a quarter century of research has not only illuminated the biochemical properties, structure, and conformational dynamics of this highly versatile enzyme but has also witnessed drug discovery advances from the first Food and Drug Administration-approved anti-RT drug to recent use of RT inhibitors as potential colorectal microbicides. Salient features of HIV-1 RT and extension of these findings into programs of drug discovery are reviewed here.
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Affiliation(s)
- Stuart F J Le Grice
- RT Biochemistry Section, HIV Drug Resistance Program, Frederick National Laboratory for Cancer Research, Frederick, Maryland 21702, USA.
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17
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Yanagita H, Fudo S, Urano E, Ichikawa R, Ogata M, Yokota M, Murakami T, Wu H, Chiba J, Komano J, Hoshino T. Structural Modulation Study of Inhibitory Compounds for Ribonuclease H Activity of Human Immunodeficiency Virus Type 1 Reverse Transcriptase. Chem Pharm Bull (Tokyo) 2012; 60:764-71. [DOI: 10.1248/cpb.60.764] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
| | - Satoshi Fudo
- Graduate School of Pharmaceutical Sciences, Chiba University
| | - Emiko Urano
- AIDS Research Center, National Institute of Infectious Diseases
| | - Reiko Ichikawa
- AIDS Research Center, National Institute of Infectious Diseases
| | - Masakazu Ogata
- Graduate School of Pharmaceutical Sciences, Chiba University
| | - Mizuho Yokota
- Graduate School of Pharmaceutical Sciences, Chiba University
| | | | - Honggui Wu
- AIDS Research Center, National Institute of Infectious Diseases
- Faculty of Industrial Science and Technology, Tokyo University of Science
| | - Joe Chiba
- Faculty of Industrial Science and Technology, Tokyo University of Science
| | - Jun Komano
- AIDS Research Center, National Institute of Infectious Diseases
| | - Tyuji Hoshino
- Graduate School of Pharmaceutical Sciences, Chiba University
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18
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Expression of an Mg2+-dependent HIV-1 RNase H construct for drug screening. Antimicrob Agents Chemother 2011; 55:4735-41. [PMID: 21768506 DOI: 10.1128/aac.00658-11] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A single polypeptide of the HIV-1 reverse transcriptase that reconstituted Mg(2+)-dependent RNase H activity has been made. Using molecular modeling, the construct was designed to encode the p51 subunit joined by a linker to the thumb (T), connection (C), and RNase H (R) domains of p66. This p51-G-TCR construct was purified from the soluble fraction of an Escherichia coli strain, MIC2067(DE3), lacking endogenous RNase HI and HII. The p51-G-TCR RNase H construct displayed Mg(2+)-dependent activity using a fluorescent nonspecific assay and showed the same cleavage pattern as HIV-1 reverse transcriptase (RT) on substrates that mimic the tRNA removal required for second-strand transfer reactions. The mutant E706Q (E478Q in RT) was purified under similar conditions and was not active. The RNase H of the p51-G-TCR RNase H construct and wild type HIV-1 RT had similar K(m)s for an RNA-DNA hybrid substrate and showed similar inhibition kinetics to two known inhibitors of the HIV-1 RT RNase H.
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19
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Structural and binding analysis of pyrimidinol carboxylic acid and N-hydroxy quinazolinedione HIV-1 RNase H inhibitors. Antimicrob Agents Chemother 2011; 55:2905-15. [PMID: 21464257 PMCID: PMC3101433 DOI: 10.1128/aac.01594-10] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
HIV-1 RNase H breaks down the intermediate RNA-DNA hybrids during reverse transcription, requiring two divalent metal ions for activity. Pyrimidinol carboxylic acid and N-hydroxy quinazolinedione inhibitors were designed to coordinate the two metal ions in the active site of RNase H. High-resolution (1.4 Å to 2.1 Å) crystal structures were determined with the isolated RNase H domain and reverse transcriptase (RT), which permit accurate assessment of the metal and water environment at the active site. The geometry of the metal coordination suggests that the inhibitors mimic a substrate state prior to phosphodiester catalysis. Surface plasmon resonance studies confirm metal-dependent binding to RNase H and demonstrate that the inhibitors do not bind at the polymerase active site of RT. Additional evaluation of the RNase H site reveals an open protein surface with few additional interactions to optimize active-site inhibitors.
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20
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Yan J, Wu H, Tom T, Brodsky O, Maegley K. Targeting Divalent Metal Ions at the Active Site of the HIV-1 RNase H Domain: NMR Studies on the Interactions of Divalent Metal Ions with RNase H and Its Inhibitors. ACTA ACUST UNITED AC 2011. [DOI: 10.4236/ajac.2011.26073] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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21
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Moomaw AS, Maguire ME. Cation selectivity by the CorA Mg2+ channel requires a fully hydrated cation. Biochemistry 2010; 49:5998-6008. [PMID: 20568735 PMCID: PMC2912426 DOI: 10.1021/bi1005656] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The CorA Mg(2+) channel is the primary uptake system in about half of all bacteria and archaea. However, the basis for its Mg(2+) selectivity is unknown. Previous data suggested that CorA binds a fully hydrated Mg(2+) ion, unlike other ion channels. The crystal structure of Thermotoga maritima CorA shows a homopentamer with two transmembrane segments per monomer connected by a short periplasmic loop. This highly conserved loop, (281)EFMPELKWS(289) in Salmonella enterica serovar Typhimurium CorA, is the only portion of the channel outside of the cell, suggesting a role in cation selectivity. Mutation of charged residues in the loop, E281 and K287, to any of several amino acids had little effect, demonstrating that despite conservation electrostatic interactions with these residues are not essential. While mutation of the universally conserved E285 gave a minimally functional channel, E285A and E285K mutants were the most functional, again indicating that the negative charge at this position is not a determining factor. Several mutations at K287 and W288 behaved anomalously in a transport assay. Analysis indicated that mutation of K287 and W288 disrupts cooperative interactions between distinct Mg(2+) binding sites. Overall, these results are not compatible with electrostatic interaction of the Mg(2+) ion with the periplasmic loop. Instead, the loop appears to form an initial binding site for hydrated Mg(2+), not for the dehydrated cation. The loop residues may function to accelerate dehydration of the before entry of Mg(2+) into the pore of the channel.
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Affiliation(s)
- Andrea S Moomaw
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965, USA.
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22
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Kirschberg TA, Balakrishnan M, Squires NH, Barnes T, Brendza KM, Chen X, Eisenberg EJ, Jin W, Kutty N, Leavitt S, Liclican A, Liu Q, Liu X, Mak J, Perry JK, Wang M, Watkins WJ, Lansdon EB. RNase H active site inhibitors of human immunodeficiency virus type 1 reverse transcriptase: design, biochemical activity, and structural information. J Med Chem 2009; 52:5781-4. [PMID: 19791799 DOI: 10.1021/jm900597q] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Pyrimidinol carboxylic acids were designed as inhibitors of HIV-1 RNase H function. These molecules can coordinate to two divalent metal ions in the RNase H active site. Inhibition of enzymatic activity was measured in a biochemical assay, but no antiviral effect was observed. Binding was demonstrated via a solid state structure of the isolated p15-Ec domain of HIV-1 RT showing inhibitor and two Mn(II) ions bound to the RNase H active site.
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Affiliation(s)
- Thorsten A Kirschberg
- Department of Medicinal Chemistry, Gilead Sciences, Foster City, California 94404, USA.
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23
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Wendeler M, Beilhartz GL, Beutler JA, Götte M, Le Grice SFJ. HIV ribonuclease H: continuing the search for small molecule antagonists. HIV THERAPY 2008; 3:39-53. [PMID: 38961883 PMCID: PMC11221599 DOI: 10.2217/17584310.3.1.39] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/05/2024]
Abstract
Members of the ribonuclease H (RNase H) family of enzymes (EC 3.1.26.4), which are found in nearly all organisms, are endoribonucleases that specifically hydrolyze the phosphodiester bond of RNA in a RNA-DNA hybrid. In retroviruses such as HIV-1, the RNase H activity is part of reverse transcriptase, the enzyme that converts the viral ssRNA into dsDNA suitable for integration into the host cell genome. In HIV-1, RNase H plays an essential role in various stages of reverse transcription, and it has been known for 20 years that inhibiting RNase H activity renders HIV noninfectious. However, the development of potent and selective antagonists of HIV RNase H has made surprisingly slow progress, and so far no RNase H inhibitor is in clinical trial, rendering this enzyme an important, but as yet underexplored, drug target. The recently described crystal structure of human RNase H in complex with a RNA-DNA hybrid provides new insight into the mechanism of HIV RNase H activity, with the potential to unveil new niches for therapeutic intervention. The current status of RNase H screening efforts is reviewed here.
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Affiliation(s)
- Michaela Wendeler
- HIV Drug Resistance Program, National Cancer Institute-Frederick, Frederick, MD, USA
| | - Greg L Beilhartz
- Department of Microbiology & Immunology, McGill University, Montreal, QC, Canada
| | - John A Beutler
- Molecular Targets Discovery Program, National Cancer Institute-Frederick, Frederick, MD, USA
| | - Matthias Götte
- Department of Microbiology & Immunology, McGill University, Montreal, QC, Canada
| | - Stuart FJ Le Grice
- HIV Drug Resistance Program, National Cancer Institute-Frederick, Frederick, MD, USA
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24
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Sarafianos SG, Marchand B, Das K, Himmel DM, Parniak MA, Hughes SH, Arnold E. Structure and function of HIV-1 reverse transcriptase: molecular mechanisms of polymerization and inhibition. J Mol Biol 2008; 385:693-713. [PMID: 19022262 DOI: 10.1016/j.jmb.2008.10.071] [Citation(s) in RCA: 339] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2008] [Revised: 10/15/2008] [Accepted: 10/15/2008] [Indexed: 11/19/2022]
Abstract
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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Affiliation(s)
- Stefan G Sarafianos
- Christopher Bond Life Sciences Center, Department of Molecular Microbiology & Immunology, University of Missouri School of Medicine, Columbia, MO 65211, USA
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25
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Wilcox DE. Isothermal titration calorimetry of metal ions binding to proteins: An overview of recent studies. Inorganica Chim Acta 2008. [DOI: 10.1016/j.ica.2007.10.032] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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26
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Schultz SJ, Champoux JJ. RNase H activity: structure, specificity, and function in reverse transcription. Virus Res 2008; 134:86-103. [PMID: 18261820 DOI: 10.1016/j.virusres.2007.12.007] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2007] [Revised: 12/13/2007] [Accepted: 12/13/2007] [Indexed: 01/20/2023]
Abstract
This review compares the well-studied RNase H activities of human immunodeficiency virus, type 1 (HIV-1) and Moloney murine leukemia virus (MoMLV) reverse transcriptases. The RNase H domains of HIV-1 and MoMLV are structurally very similar, with functions assigned to conserved subregions like the RNase H primer grip and the connection subdomain, as well as to distinct features like the C-helix and loop in MoMLV RNase H. Like cellular RNases H, catalysis by the retroviral enzymes appears to involve a two-metal ion mechanism. Unlike cellular RNases H, the retroviral RNases H display three different modes of cleavage: internal, DNA 3' end-directed, and RNA 5' end-directed. All three modes of cleavage appear to have roles in reverse transcription. Nucleotide sequence is an important determinant of cleavage specificity with both enzymes exhibiting a preference for specific nucleotides at discrete positions flanking an internal cleavage site as well as during tRNA primer removal and plus-strand primer generation. RNA 5' end-directed and DNA 3' end-directed cleavages show similar sequence preferences at the positions closest to a cleavage site. A model for how RNase H selects cleavage sites is presented that incorporates both sequence preferences and the concept of a defined window for allowable cleavage from a recessed end. Finally, the RNase H activity of HIV-1 is considered as a target for anti-virals as well as a participant in drug resistance.
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Affiliation(s)
- Sharon J Schultz
- Department of Microbiology, School of Medicine, Box 357242, University of Washington, Seattle, WA 98195, USA
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27
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Yarrington RM, Chen J, Bolton EC, Boeke JD. Mn2+ suppressor mutations and biochemical communication between Ty1 reverse transcriptase and RNase H domains. J Virol 2007; 81:9004-12. [PMID: 17537863 PMCID: PMC1951463 DOI: 10.1128/jvi.02502-06] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ty1 reverse transcriptase/RNase H (RT/RH) is exquisitely sensitive to manganese concentrations. Elevated intracellular free Mn(2+) inhibits Ty1 retrotransposition and in vitro Ty1 RT-polymerizing activity. Furthermore, Mn(2+) inhibition is not limited to the Ty1 RT, as this ion similarly inhibits the activities of both avian myeloblastosis virus and human immunodeficiency virus type 1 RTs. To further characterize Mn(2+) inhibition, we generated RT/RH suppressor mutants capable of increased Ty1 transposition in pmr1 Delta cells. PMR1 codes for a P-type ATPase that regulates intracellular calcium and manganese ion homeostasis, and pmr1 mutants accumulate elevated intracellular manganese levels and display 100-fold less transposition than PMR1(+) cells. Mapping of these suppressor mutations revealed, surprisingly, that suppressor point mutations localize not to the RT itself but to the RH domain of the protein. Furthermore, Mn(2+) inhibition of in vitro RT activity is greatly reduced in all the suppressor mutants, whereas RH activity and cleavage specificity remain largely unchanged. These intriguing results reveal that the effect of these suppressor mutations is transmitted to the polymerase domain and suggest biochemical communication between these two domains during reverse transcription.
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Affiliation(s)
- Robert M Yarrington
- Department of Molecular Biology and Genetics, The Johns Hopkins University School of Medicine, 733 N. Broadway, Baltimore MD 21205, USA
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28
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Bohlayer WP, DeStefano JJ. Tighter binding of HIV reverse transcriptase to RNA-DNA versus DNA-DNA results mostly from interactions in the polymerase domain and requires just a small stretch of RNA-DNA. Biochemistry 2006; 45:7628-38. [PMID: 16768458 PMCID: PMC2519887 DOI: 10.1021/bi051770w] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Binding of HIV reverse transcriptase (RT) to unique substrates that positioned RNA-DNA or DNA-DNA near the polymerase or RNase H domains was measured. The substrates consisted of a 50 nucleotide template and DNA primers ranging from 23 to 43 nucleotides. Five different types of template strands were used: homogeneous (1) RNA or (2) DNA, (3) the first 20 5' nucleotides of DNA and the last 30 RNA, (4) the first 20 RNA and the last 30 DNA, and (5) 15 nucleotides of DNA followed by 5 RNA and then 30 DNA. The different length primers were designed to position RT over various regions of the template. Dissociation rate constants were determined for each of the substrates. Results showed that the severalfold tighter binding to RNA-DNA vs DNA-DNA was determined by binding in the polymerase domain and required only a short 5 base pair RNA-DNA hybrid region. Chimeric substrates with RNA-DNA positioned near the polymerase domain and DNA-DNA near the RNase H domain showed binding comparable to a complete RNA-DNA substrate, while those with the reverse orientation were comparable to DNA-DNA. Interestingly, the first configuration, though binding as tightly as RNA-DNA, could not be cleaved by RT RNase H activity, a finding that could perhaps be exploited in the development of nucleic acid-based inhibitors.
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Affiliation(s)
| | - Jeffrey J. DeStefano
- Corresponding author: Address: Department of Cell Biology and Molecular Genetics, University of Maryland, Building 231, College Park, MD 20742 (p) 301-405-5449; (f) 301-314-9489; (e)
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29
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Ercanli T, Boyd DB. Exploration of the conformational space of a polymeric material that inhibits human immunodeficiency virus. J Chem Inf Model 2006; 46:1321-33. [PMID: 16711751 DOI: 10.1021/ci050339a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Baertschi et al. (Antiviral Chem. Chemother. 1997, 8, 353-362) clarified the nature of a polymeric degradation product formed from the cephalosporin ceftazidime. Interest in the polymeric material arises from its ability to inhibit the RNase H and polymerase activities of HIV-1 reverse transcriptase (RT). To shed light on the structure of the polymeric material like that which forms from degradation of third-generation cephalosporins, we apply molecular modeling and other computational chemistry techniques. Aminothiazole methoxime (2-amino-4-thiazolyl-methoxyimino; ATMO) is the parent structure related to the isolated degradation product of ceftazidime. The MMFF94 force field and Monte Carlo multiple minimum method as implemented in MacroModel are used to generate low-energy conformers. We built up oligomeric models starting from the trimer to the 16-mer and performed distribution analyses on the dihedral angles from the Monte Carlo runs to analyze the three-dimensional shapes of the oligomers. Although the larger oligomers are too long for a complete search of conformational space, the low-energy conformers examined do not show secondary structure or repetitive conformations. Polymeric ATMO material may, therefore, exhibit only random coil conformations. Topological similarity of ATMO structures to other reported RT inhibitors is also examined.
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Affiliation(s)
- Tulay Ercanli
- Department of Chemistry and Chemical Biology, Indiana University-Purdue University at Indianapolis, 402 North Blackford Street, Indianapolis, Indiana 46202-3274, USA
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30
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Chon H, Matsumura H, Koga Y, Takano K, Kanaya S. Crystal structure and structure-based mutational analyses of RNase HIII from Bacillus stearothermophilus: a new type 2 RNase H with TBP-like substrate-binding domain at the N terminus. J Mol Biol 2005; 356:165-78. [PMID: 16343535 DOI: 10.1016/j.jmb.2005.11.017] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2005] [Revised: 11/02/2005] [Accepted: 11/06/2005] [Indexed: 10/25/2022]
Abstract
Ribonuclease HIII (Bst-RNase HIII) from the moderate thermophile Bacillus stearothermophilus is a type 2 RNase H but shows poor amino acid sequence identity with another type 2 RNase H, RNase HII. It is composed of 310 amino acid residues and acts as a monomer. Bst-RNase HIII has a large N-terminal extension with unknown function and a unique active-site motif (DEDE), both of which are characteristics common to RNases HIII. To understand the role of these N-terminal extension and active-site residues, the crystal structure of Bst-RNase HIII was determined in both metal-free and metal-bound forms at 2.1-2.6 angstroms resolutions. According to these structures, Bst-RNase HIII consists of the N-terminal domain and C-terminal RNase H domain. The structures of the N and C-terminal domains were similar to those of TATA-box binding proteins and archaeal RNases HII, respectively. The steric configurations of the four conserved active-site residues were very similar to those of other type 1 and type 2 RNases H. Single Mn and Mg ions were coordinated with Asp97, Glu98, and Asp202, which correspond to Asp10, Glu48, and Asp70 of Escherichia coli RNase HI, respectively. The mutational studies indicated that the replacement of either one of these residues with Ala resulted in a great reduction of the enzymatic activity. Overproduction, purification, and characterization of the Bst-RNase HIII derivatives with N and/or C-terminal truncations indicated that the N-terminal domain and C-terminal helix are involved in substrate binding, but the former contributes to substrate binding more greatly than the latter.
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Affiliation(s)
- Hyongi Chon
- Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
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Budihas SR, Gorshkova I, Gaidamakov S, Wamiru A, Bona MK, Parniak MA, Crouch RJ, McMahon JB, Beutler JA, Le Grice SFJ. Selective inhibition of HIV-1 reverse transcriptase-associated ribonuclease H activity by hydroxylated tropolones. Nucleic Acids Res 2005; 33:1249-56. [PMID: 15741178 PMCID: PMC552956 DOI: 10.1093/nar/gki268] [Citation(s) in RCA: 156] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
High-throughput screening of a National Cancer Institute library of pure natural products identified the hydroxylated tropolone derivatives beta-thujaplicinol (2,7-dihydroxy-4-1(methylethyl)-2,4,6-cycloheptatrien-1-one) and manicol (1,2,3,4-tetrahydro-5-7-dihydroxy-9-methyl-2-(1-methylethenyl)-6H-benzocyclohepten-6-one) as potent and selective inhibitors of the ribonuclease H (RNase H) activity of human immunodeficiency virus-type 1 reverse transcriptase (HIV-1 RT). beta-Thujaplicinol inhibited HIV-1 RNase H in vitro with an IC50 of 0.2 microM, while the IC50 for Escherichia coli and human RNases H was 50 microM and 5.7 microM, respectively. In contrast, the related tropolone analog beta-thujaplicin (2-hydroxy-4-(methylethyl)-2,4,6-cycloheptatrien-1-one), which lacks the 7-OH group of the heptatriene ring, was inactive, while manicol, which possesses a 7-OH group, inhibited HIV-1 and E.coli RNases H with IC50 = 1.5 microM and 40 microM, respectively. Such a result highlights the importance of the 2,7-dihydroxy function of these tropolone analogs, possibly through a role in metal chelation at the RNase H active site. Inhibition of HIV-2 RT-associated RNase H indirectly indicates that these compounds do not occupy the nonnucleoside inhibitor-binding pocket in the vicinity of the DNA polymerase domain. Both beta-thujaplicinol and manicol failed to inhibit DNA-dependent DNA polymerase activity of HIV-1 RT at a concentration of 50 microM, suggesting that they are specific for the C-terminal RNase H domain, while surface plasmon resonance studies indicated that the inhibition was not due to intercalation of the analog into the nucleic acid substrate. Finally, we have demonstrated synergy between beta-thujaplicinol and calanolide A, a nonnucleoside inhibitor of HIV-1 RT, raising the possibility that both enzymatic activities of HIV-1 RT can be simultaneously targeted.
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Affiliation(s)
| | - Inna Gorshkova
- Protein Biophysics Resource, Division of Bioengineering and Physical Sciences, National Institutes of HealthBethesda, MD 20892, USA
| | - Sergei Gaidamakov
- Laboratory of Molecular Genetics, National Institute of Child Health and Human DevelopmentBethesda, MD 20892, USA
| | - Antony Wamiru
- Molecular Targets Development Program, National Cancer Institute at FrederickFrederick, MD 21702, USA
- SAIC-Frederick, FrederickMD 21702, USA
| | | | - Michael A. Parniak
- Division of Infectious Diseases, School of Medicine, University of PittsburghPittsburgh, PA 15213, USA
| | - Robert J. Crouch
- Laboratory of Molecular Genetics, National Institute of Child Health and Human DevelopmentBethesda, MD 20892, USA
| | - James B. McMahon
- Molecular Targets Development Program, National Cancer Institute at FrederickFrederick, MD 21702, USA
| | - John A. Beutler
- Molecular Targets Development Program, National Cancer Institute at FrederickFrederick, MD 21702, USA
| | - Stuart F. J. Le Grice
- To whom correspondence should be addressed. Tel: +1 301 846 5256; Fax: +1 301 846 6013;
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32
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Tsunaka Y, Takano K, Matsumura H, Yamagata Y, Kanaya S. Identification of Single Mn2+ Binding Sites Required for Activation of the Mutant Proteins of E.coli RNase HI at Glu48 and/or Asp134 by X-ray Crystallography. J Mol Biol 2005; 345:1171-83. [PMID: 15644213 DOI: 10.1016/j.jmb.2004.11.007] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2004] [Revised: 11/03/2004] [Accepted: 11/04/2004] [Indexed: 10/26/2022]
Abstract
Escherichia coli RNase HI has two Mn(2+)-binding sites. Site 1 is formed by Asp10, Glu48, and Asp70, and site 2 is formed by Asp10 and Asp134. Site 1 and site 2 have been proposed to be an activation site and an attenuation site, respectively. However, Glu48 and Asp134 are dispensable for Mn(2+)-dependent activity. In order to identify the Mn(2+)-binding sites of the mutant proteins at Glu48 and/or Asp134, the crystal structures of the mutant proteins E48A-RNase HI*, D134A-RNase HI*, and E48A/D134N-RNase HI* in complex with Mn(2+) were determined. In E48A-RNase HI*, Glu48 and Lys87 are replaced by Ala. In D134A-RNase HI*, Asp134 and Lys87 are replaced by Ala. In E48A/D134N-RNase HI*, Glu48 and Lys87 are replaced by Ala and Asp134 is replaced by Asn. All crystals had two or four protein molecules per asymmetric unit and at least two of which had detectable manganese ions. These structures indicated that only one manganese ion binds to the various positions around the center of the active-site pocket. These positions are different from one another, but none of them is similar to site 1. The temperature factors of these manganese ions were considerably larger than those of the surrounding residues. These results suggest that the first manganese ion required for activation of the wild-type protein fluctuates among various positions around the center of the active-site pockets. We propose that this fluctuation is responsible for efficient hydrolysis of the substrates by the protein (metal fluctuation model). The binding position of the first manganese ion is probably forced to shift to site 1 or site 2 upon binding of the second manganese ion.
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Affiliation(s)
- Yasuo Tsunaka
- Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
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33
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Bibillo A, Lener D, Klarmann GJ, Le Grice SFJ. Functional roles of carboxylate residues comprising the DNA polymerase active site triad of Ty3 reverse transcriptase. Nucleic Acids Res 2005; 33:171-81. [PMID: 15647500 PMCID: PMC546138 DOI: 10.1093/nar/gki150] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Aspartic acid residues comprising the -D-(aa)n-Y-L-D-D- DNA polymerase active site triad of reverse transcriptase from the Saccharomyces cerevisiae long terminal repeat-retrotransposon Ty3 (Asp151, Asp213 and Asp214) were evaluated via site-directed mutagenesis. An Asp151→Glu substitution showed a dramatic decrease in catalytic efficiency and a severe translocation defect following initiation of DNA synthesis. In contrast, enzymes harboring the equivalent alteration at Asp213 and Asp214 retained DNA polymerase activity. Asp151→Asn and Asp213→Asn substitutions eliminated both polymerase activities. However, while Asp214 of the triad could be replaced by either Asn or Glu, introducing Gln seriously affected processivity. Mutants of the carboxylate triad at positions 151 and 213 also failed to catalyze pyrophosphorolysis. Finally, alterations to the DNA polymerase active site affected RNase H activity, suggesting a close spatial relationship between these N- and C-terminal catalytic centers. Taken together, our data reveal a critical role for Asp151 and Asp213 in catalysis. In contrast, the second carboxylate of the Y-L-D-D motif (Asp214) is not essential for catalysis, and possibly fulfills a structural role. Although Asp214 was most insensitive to substitution with respect to activity of the recombinant enzyme, all alterations at this position were lethal for Ty3 transposition.
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Affiliation(s)
| | | | | | - Stuart F. J. Le Grice
- To whom correspondence should be addressed. Tel: +1 301 846 5256; Fax: +1 301 846 6013;
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34
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Klumpp K, Hang JQ, Rajendran S, Yang Y, Derosier A, Wong Kai In P, Overton H, Parkes KEB, Cammack N, Martin JA. Two-metal ion mechanism of RNA cleavage by HIV RNase H and mechanism-based design of selective HIV RNase H inhibitors. Nucleic Acids Res 2004; 31:6852-9. [PMID: 14627818 PMCID: PMC290251 DOI: 10.1093/nar/gkg881] [Citation(s) in RCA: 127] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Human immunodeficiency virus (HIV) RNase H activity is essential for the synthesis of viral DNA by HIV reverse transcriptase (HIV-RT). RNA cleavage by RNase H requires the presence of divalent metal ions, but the role of metal ions in the mechanism of RNA cleavage has not been resolved. We measured HIV RNase H activity associated with HIV-RT protein in the presence of different concentrations of either Mg2+, Mn2+, Co2+ or a combination of these divalent metal ions. Polymerase-independent HIV RNase H was similar to or more active with Mn2+ and Co2+ compared with Mg2+. Activation of RNase H by these metal ions followed sigmoidal dose-response curves suggesting cooperative metal ion binding. Titration of Mg2+-bound HIV RNase H with Mn2+ or Co2+ ions generated bell-shaped activity dose-response curves. Higher activity could be achieved through simultaneous binding of more than one divalent metal ion at intermediate Mn2+ and Co2+ concentrations, and complete replacement of Mg2+ occurred at higher Mn2+ or Co2+ concentrations. These results are consistent with a two-metal ion mechanism of RNA cleavage as previously suggested for a number of polymerase-associated nucleases. In contrast, the structurally highly homologous RNase HI from Escherichia coli is most strongly activated by Mg2+, is significantly inhibited by submillimolar concentrations of Mn2+ and most probably cleaves RNA via a one-metal ion mechanism. Based on this difference in active site structure, a series of small molecule N-hydroxyimides was identified with significant enzyme inhibitory potency and selectivity for HIV RNase H.
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35
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Tsunaka Y, Haruki M, Morikawa M, Oobatake M, Kanaya S. Dispensability of glutamic acid 48 and aspartic acid 134 for Mn2+-dependent activity of Escherichia coli ribonuclease HI. Biochemistry 2003; 42:3366-74. [PMID: 12641469 DOI: 10.1021/bi0205606] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The activities of the eight mutant proteins of Escherichia coli RNase HI, in which the four carboxylic amino acids (Asp(10), Glu(48), Asp(70), and Asp(134)) involved in catalysis are changed to Asn (Gln) or Ala, were examined in the presence of Mn(2+). Of these proteins, the E48A, E48Q, D134A, and D134N proteins exhibited the activity, indicating that Glu(48) and Asp(134) are dispensable for Mn(2+)-dependent activity. The maximal activities of the E48A and D134A proteins were comparable to that of the wild-type protein. However, unlike the wild-type protein, these mutant proteins exhibited the maximal activities in the presence of >100 microM MnCl(2), and their activities were not inhibited at higher Mn(2+) concentrations (up to 10 mM). The wild-type protein contains two Mn(2+) binding sites and is activated upon binding of one Mn(2+) ion at site 1 at low ( approximately 1 microM) Mn(2+) concentrations. This activity is attenuated upon binding of a second Mn(2+) ion at site 2 at high (>10 microM) Mn(2+) concentrations. The cleavage specificities of the mutant proteins, which were examined using oligomeric substrates at high Mn(2+) concentrations, were identical to that of the wild-type protein at low Mn(2+) concentrations but were different from that of the wild-type protein at high Mn(2+) concentrations. These results suggest that one Mn(2+) ion binds to the E48A, E48Q, D134A, and D134N proteins at site 1 or a nearby site with weaker affinities. The binding analyses of the Mn(2+) ion to these proteins in the absence of the substrate support this hypothesis. When Mn(2+) ion is used as a metal cofactor, the Mn(2+) ion itself, instead of Glu(48) and Asp(134), probably holds water molecules required for activity.
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Affiliation(s)
- Yasuo Tsunaka
- Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
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36
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Lai B, Li Y, Cao A, Lai L. Metal ion binding and enzymatic mechanism of Methanococcus jannaschii RNase HII. Biochemistry 2003; 42:785-91. [PMID: 12534291 DOI: 10.1021/bi026960a] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
RNase H degrades the RNA moiety in DNA:RNA hybrid in a divalent metal ion dependent manner. It is essential to understand the role of metal ion in enzymatic mechanism. One of the key points in this study is how many metal ions are involved in the enzyme catalysis. Accordingly, either one-metal binding mechanism or two-metal binding mechanism is proposed. We have studied the thermodynamic properties of four metal ions (Mg(2+), Mn(2+), Ca(2+), and Ba(2+)) binding to Methanococcus jannaschii RNase HII using isothermal titration calorimetry. All of the four metal ions were found to bind Mj RNase HII with 1:1 stoichiometry in the absence of substrate. Together with enzymatic activity assay data, we propose that only one metal ion binding to the enzyme in catalytic process. We also studied the pH dependence of metal binding and enzyme activity and found that at pH 6.5, Mg(2+) did not bind to the enzyme without the substrate but still activated the enzyme to about 2% of its maximum activity (in 10 mM Mn(2+) at pH 8). This implies that the substrate may also be incorporated in metal ion binding and help to position the metal ion. To find which acidic residues correspond to metal ion binding, we also studied the binding thermodynamics and enzymatic activity assay of four mutants: D7N, E8Q, D112N, and D149N in the presence of Mn(2+). The thermodynamic parameters are least affected for the D149N mutant, which has a very low enzymatic activity. This indicates that Asp149 is essential for the enzymatic activity. On the basis of all these observations, we suggest a metal binding model in which D7, E8, and D112 bind the metal ion and D149 activates a water molecule to attack the P-O bond in the RNA chain of the substrate.
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Affiliation(s)
- Bing Lai
- State Key Laboratory for Structural Chemistry Studies of Stable and Unstable Species, Institute of Physical Chemistry, College of Chemistry, Peking University, Beijing 100871, China
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37
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Pari K, Mueller GA, DeRose EF, Kirby TW, London RE. Solution structure of the RNase H domain of the HIV-1 reverse transcriptase in the presence of magnesium. Biochemistry 2003; 42:639-50. [PMID: 12534276 DOI: 10.1021/bi0204894] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This paper presents the first solution structure of the RNase H domain of HIV-1 reverse transcriptase (RT) determined by NMR methods. The solution conditions in this study were at physiological pH in the presence of Mg(2+). An investigation of the dependence of the (1)H-(15)N HSQC spectrum of the RNase H domain on [Mg(2+)] indicates that Mg(2+) produces significant, global effects on the amide chemical shifts, implying that divalent metal ion binding is important for stabilizing the structure of the isolated domain in solution. Analysis of amide shift data as a function of MgCl(2) concentration using either a single- or two-site binding model indicated that the latter provided a significantly improved fit, with the K(D) for site A = 2.7-3.2 mM and K(D) for site B approximately 35 mM, calculated on the assumption that site A is already occupied. Resonances of the [U-(13)C,(15)N]RNase H domain, measured at pH 6.8, in 80 mM MgCl(2), were assigned and NOESY data collected in order to determine the structure. Assignment of the NOESY spectra using the ARIA program resulted in a high-resolution structure for residues 6-114 which was similar to the crystal structure of the isolated domain,. The data were insufficient to define a compact structure for the C-terminal residues after 114. Residues I134-L138 located at the C-terminus are highly disordered and give rise to relatively sharp and intense amide resonances, while the amide resonances for the segment from E124 to A132 appear to be largely absent and are presumably subject to significant exchange broadening between different conformational states. Comparisons with crystal structure data for the full reverse transcriptase molecule indicate that the corresponding region is absent in nearly all of the crystal structures determined for the P2(1)2(1)2(1) space group, while these residues adopt an alpha-helix in structures determined for other symmetry groups. This structural heterogeneity indicates that significant conformational variability exists for this segment of the full reverse transcriptase enzyme as well, and the structure of the C-terminal peptide can be selected or deselected, depending on crystallization conditions. This analysis, along with the structural characterization contained herein, challenges the previous paradigm that the dynamic behavior of the isolated RNase H domain differs substantially from the behavior in the intact enzyme. The poor Mg(2+) binding and conformational flexibility of residues located near the active site indicate that substrate binding is a precondition for metal ion binding and for selecting the active site conformation of the RNase H domain.
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Affiliation(s)
- Koteppa Pari
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health, P.O. Box 12233, Research Triangle Park, North Carolina 27709, USA
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38
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Cristofaro JV, Rausch JW, Le Grice SFJ, DeStefano JJ. Mutations in the ribonuclease H active site of HIV-RT reveal a role for this site in stabilizing enzyme-primer-template binding. Biochemistry 2002; 41:10968-75. [PMID: 12206668 DOI: 10.1021/bi025871v] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The RNase H activity of HIV-RT is coordinated by a catalytic triad (E478, D443, D498) of acidic residues that bind divalent cations. We examined the effect of RNase H deficient E(478)-->Q and D(549)-->N mutations that do not alter polymerase activity on binding of enzyme to various nucleic acid substrates. Binding of the mutant and wild-type enzymes to various nucleic acid substrates was examined by determining dissociation rate constants (k(off)) by titrating both Mg(2+) and salt concentrations. In agreement with the unaltered polymerase activity of the mutant, the k(off) values for the wild-type and mutant enzymes were essentially identical using DNA-DNA templates in the presence of 6 mM Mg(2+). However, with lower concentrations of Mg(2+) and in the absence of Mg(2+), although both enzymes dissociated more rapidly, the mutant enzymes dissociated several-fold more slowly than the wild type. This was also observed on RNA-DNA templates. These results indicate that alterations in residues essential for Mg(2+) binding have a pronounced positive effect on enzyme-template stability and that the negative residues in the RNase H region of the enzyme have a negative influence on binding in the absence of Mg(2+). In this regard RT is similar to other nucleic acid cleaving enzymes that show enhanced binding upon mutation of active site residues.
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Affiliation(s)
- Jason V Cristofaro
- Department of Cell Biology and Molecular Genetics, University of Maryland College Park, Building 231, College Park, Maryland 20742, USA
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39
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Hadden JM, Déclais AC, Phillips SE, Lilley DM. Metal ions bound at the active site of the junction-resolving enzyme T7 endonuclease I. EMBO J 2002; 21:3505-15. [PMID: 12093751 PMCID: PMC126086 DOI: 10.1093/emboj/cdf337] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
T7 endonuclease I is a nuclease that is selective for the structure of the four-way DNA junction. The active site is similar to those of a number of restriction enzymes. We have solved the crystal structure of endonuclease I with a wild-type active site. Diffusion of manganese ions into the crystal revealed two peaks of electron density per active site, defining two metal ion-binding sites. Site 1 is fully occupied, and the manganese ion is coordinated by the carboxylate groups of Asp55 and Glu65, and the main chain carbonyl of Thr66. Site 2 is partially occupied, and the metal ion has a single protein ligand, the remaining carboxylate oxygen atom of Asp55. Isothermal titration calorimetry showed the sequential exothermic binding of two manganese ions in solution, with dissociation constants of 0.58 +/- 0.019 and 14 +/- 1.5 mM. These results are consistent with a two metal ion mechanism for the cleavage reaction, in which the hydrolytic water molecule is contained in the first coordination sphere of the site 1-bound metal ion.
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Affiliation(s)
| | - Anne-Cécile Déclais
- Astbury Centre for Structural Molecular Biology, School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT and
Cancer Research UK Nucleic Acid Structure Research Group, Department of Biochemistry, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, UK Corresponding author e-mail:
| | | | - David M.J. Lilley
- Astbury Centre for Structural Molecular Biology, School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT and
Cancer Research UK Nucleic Acid Structure Research Group, Department of Biochemistry, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, UK Corresponding author e-mail:
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40
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DeStefano JJ, Cristofaro JV, Derebail S, Bohlayer WP, Fitzgerald-Heath MJ. Physical mapping of HIV reverse transcriptase to the 5' end of RNA primers. J Biol Chem 2001; 276:32515-21. [PMID: 11441011 DOI: 10.1074/jbc.m103958200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Enzymatic analysis of RNA cleavage products has suggested that human immunodeficiency virus (HIV) reverse transcriptase (RT) binds to the 5' end of RNAs that are recessed on a longer DNA template (RNA primers) yet binds to the 3' end of DNA primers. One concern is that RT molecules bound at the 3' end of RNA would not be easily detected because RT may not catalyze substantial RNA extension or cleavage when bound to the 3' end. We used physical mapping to show that RT binds preferentially to the 5' end of RNA primers. An HIV-RT that lacked RNase H activity (HIV-RT(E478Q)) was incubated with the RNA-DNA hybrid followed by the addition of Escherichia coli RNase H. RT protected a approximately 23-base region at the 5' end of the RNA and 4 additional bases on the DNA strand. This footprint correlated well with the crystal structure of HIV-RT. No protection of the RNA 3' end was observed, although when dNTPs were included, low levels of extension occurred, indicating that RT can bind this end. Wild-type HIV-RT cleaved the RNA and then extended a small portion of the cleaved fragments, suggesting that very small RNAs may be bound similar to DNA primers.
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Affiliation(s)
- J J DeStefano
- Department of Cell Biology and Molecular Genetics, University of Maryland College Park, College Park, Maryland 20742, USA
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41
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Goedken ER, Marqusee S. Co-crystal of Escherichia coli RNase HI with Mn2+ ions reveals two divalent metals bound in the active site. J Biol Chem 2001; 276:7266-71. [PMID: 11083878 DOI: 10.1074/jbc.m009626200] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ribonuclease H (RNase H) selectively degrades the RNA strand of RNA.DNA hybrids in a divalent cation-dependent manner. Previous structural studies revealed a single Mg(2+) ion-binding site in Escherichia coli RNase HI. In the crystal structure of the related RNase H domain of human immunodeficiency virus reverse transcriptase, however, two Mn(2+) ions were observed suggesting a different mode of metal binding. E. coli RNase HI shows catalytic activity in the presence of Mg(2+) or Mn(2+) ions, but these two metals show strikingly different optimal concentrations. Mg(2+) ions are required in millimolar concentrations, but Mn(2+) ions are only required in micromolar quantities. Based upon the metal dependence of E. coli RNase HI activity, we proposed an activation/attenuation model in which one metal is required for catalysis, and binding of a second metal is inhibitory. We have now solved the co-crystal structure of E. coli RNase HI with Mn(2+) ions at 1.9-A resolution. Two octahedrally coordinated Mn(2+) ions are seen to bind to the enzyme-active site. Residues Asp-10, Glu-48, and Asp-70 make direct (inner sphere) coordination contacts to the first (activating) metal, whereas residues Asp-10 and Asp-134 make direct contacts to the second (attenuating) metal. This structure is consistent with biochemical evidence suggesting that two metal ions may bind RNase H but liganding a second ion inhibits RNase H activity.
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Affiliation(s)
- E R Goedken
- Department of Molecular and Cell Biology, University of California, Berkeley 94720, USA
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