1
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Johnson KA. You get what you screen for: Standards for experimental design and data fitting in drug discovery. Methods Enzymol 2023; 690:131-157. [PMID: 37858528 DOI: 10.1016/bs.mie.2023.08.003] [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] [Indexed: 10/21/2023]
Abstract
A common mantra in drug discovery is that "You get what you screen for." This is not a promise that you will always get an effective drug candidate, but rather a warning that inaccuracies in your protocol for screening will more likely produce a compound that fails to be an effective candidate because it matches the properties of your screen, not the desired features of an ideal lead compound. It is with this in mind that we examine the current protocols for evaluating drug candidates and highlight some deficiencies while pointing the way to better methods. Many of the errors in data fitting can be rectified by abandoning the traditional equation-based data fitting methods and adopting the more rigorous mechanism-based fitting afforded by computer simulation based on numerical integration of rate equations. Using these methods bypasses the errors in judgement in choosing the appropriate equation for data fitting and the approximations required to derive those equations. In this chapter we outline the limitations and systematic errors in conventional methods of data fitting and illustrate the advantages of computer simulation and introduce the methods of analysis.
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Affiliation(s)
- Kenneth A Johnson
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, TX, United States.
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2
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Dangerfield TL, Johnson KA. Design and interpretation of experiments to establish enzyme pathway and define the role of conformational changes in enzyme specificity. Methods Enzymol 2023; 685:461-492. [PMID: 37245912 DOI: 10.1016/bs.mie.2023.03.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We describe the experimental methods and analysis to define the role of enzyme conformational changes in specificity based on published studies using DNA polymerases as an ideal model system. Rather than give details of how to perform transient-state and single-turnover kinetic experiments, we focus on the rationale of the experimental design and interpretation. We show how initial experiments to measure kcat and kcat/Km can accurately quantify specificity but do not define its underlying mechanistic basis. We describe methods to fluorescently label enzymes to monitor conformational changes and to correlate fluorescence signals with rapid-chemical-quench flow assays to define the steps in the pathway. Measurements of the rate of product release and of the kinetics of the reverse reaction complete the kinetic and thermodynamic description of the full reaction pathway. This analysis showed that the substrate-induced change in enzyme structure from an open to a closed state was much faster than rate-limiting chemical bond formation. However, because the reverse of the conformational change was much slower than chemistry, specificity is governed solely by the product of the binding constant for the initial weak substrate binding and the rate constant for the conformational change (kcat/Km=K1k2) so that the specificity constant does not include kcat. The enzyme conformational change leads to a closed complex in which the substrate is bound tightly and is committed to the forward reaction. In contrast, an incorrect substrate is bound weakly, and the rate of chemistry is slow, so the mismatch is released from the enzyme rapidly. Thus, the substrate-induced-fit is the major determinant of specificity. The methods outlined here should be applicable to other enzyme systems.
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Affiliation(s)
- Tyler L Dangerfield
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, United States
| | - Kenneth A Johnson
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, United States.
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3
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Johnson RS, Strausbauch M, McCloud C. An NTP-driven mechanism for the nucleotide addition cycle of Escherichia coli RNA polymerase during transcription. PLoS One 2022; 17:e0273746. [PMID: 36282801 PMCID: PMC9595533 DOI: 10.1371/journal.pone.0273746] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Accepted: 08/15/2022] [Indexed: 11/06/2022] Open
Abstract
The elementary steps of transcription as catalyzed by E. coli RNA polymerase during one and two rounds of the nucleotide addition cycle (NAC) were resolved in rapid kinetic studies. Modelling of stopped-flow kinetic data of pyrophosphate release in a coupled enzyme assay during one round of the NAC indicates that the rate of pyrophosphate release is significantly less than that for nucleotide incorporation. Upon modelling of the stopped-flow kinetic data for pyrophosphate release during two rounds of the NAC, it was observed that the presence of the next nucleotide for incorporation increases the rate of release of the first pyrophosphate equivalent; incorrect nucleotides for incorporation had no effect on the rate of pyrophosphate release. Although the next nucleotide for incorporation increases the rate of pyrophosphate release, it is still significantly less than the rate of incorporation of the first nucleotide. The results from the stopped-flow kinetic studies were confirmed by using quench-flow followed by thin-layer chromatography (QF-TLC) with only the first nucleotide for incorporation labeled on the gamma phosphate with 32P to monitor pyrophosphate release. Collectively, the results are consistent with an NTP-driven model for the NAC in which the binding of the next cognate nucleotide for incorporation causes a synergistic conformational change in the enzyme that triggers the more rapid release of pyrophosphate, translocation of the enzyme along the DNA template strand and nucleotide incorporation.
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Affiliation(s)
- Ronald S. Johnson
- Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, North Carolina, United States of America
- * E-mail:
| | - Mark Strausbauch
- Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, North Carolina, United States of America
| | - Christopher McCloud
- Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, North Carolina, United States of America
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4
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Prasher P, Sharma M. Medicinal chemistry of pyrophosphate mimics: A mini review. Drug Dev Res 2021; 83:3-15. [PMID: 34506652 DOI: 10.1002/ddr.21877] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2021] [Revised: 08/20/2021] [Accepted: 08/24/2021] [Indexed: 12/21/2022]
Abstract
The pyrophosphate mimicking groups offer rational modification of the pyrophosphate-bearing natural substrates of the overexpressed enzymes that cause the onset of disease progression. Mainly, the modified substrate interacts differently with the enzyme active site eventually causing its deactivation, or provides the therapeutically active products at the completion of the catalytic cycle that contribute toward the inhibition of the target enzyme. Many of the pyrophosphate mimic-containing molecules serve as competitive or allosteric inhibitors of the target enzyme to achieve the desirable properties for the mitigation of the target enzyme's pathophysiology. This review presents an epigrammatic overview of the pyrophosphate mimics in medicinal chemistry.
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Affiliation(s)
- Parteek Prasher
- UGC Sponsored Centre for Advanced Studies, Department of Chemistry, Guru Nanak Dev University, Amritsar, India.,Department of Chemistry, University of Petroleum & Energy Studies, Dehradun, India
| | - Mousmee Sharma
- UGC Sponsored Centre for Advanced Studies, Department of Chemistry, Guru Nanak Dev University, Amritsar, India.,Department of Chemistry, Uttaranchal University, Dehradun, India
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5
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Fagan SP, Mukherjee P, Jaremko WJ, Nelson-Rigg R, Wilson RC, Dangerfield TL, Johnson KA, Lahiri I, Pata JD. Pyrophosphate release acts as a kinetic checkpoint during high-fidelity DNA replication by the Staphylococcus aureus replicative polymerase PolC. Nucleic Acids Res 2021; 49:8324-8338. [PMID: 34302475 PMCID: PMC8373059 DOI: 10.1093/nar/gkab613] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 06/29/2021] [Accepted: 07/21/2021] [Indexed: 12/22/2022] Open
Abstract
Bacterial replication is a fast and accurate process, with the bulk of genome duplication being catalyzed by the α subunit of DNA polymerase III within the bacterial replisome. Structural and biochemical studies have elucidated the overall properties of these polymerases, including how they interact with other components of the replisome, but have only begun to define the enzymatic mechanism of nucleotide incorporation. Using transient-state methods, we have determined the kinetic mechanism of accurate replication by PolC, the replicative polymerase from the Gram-positive pathogen Staphylococcus aureus. Remarkably, PolC can recognize the presence of the next correct nucleotide prior to completing the addition of the current nucleotide. By modulating the rate of pyrophosphate byproduct release, PolC can tune the speed of DNA synthesis in response to the concentration of the next incoming nucleotide. The kinetic mechanism described here would allow PolC to perform high fidelity replication in response to diverse cellular environments.
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Affiliation(s)
- Sean P Fagan
- Wadsworth Center, New York State Department of Health, Albany, NY, USA.,Department of Biomedical Sciences, University at Albany, Albany, NY, USA
| | - Purba Mukherjee
- Wadsworth Center, New York State Department of Health, Albany, NY, USA.,Department of Biomedical Sciences, University at Albany, Albany, NY, USA
| | - William J Jaremko
- Wadsworth Center, New York State Department of Health, Albany, NY, USA
| | - Rachel Nelson-Rigg
- Wadsworth Center, New York State Department of Health, Albany, NY, USA.,Department of Biomedical Sciences, University at Albany, Albany, NY, USA
| | - Ryan C Wilson
- Wadsworth Center, New York State Department of Health, Albany, NY, USA
| | - Tyler L Dangerfield
- Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, TX, USA
| | - Kenneth A Johnson
- Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, TX, USA
| | - Indrajit Lahiri
- Wadsworth Center, New York State Department of Health, Albany, NY, USA.,Department of Biomedical Sciences, University at Albany, Albany, NY, USA.,Department of Biological Sciences, Indian Institute of Science Education and Research, Mohali, Punjab, India
| | - Janice D Pata
- Wadsworth Center, New York State Department of Health, Albany, NY, USA.,Department of Biomedical Sciences, University at Albany, Albany, NY, USA
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6
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Measurement of Nucleotide Hydrolysis Using Fluorescent Biosensors for Phosphate. Methods Mol Biol 2021; 2263:289-318. [PMID: 33877604 DOI: 10.1007/978-1-0716-1197-5_13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Assays for the detection of inorganic phosphate (Pi) are widely used to measure the activity of nucleotide hydrolyzing enzymes, such as ATPases and GTPases. The fluorescent biosensors for Pi, described here, are based on fluorescently labeled versions of E. coli phosphate-binding protein (PBP), which translates Pi binding into a large change in fluorescence intensity. In comparison with other Pi-detection systems, these biosensors are characterized by a high sensitivity (sub-micromolar Pi concentrations) and high time resolution (tens of milliseconds), and they are therefore particularly well suited for measurements of phosphate ester hydrolysis in real time. In this chapter, it is described how the Pi biosensors can be used to measure kinetics of ATPase and GTPase reactions, both under steady state and pre-steady state conditions. An example protocol is given for determining steady state kinetic parameters, Km and kcat, of the ATP-dependent chromatin remodeler Chd1, in a plate reader format. In addition, the measurement of Pi release kinetics under pre-steady state conditions is described, including a detailed experimental procedure for a single turnover measurement of ATP hydrolysis by the ABC-type ATPase SufBC using rapid mixing.
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7
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Abstract
The protein HIV Reverse Transcriptase (HIV RT) synthesizes a DNA strand according to a template. During the synthesis, the polymerase slides on the double stranded DNA to allow the entry of a new nucleotide to the active site. We use Molecular Dynamics simulations to estimate the free energy profile and the time scale of the DNA-protein's relative displacement in the complex's closed state. We illustrate that the presence of the catalytic magnesium slows down the process. Upon removing the catalytic magnesium ion, the process is rapid and significantly faster than reopening the active site in preparation for the new substrate. We speculate that magnesium regulates DNA translocation. The magnesium locks the DNA into a specific orientation during the chemical addition of the nucleotide. The release of Mg2+ eases DNA sliding and the acceptance of a new substrate.
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Affiliation(s)
- Hao Wang
- Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Ron Elber
- Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, Texas 78712, United States.,Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
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8
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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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9
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Dangerfield TL, Johnson KA. Conformational dynamics during high-fidelity DNA replication and translocation defined using a DNA polymerase with a fluorescent artificial amino acid. J Biol Chem 2020; 296:100143. [PMID: 33273013 PMCID: PMC7857513 DOI: 10.1074/jbc.ra120.016617] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Revised: 12/02/2020] [Accepted: 12/03/2020] [Indexed: 12/21/2022] Open
Abstract
We address the role of enzyme conformational dynamics in specificity for a high-fidelity DNA polymerase responsible for genome replication. We present the complete characterization of the conformational dynamics during the correct nucleotide incorporation forward and reverse reactions using stopped-flow and rapid-quench methods with a T7 DNA polymerase variant containing a fluorescent unnatural amino acid, (7-hydroxy-4-coumarin-yl) ethylglycine, which provides a signal for enzyme conformational changes. We show that the forward conformational change (>6000 s−1) is much faster than chemistry (300 s−1) while the enzyme opening to allow release of bound nucleotide (1.7 s−1) is much slower than chemistry. These parameters show that the conformational change selects a correct nucleotide for incorporation through an induced-fit mechanism. We also measured conformational changes occurring after chemistry and during pyrophosphorolysis, providing new insights into processive polymerization. Pyrophosphorolysis occurs via a conformational selection mechanism as the pyrophosphate binds to a rare pretranslocation state of the enzyme–DNA complex. Global data fitting was achieved by including experiments in the forward and reverse directions to correlate conformational changes with chemical reaction steps. This analysis provided well-constrained values for nine rate constants to establish a complete free-energy profile including the rates of DNA translocation during processive synthesis. Translocation does not follow Brownian ratchet or power stroke models invoking nucleotide binding as the driving force. Rather, translocation is rapid and thermodynamically favorable after enzyme opening and pyrophosphate release, and it appears to limit the rate of processive synthesis at 4 °C.
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Affiliation(s)
- Tyler L Dangerfield
- Institute for Cellular and Molecular Biology, Department of Molecular Biosciences, University of Texas, Austin, Texas, USA
| | - Kenneth A Johnson
- Institute for Cellular and Molecular Biology, Department of Molecular Biosciences, University of Texas, Austin, Texas, USA.
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10
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Villalba B, Johnson KA. Rate-limiting pyrophosphate release by hepatitis C virus polymerase NS5B improves fidelity. J Biol Chem 2020; 295:16436-16444. [PMID: 32938715 DOI: 10.1074/jbc.ra120.015394] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2020] [Revised: 09/04/2020] [Indexed: 01/02/2023] Open
Abstract
The hepatitis C virus RNA-dependent RNA polymerase NS5B is responsible for the replication of the viral genome. Previous studies have uncovered NTP-mediated excision mechanisms that may be responsible for aiding in maintaining fidelity (the frequency of incorrect incorporation events relative to correct), but little is known about the fidelity of NS5B. In this study, we used transient-state kinetics to examine the mechanistic basis for polymerase fidelity. We observe a wide range of efficiency for incorporation of various mismatched base pairs and have uncovered a mechanism in which the rate constant for pyrophosphate release is slowed for certain misincorporation events. This results in an increase in fidelity against these specific misincorporations. Furthermore, we discover that some mismatches are highly unfavorable and cannot be observed under the conditions used here. The calculated fidelity of NS5B ranges between 10-4-10-9 for different mismatches.
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Affiliation(s)
- Brian Villalba
- Institutes for Cell and Molecular Biology, University of Texas at Austin, Austin, Texas, USA
| | - Kenneth A Johnson
- Institutes for Cell and Molecular Biology, University of Texas at Austin, Austin, Texas, USA.
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11
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Wang H, Huang N, Dangerfield T, Johnson KA, Gao J, Elber R. Exploring the Reaction Mechanism of HIV Reverse Transcriptase with a Nucleotide Substrate. J Phys Chem B 2020; 124:4270-4283. [PMID: 32364738 DOI: 10.1021/acs.jpcb.0c02632] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Enzymatic reactions consist of several steps: (i) a weak binding event of the substrate to the enzyme, (ii) an induced fit or a protein conformational transition upon ligand binding, (iii) the chemical reaction, and (iv) the release of the product. Here we focus on step iii of the reaction of a DNA polymerase, HIV RT, with a nucleotide. We determine the rate and the free energy profile for the addition of a nucleotide to a DNA strand using a combination of a QM/MM model, the string method, and exact Milestoning. The barrier height and the time scale of the reaction are consistent with experiment. We show that the observables (free energies and mean first passage time) converge rapidly, as a function of the Milestoning iteration number. We also consider the substitution of an oxygen of the incoming nucleotide by a nonbridging sulfur atom and its impact on the enzymatic reaction. This substitution has been suggested in the past as a tool to examine the influence of the chemical step on the overall rate. Our joint computational and experimental study suggests that the impact of the substitution is small. Computationally, the differences between the two are within the estimated error bars. Experiments suggest a small difference. Finally, we examine step i, the weak binding of the nucleotide to the protein surface. We suggest that this step has only a small contribution to the selectivity of the enzyme. Comments are made on the impact of these steps on the overall mechanism.
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Affiliation(s)
- Hao Wang
- Oden Institute for Computational Engineering and Sciences, University of Texas, Austin Texas 78712, United States
| | - Nathan Huang
- Department of Molecular Biosciences, University of Texas, Austin, Texas 78712, United States
| | - Tyler Dangerfield
- Department of Molecular Biosciences, University of Texas, Austin, Texas 78712, United States
| | - Kenneth A Johnson
- Department of Molecular Biosciences, University of Texas, Austin, Texas 78712, United States
| | - Jiali Gao
- Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455-0431, United States
| | - Ron Elber
- Oden Institute for Computational Engineering and Sciences, University of Texas, Austin Texas 78712, United States.,Department of Chemistry, University of Texas, Austin, Texas 78712, United States
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12
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Larsen KP, Choi J, Prabhakar A, Puglisi EV, Puglisi JD. Relating Structure and Dynamics in RNA Biology. Cold Spring Harb Perspect Biol 2019; 11:11/7/a032474. [PMID: 31262948 DOI: 10.1101/cshperspect.a032474] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Recent advances in structural biology methods have enabled a surge in the number of RNA and RNA-protein assembly structures available at atomic or near-atomic resolution. These complexes are often trapped in discrete conformational states that exist along a mechanistic pathway. Single-molecule fluorescence methods provide temporal resolution to elucidate the dynamic mechanisms of processes involving complex RNA and RNA-protein assemblies, but interpretation of such data often requires previous structural knowledge. Here we highlight how single-molecule tools can directly complement structural approaches for two processes--translation and reverse transcription-to provide a dynamic view of molecular function.
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Affiliation(s)
- Kevin P Larsen
- Department of Structural Biology, Stanford University School of Medicine, Stanford, California 94305.,Biophysics Program, Stanford University, Stanford, California 94305
| | - Junhong Choi
- Department of Structural Biology, Stanford University School of Medicine, Stanford, California 94305.,Department of Applied Physics, Stanford University, Stanford, California 94305
| | - Arjun Prabhakar
- Department of Structural Biology, Stanford University School of Medicine, Stanford, California 94305.,Biophysics Program, Stanford University, Stanford, California 94305
| | - Elisabetta Viani Puglisi
- Department of Structural Biology, Stanford University School of Medicine, Stanford, California 94305
| | - Joseph D Puglisi
- Department of Structural Biology, Stanford University School of Medicine, Stanford, California 94305
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13
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Larsen KP, Mathiharan YK, Kappel K, Coey AT, Chen DH, Barrero D, Madigan L, Puglisi JD, Skiniotis G, Puglisi EV. Architecture of an HIV-1 reverse transcriptase initiation complex. Nature 2018; 557:118-122. [PMID: 29695867 PMCID: PMC5934294 DOI: 10.1038/s41586-018-0055-9] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2017] [Accepted: 03/19/2018] [Indexed: 11/29/2022]
Abstract
Reverse transcription of the HIV-1 RNA genome into double-stranded DNA is a central step in infection1 and a common target of antiretrovirals2. The reaction is catalyzed by viral reverse transcriptase (RT)3,4 that is packaged in an infectious virion along with 2 copies of dimeric viral genomic RNA5 and host tRNALys3, which acts as a primer for initiation of reverse transcription6,7. Upon viral entry, initiation is slow and non-processive compared to elongation8,9. Despite extensive efforts, the structural basis for RT function during initiation has remained a mystery. Here we apply cryo-electron microscopy (cryo-EM) to determine a three-dimensional structure of the HIV-1 RT initiation complex. RT is in an inactive polymerase conformation with open fingers and thumb and with the nucleic acid primer-template complex shifted away from the active site. The primer binding site (PBS) helix formed between tRNALys3 and HIV-1 RNA lies in the cleft of RT and is extended by additional pairing interactions. The 5′ end of the tRNA refolds and stacks on the PBS to create a long helical structure, while the remaining viral RNA forms two helical stems positioned above the RT active site, with a linker that connects these helices to the RNase H region of the PBS. Our results illustrate how RNA structure in the initiation complex alters RT conformation to decrease activity, highlighting a potential target for drug action.
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Affiliation(s)
- Kevin P Larsen
- Program in Biophysics, Stanford University, Stanford, CA, USA.,Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Yamuna Kalyani Mathiharan
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA
| | - Kalli Kappel
- Program in Biophysics, Stanford University, Stanford, CA, USA
| | - Aaron T Coey
- Program in Biophysics, Stanford University, Stanford, CA, USA.,Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Dong-Hua Chen
- Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Daniel Barrero
- Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Lauren Madigan
- Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Joseph D Puglisi
- Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Georgios Skiniotis
- Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA.,Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA
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14
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Malik O, Khamis H, Rudnizky S, Kaplan A. The mechano-chemistry of a monomeric reverse transcriptase. Nucleic Acids Res 2018; 45:12954-12962. [PMID: 29165701 PMCID: PMC5728418 DOI: 10.1093/nar/gkx1168] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Accepted: 11/08/2017] [Indexed: 01/28/2023] Open
Abstract
Retroviral reverse transcriptase catalyses the synthesis of an integration-competent dsDNA molecule, using as a substrate the viral RNA. Using optical tweezers, we follow the Murine Leukemia Virus reverse transcriptase as it performs strand-displacement polymerization on a template under mechanical force. Our results indicate that reverse transcriptase functions as a Brownian ratchet, with dNTP binding as the rectifying reaction of the ratchet. We also found that reverse transcriptase is a relatively passive enzyme, able to polymerize on structured templates by exploiting their thermal breathing. Finally, our results indicate that the enzyme enters the recently characterized backtracking state from the pre-translocation complex.
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Affiliation(s)
- Omri Malik
- Faculty of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel.,Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Hadeel Khamis
- Faculty of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel.,Faculty of Physics, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Sergei Rudnizky
- Faculty of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Ariel Kaplan
- Faculty of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel.,Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa 32000, Israel
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15
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Atis M, Johnson KA, Elber R. Pyrophosphate Release in the Protein HIV Reverse Transcriptase. J Phys Chem B 2017; 121:9557-9565. [PMID: 28926712 DOI: 10.1021/acs.jpcb.7b08320] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Enzymatic reactions usually occur in several steps: a step of substrate binding to the surface of the protein, a step of protein reorganization around the substrate and conduction of a chemical reaction, and a step of product release. The release of inorganic phosphate-PPi-from the matrix of the protein HIV reverse transcriptase is investigated computationally. Atomically detailed simulations with explicit solvent are analyzed to obtain the free energy profile, mean first passage time, and detailed molecular mechanisms of PPi escape. A challenge for the computations is of time scales. The experimental time scale of the process of interest is in milliseconds, and straightforward molecular dynamics simulations are in sub-microseconds. To overcome the time scale gap, we use the algorithm of Milestoning along a reaction coordinate to compute the overall free energy profile and rate. The methods of locally enhanced sampling and steered molecular dynamics determine plausible reaction coordinates. The observed molecular mechanism couples the transfer of the PPi to positively charged lysine side chains that are found on the exit pathway and to an exiting magnesium ion. In accord with experimental findings, the release rate is comparable to the chemical step, allowing for variations in substrate (DNA or RNA template) in which the release becomes rate determining.
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Affiliation(s)
- Murat Atis
- Institute for Computational Engineering and Sciences, The University of Texas at Austin , Austin, Texas 78712, United States
| | - Kenneth A Johnson
- Department of Molecular Biosciences, The University of Texas at Austin , Austin, Texas 78712, United States
| | - Ron Elber
- Institute for Computational Engineering and Sciences, The University of Texas at Austin , Austin, Texas 78712, United States.,Department of Chemistry, The University of Texas at Austin , Austin, Texas 78712, United States
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16
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Figiel M, Krepl M, Poznanski J, Golab A, Šponer J, Nowotny M. Coordination between the polymerase and RNase H activity of HIV-1 reverse transcriptase. Nucleic Acids Res 2017; 45:3341-3352. [PMID: 28108662 PMCID: PMC5389522 DOI: 10.1093/nar/gkx004] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Accepted: 01/03/2017] [Indexed: 11/17/2022] Open
Abstract
Replication of human immunodeficiency virus 1 (HIV-1) involves conversion of its single-stranded RNA genome to double-stranded DNA, which is integrated into the genome of the host. This conversion is catalyzed by reverse transcriptase (RT), which possesses DNA polymerase and RNase H domains. The available crystal structures suggest that at any given time the RNA/DNA substrate interacts with only one active site of the two domains of HIV-1 RT. Unknown is whether a simultaneous interaction of the substrate with polymerase and RNase H active sites is possible. Therefore, the mechanism of the coordination of the two activities is not fully understood. We performed molecular dynamics simulations to obtain a conformation of the complex in which the unwound RNA/DNA substrate simultaneously interacts with the polymerase and RNase H active sites. When the RNA/DNA hybrid was immobilized at the polymerase active site, RNase H cleavage occurred, experimentally verifying that the substrate can simultaneously interact with both active sites. These findings demonstrate the existence of a transient conformation of the HIV-1 RT substrate complex, which is important for modulating and coordinating the enzymatic activities of HIV-1 RT.
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Affiliation(s)
- Malgorzata Figiel
- Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, 02-109 Warsaw, Poland
| | - Miroslav Krepl
- Institute of Biophysics, Academy of Sciences of the Czech Republic, 612 65 Brno, Czech Republic.,Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University Olomouc, 77146 Olomouc, Czech Republic
| | - Jaroslaw Poznanski
- Institute of Biochemistry and Biophysics Polish Academy of Sciences, 02-106 Warsaw, Poland
| | - Agnieszka Golab
- Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, 02-109 Warsaw, Poland
| | - Jirí Šponer
- Institute of Biophysics, Academy of Sciences of the Czech Republic, 612 65 Brno, Czech Republic.,Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University Olomouc, 77146 Olomouc, Czech Republic
| | - Marcin Nowotny
- Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, 02-109 Warsaw, Poland
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17
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Shock DD, Freudenthal BD, Beard WA, Wilson SH. Modulating the DNA polymerase β reaction equilibrium to dissect the reverse reaction. Nat Chem Biol 2017; 13:1074-1080. [PMID: 28759020 PMCID: PMC5605435 DOI: 10.1038/nchembio.2450] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2016] [Accepted: 06/28/2017] [Indexed: 12/20/2022]
Abstract
DNA polymerases catalyze efficient and high fidelity DNA synthesis. While this reaction favors nucleotide incorporation, polymerases also catalyze a reverse reaction, pyrophosphorolysis, removing the DNA primer terminus and generating deoxynucleoside triphosphates. Since pyrophosphorolysis can influence polymerase fidelity and sensitivity to chain-terminating nucleosides, we analyzed pyrophosphorolysis with human DNA polymerase β and found the reaction to be inefficient. The lack of a thio-elemental effect indicated that it was limited by a non-chemical step. Utilizing a pyrophosphate analog, where the bridging oxygen is replaced with an imido-group (PNP), increased the rate of the reverse reaction and displayed a large thio-elemental effect indicating that chemistry was now rate determining. Time-lapse crystallography with PNP captured structures consistent with a chemical equilibrium that favored the reverse reaction. These results highlight the importance of the bridging atom between the β- and γ-phosphates of the incoming nucleotide in reaction chemistry, enzyme conformational changes, and overall reaction equilibrium.
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Affiliation(s)
- David D Shock
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, North Carolina, USA
| | - Bret D Freudenthal
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, North Carolina, USA.,Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, Kansas, USA
| | - William A Beard
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, North Carolina, USA
| | - Samuel H Wilson
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, North Carolina, USA
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18
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Structural Insights into HIV Reverse Transcriptase Mutations Q151M and Q151M Complex That Confer Multinucleoside Drug Resistance. Antimicrob Agents Chemother 2017; 61:AAC.00224-17. [PMID: 28396546 DOI: 10.1128/aac.00224-17] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2017] [Accepted: 03/28/2017] [Indexed: 12/26/2022] Open
Abstract
HIV-1 reverse transcriptase (RT) is targeted by multiple drugs. RT mutations that confer resistance to nucleoside RT inhibitors (NRTIs) emerge during clinical use. Q151M and four associated mutations, A62V, V75I, F77L, and F116Y, were detected in patients failing therapies with dideoxynucleosides (didanosine [ddI], zalcitabine [ddC]) and/or zidovudine (AZT). The cluster of the five mutations is referred to as the Q151M complex (Q151Mc), and an RT or virus containing Q151Mc exhibits resistance to multiple NRTIs. To understand the structural basis for Q151M and Q151Mc resistance, we systematically determined the crystal structures of the wild-type RT/double-stranded DNA (dsDNA)/dATP (complex I), wild-type RT/dsDNA/ddATP (complex II), Q151M RT/dsDNA/dATP (complex III), Q151Mc RT/dsDNA/dATP (complex IV), and Q151Mc RT/dsDNA/ddATP (complex V) ternary complexes. The structures revealed that the deoxyribose rings of dATP and ddATP have 3'-endo and 3'-exo conformations, respectively. The single mutation Q151M introduces conformational perturbation at the deoxynucleoside triphosphate (dNTP)-binding pocket, and the mutated pocket may exist in multiple conformations. The compensatory set of mutations in Q151Mc, particularly F116Y, restricts the side chain flexibility of M151 and helps restore the DNA polymerization efficiency of the enzyme. The altered dNTP-binding pocket in Q151Mc RT has the Q151-R72 hydrogen bond removed and has a switched conformation for the key conserved residue R72 compared to that in wild-type RT. On the basis of a modeled structure of hepatitis B virus (HBV) polymerase, the residues R72, Y116, M151, and M184 in Q151Mc HIV-1 RT are conserved in wild-type HBV polymerase as residues R41, Y89, M171, and M204, respectively; functionally, both Q151Mc HIV-1 and wild-type HBV are resistant to dideoxynucleoside analogs.
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19
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Li A, Ziehr JL, Johnson KA. A new general method for simultaneous fitting of temperature and concentration dependence of reaction rates yields kinetic and thermodynamic parameters for HIV reverse transcriptase specificity. J Biol Chem 2017; 292:6695-6702. [PMID: 28255091 DOI: 10.1074/jbc.m116.760827] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Revised: 02/21/2017] [Indexed: 11/06/2022] Open
Abstract
Recent studies have demonstrated the dominant role of induced fit in enzyme specificity of HIV reverse transcriptase and many other enzymes. However, relevant thermodynamic parameters are lacking, and equilibrium thermodynamic methods are of no avail because the key parameters can only be determined by kinetic measurement. By modifying KinTek Explorer software, we present a new general method for globally fitting data collected over a range of substrate concentrations and temperatures and apply it to HIV reverse transcriptase. Fluorescence stopped-flow methods were used to record the kinetics of enzyme conformational changes that monitor nucleotide binding and incorporation. The nucleotide concentration dependence was measured at temperatures ranging from 5 to 37 °C, and the raw data were fit globally to derive a single set of rate constants at 37 °C and a set of activation enthalpy terms to account for the kinetics at all other temperatures. This comprehensive analysis afforded thermodynamic parameters for nucleotide binding (Kd , ΔG, ΔH, and ΔS at 37 °C) and kinetic parameters for enzyme conformational changes and chemistry (rate constants and activation enthalpy). Comparisons between wild-type enzyme and a mutant resistant to nucleoside analogs used to treat HIV infections reveal that the ground state binding is weaker and the activation enthalpy for the conformational change step is significantly larger for the mutant. Further studies to explore the structural underpinnings of the observed thermodynamics and kinetics of the conformational change step may help to design better analogs to treat HIV infections and other diseases. Our new method is generally applicable to enzyme and chemical kinetics.
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Affiliation(s)
- An Li
- From the Institute for Cell and Molecular Biology, Molecular Biosciences Department, University of Texas at Austin, Austin, Texas 78712
| | - Jessica L Ziehr
- From the Institute for Cell and Molecular Biology, Molecular Biosciences Department, University of Texas at Austin, Austin, Texas 78712
| | - Kenneth A Johnson
- From the Institute for Cell and Molecular Biology, Molecular Biosciences Department, University of Texas at Austin, Austin, Texas 78712
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20
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Li A, Li J, Johnson KA. HIV-1 Reverse Transcriptase Polymerase and RNase H (Ribonuclease H) Active Sites Work Simultaneously and Independently. J Biol Chem 2016; 291:26566-26585. [PMID: 27777303 DOI: 10.1074/jbc.m116.753160] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2016] [Revised: 10/20/2016] [Indexed: 01/15/2023] Open
Abstract
HIV reverse transcriptase plays a central role in viral replication and requires coordination of both polymerase and RNase H activities. Although this coordination is crucial in viral replication, whether a DNA/RNA hybrid can simultaneously engage both active sites has yet to be determined as structural and kinetic analyses have provided contradictory results. Single nucleotide incorporation and RNase H cleavage were examined using presteady-state kinetics with global data analysis. The results revealed three interconverting reverse transcriptase-DNA/RNA species; 43% were active for both sites simultaneously, 27% showed only polymerase activity, and the remaining 30% were nonproductive. Our data clearly demonstrated that the DNA/RNA hybrid could contact both active sites simultaneously, although the single nucleotide incorporation (105 s-1) was ∼5-fold faster than the cleavage (23 s-1). By using a series of primers with different lengths, we found that a string of at least 4-6 nucleotides downstream of the cleaving site was required for efficient RNA cleavage. This was corroborated by our observations that during processive nucleotide incorporation, sequential rounds of RNA cleavage occurred each time after ∼6 nucleotides were incorporated. More importantly, during processive primer extension, pyrophosphate (PPi) release was rate-limiting so that the average rate of nucleotide incorporation (∼28 s-1) was comparable with that of net RNA cleavage (∼27 nucleotides(s)). Although polymerization is efficient and processive, RNase H is inefficient and periodic. This combination allows the two catalytic centers of HIVRT to work simultaneously at similar speeds without being tightly coupled.
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Affiliation(s)
- An Li
- From the The University of Texas at Austin, Institute for Cell and Molecular Biology, Department of Molecular Biosciences, Austin, Texas 78712
| | - Jiawen Li
- From the The University of Texas at Austin, Institute for Cell and Molecular Biology, Department of Molecular Biosciences, Austin, Texas 78712
| | - Kenneth A Johnson
- From the The University of Texas at Austin, Institute for Cell and Molecular Biology, Department of Molecular Biosciences, Austin, Texas 78712
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